HEADS UP!!!

Site upgrade in progress... Core site functions are working, but some non-critical features/functions will be temporarily unavailable while we work to restore them over the next couple of weeks.

Please post any bugs you encounter, but before you do, check to see if it's already listed.

Thanks for your patience while we work to improve the community.

• entries
46
• comments
332
• views
250,305

### About this blog

Moto Mind is a technical blog written by Paul Olesen who is a powertrain engineer working in the motorcycle industry. The blog covers a wide variety of topics relating to two and four stroke engine performance, design, and optimization.

## DIY Piston Ring Compressor

Today I want to share a quick tip with those of you who are working on your own engines but just can’t justify buying a set of piston ring compressors. It’s entirely possible to make a perfectly good ring compressor from materials you can get at the hardware store. All you need is some plumber’s pipe hanging tape and a hose clamp that is sized according to your cylinder bore.

To construct a DIY ring compressor from plumber's pipe hanger tape you will need to determine the length of tape required. This is easily done using the following equation for calculating the circumference of a circle.

Length of Tape Required = Piston Diameter x π (Pi)

When the tape is wrapped around the piston tightly, the final length may need to be reduced slightly so that the ends don’t butt together. Once the tape has been cut to length, make sure whichever side of the tape will be contacting the rings is smooth and free of little plastic burrs that could catch the rings.

Simply lube up the tape, tighten down the hose clamp, and you are in business.

Do you have a tip that makes compressing rings easier or cheaper? If so, leave a comment below!

- Paul

If you enjoyed this tip and want access to more like it, check out my book, The Four Stroke Dirt Bike Engine Building Handbook. On the fence about the book? Check out what other riders are saying: Thumper Talk Review

Available at:

## Help! - Bike Only Starts When Pushed

Today I want to talk about a situation I hear all too often. Someone’s bike, whether it be a two-stroke or four-stroke, only starts when it is pushed.

Before I discuss potential causes for this scenario, take a moment to think through the situation yourself.

What mechanical factors would result in either a two-stroke or four-stroke only starting when it is bump started?

In either case, the reason the engine is able to start when it is push started is because it is able to build more compression than it otherwise could when it is kicked or the electric starter is engaged. More compression is achievable because the cranking RPM is higher than what’s possible with the aforementioned starting methods. With a higher cranking RPM for a four-stroke, more air will fill the cylinder on the intake stroke, and for a two-stroke the scavenging process will be improved. With this being the case we must look at reasons why the engine is struggling to build compression in the first place.

Starting problems specific to four-strokes:
1. Valve seat recession - When a valve seat wears out and recedes, the valve moves up towards the camshaft. This leads to diminished valve clearances and if left to run its course, the valve and shim will bottom on the camshaft’s base circle. The next time the valve clearances are checked the problematic valve will be re-shimmed so the clearances are correct. Once this is done, the valve will have a gap between it and its corresponding seat.

2. The valve is bent - A valve with a serious bow to it may get jammed up inside the guide and not return all the way back to its seat. Bent valves typically result from an over-revved engine where the valves contact the piston. Valves can also bend to a lesser extent if they were mated to valve seats that were not cut concentrically to the guides, or they were paired with worn seats.

3. The valve stuck in the guide - This is usually due to the engine overheating. When the engine overheated the clearance between the valve and guide diminished which caused metal to transfer from one part to the other, ultimately ruining the surface finish on one or both parts. Once this happens the valve may be prone to sticking in the guide until the engine warms up.

4. The valves and seats do not seal well - Worn valves and valve seats can compromise the seal between them. Valve and seat wear is a natural part of running an engine but can also be accelerated by ingesting dirty air.

Starting problems specific to two-strokes:

1. The reed valve is worn - Reed petals that don’t close all the way, are chipped, or bent will not allow sealing of the crankcase and efficient gas flow up from the crankcase into the cylinder.

2. An engine seal or gasket has failed - A two-stroke engine requires a well sealed crankcase and cylinder in order for it to scavenge gases efficiently. A worn crank seal, leaky base gasket, or problematic power valve seal can all make starting more difficult.

Two and four-stroke problems:

1. The piston rings are worn - Worn piston rings will allow compressed gases to escape past them.

2. The head gasket or o-rings are leaking - Usually a leaking cylinder head will be accompanied by white smoke if coolant is being pushed into the combustion chamber, by coolant being blown out the radiator, or both.

I hope you found this rundown of potential problems useful for diagnosing bikes that like bump starting over a kick or the push of a button. Can you think of any other problems that would lead to lack of compression? If so, leave a comment and share them.

If you liked this post and want more technical info, check out my book, The Four Stroke Dirt Bike Engine Building Handbook. In it you will find over 300 pages of technical knowledge to help you get off on the right foot when rebuilding!

- Paul

## Help Moto Mind Help You + A Quick Tech Tip

I hope you all had a good holiday season and are excited for 2017. The ice bike has been kicking my butt so far, but I’m thankful I’ve been able to get out and ride. I’m definitely excited for the new year and today I wanted to discuss my upcoming blogs and share a quick tech tip with you.

My blog post pool is low right now and I’d like your help! Looking ahead to 2017 I want to deliver informative posts tailored to what you need to know and want learn. In the comments section below be sure to share your thoughts on what you’d like to learn about this year. Whether it’s maintenance, tuning, suspension, two-stroke, four-stroke, or anything else-- I want to hear what you have to say.

Depending on post length it takes me anywhere from 2 - 5 hours to write a piece I feel comfortable publishing for you, so I want to make sure I’m spending my time covering topics that are truly beneficial and relevant.

Moto Mind Quick Tech Tip
Anytime you drain fluids from something you’re working on and halt progress (think waiting for parts) tag the throttle or any other visible location and note that there’s no fluid in the machine.

This isn’t always applicable but here’s an instance of when it was. I’ve moved a few times in the last couple years and during that transitional period my bikes were five hours away in northwestern Wisconsin. One weekend I was set to make the trip back home to go riding, certain that my bike was ready to go. I got there and found that I’d left myself a tag noting that I was only part way through the oil change I so vividly remember completing. While I usually check my sight glass anyway, I can’t say I always do, especially if I’m in a hurry. Whether or not I would have caught the lack of oil without the tag I will never know, but I’m just glad I left myself a visual reminder.

If there’s something you’d like to learn about, please leave a comment below and I’ll see what I can do to work it into this year’s blogging schedule!

Plus, if you got socks or other stuff you didn't want over the holidays, be sure to check out my book and treat yourself!

- Paul

## Do You Know The Importance of Tightening Techniques?

I hope you’re all enjoying the fall weather. For those of you in northern states, I hope that you’re getting in some end of season riding. This month I want to touch on bolted joints and the importance of adhering to tightening techniques outlined in your model’s service manual.

How A Clamped Joint Works
I’m going to discuss the importance of criss-cross patterns, tightening sequences, incremental steps, and joint lubrication but first I want to explain how a bolted joint works. As a bolt is tightened to secure a pair of parts, the bolt will stretch a very small amount. The stretch in the bolt creates tension or preload in the joint which is the force that keeps the joint together. The amount of preload created is dependent on bolt size, bolt material, the torque applied, and the friction between the threads. There are additional variables, however a discussion on bolt engineering would be very long and not all that exciting! As long as you understand the basics for engine building you can begin to appreciate the importance of correctly tightening fasteners.

As you are well aware, an engine consists of many parts fastened together. What you may not consider as much is that the majority of these parts are fastened by more than one fastener. This means that how much you tighten/preload one fastener will have an effect on the surrounding fasteners. This interaction between the fasteners begins to shed light on why tightening sequences are so important.

The evenness of the preload across the bolts securing a part can affect part life. Warpage can occur in parts which are improperly tightened, ultimately rendering the part useless. A prime example of a part that can warp is a four-stroke cylinder head. If the bolts are unevenly tightened over time, the cylinder head can become permanently distorted. Gasket sealing problems can also occur from improper preloading of bolts across a part. In order for a gasket to seal it must be evenly compressed. If one area of a gasket is highly compressed and tensioned while another area is not, the gasket can easily leak through the low tensioned area. In the case of plain bearing bores, such as the cam cap, uneven preloading may cause the bearing bore to distort. As a result the cam may become difficult to turn. Or if run, the cam bearing bore will wear unevenly and in severe cases the cam could seize.

While ensuring bolt preload is even can be a problem there are three tightening techniques that virtually eliminate the issue. If you’ve been building engines for any length of time you’ve probably already been utilizing these techniques. Hopefully now you may have a better understanding of why the service manual instructs you to tighten parts a specific way.

Criss-Cross Patterns
Criss-cross patterns are called out when tightening or loosening parts with a simple square pattern or circular bolt pattern. These basic patterns have been around for a very long time and are a proven method for evenly distributing clamping load across a part. Most cylinder heads will utilize this type of clamping pattern.

Tightening Sequences
For more complex bolt patterns, such as those found on cam carriers and crankcases, the manufacturer will usually identify a specific sequence for tightening and loosening the fasteners. This sequence is based on testing and the past experiences of the manufacturer.

Incremental Steps
Highly torqued bolts, such as those found on the cylinder head, are almost always tightened and loosened in incremental steps. An incremental tightening sequence consists of torquing all the fasteners to a specific torque value, then increasing the torque and tightening again, and finally arriving at the final torque value. This sequence is typically performed in two to three steps.

Here’s something important to keep in mind regarding incremental steps! When torquing bolts in steps the change in torque between the steps must be large enough to induce bolt movement. For example if a bolt was torqued to 35Nm at the first step and the second step was 38Nm this would not be enough of a change to make the bolt move at the second step. The torque wrench would not overcome the friction of the stationary bolt and would hit 38Nm before the bolt even moves. As a rule of thumb incremental changes should be no less than 5Nm and if possible should be greater.

Lubrication
For highly torqued fasteners often times the service manual will specify that the threads of the fastener must be lubricated. The lubricant can be as simple as fresh engine oil or a specifically formulated thread lubricant product.

Adhering to any lubrication guidelines is of utmost importance. Since we most commonly measure torque to determine whether a bolt has been tightened/preloaded enough any change in the amount of force required to turn the bolt will influence the resulting bolt preload for a given torque value. The force required to turn a bolt is partially dependent on the amount of friction in the joint. If we had two identical fasteners where one was lubricated and the other was not, and we set the torque wrench to the same value for each, then both were tightened, the resulting bolt preload would be different between the two. Due to the reduced friction in the lubricated joint the bolt would stretch more and the preload in the joint would be higher at the specified torque wrench setting than the unlubricated joint. Depending on the criticality of the joint this can be a really big deal! It also shows why in some applications (think two piece conrods) directly measuring bolt stretch is a more accurate means of determining bolt preload.

I hope you enjoyed this quick summary of tightening techniques and their importance! If you have tips of your own you’d like to share or other pearls of wisdom please leave a comment.

For those of you interested in more engine building knowledge check out my book, The Four Stroke Dirt Bike Engine Building Handbook. You’ll find more detailed and comprehensive info on engine building there. Simply follow the links below. Thanks for reading and have a great week!

-Paul

## Do You Know How To Properly Inspect a Clutch?

Having a clutch that works correctly is key to being able transfer all the power your engine produces to the rear wheel (or wheels if you're a quad guy/gal). In this post I want to share some key clutch inspection techniques I use and recommend to help ensure your clutch works as it should. These tips are presented in a step by step format and are taken right from my book, The Four Stroke Dirt Bike Engine Building Handbook.

Basket Inspection
Inspect the driven gear which is secured to the basket. Look for damaged gear teeth and other imperfections. Grasp the gear and basket firmly, then try to twist the gear. The gear is secured to the basket either with rivets or fasteners. With use, the rivets or fasteners can loosen causing the gear to become loose. Most baskets use round rubber dampers to locate the gear to the basket, which are sandwiched behind the backing plate. The dampers can wear out and break, which will create excessive play between the gear and basket. Any looseness may have been accompanied by excessive gear noise or rattling sounds when the engine was previously running.

On baskets with loose gears and riveted backing plates the corrective action which will need to be taken is to either replace the basket or drill the rivets out. The idle gear may need to be pressed off in order to remove the backing plate. Once this is done, holes can be tapped and bolts installed which will secure the gear in place. Any rubber dampers that have worn can be replaced with aftermarket options. Check out this article for more details on clutch basket damper replacement: How to repair your clutch basket dampers for less than \$30.

Inspect the needle bearing bore surface on the basket next. Run your fingernail across the bore feeling for signs of wear. The bearing surface should be smooth and free of imperfections. If the surface is grooved or worn the basket will need to be replaced.

Inspect the area inside the basket where the large thrust washer resides. Wear should be minimal in this area. If any grooving is present, the needle bearing and spacer the basket rides on may have worn causing the basket to wobble or the pressed in steel insert has backed out, ultimately causing the face of the basket to rub on the edges of the washer.

Check for bent clutch basket fingers on the basket. Then look for grooving on the basket fingers where the clutch discs come in contact with the fingers. Grooving is caused by the clutch discs slamming into the clutch basket fingers. Normally grooving will be more pronounced on the drive side fingers. Grooving is not abnormal and occurs through usage of the clutch.

If any grooving is present, use the end of a pick to evaluate how deep the grooves are. Any grooving that can catch the end of the pick is also likely to be able to catch the edge of the clutch discs. When this happens, the clutch will have difficulty engaging and disengaging. If your bike had clutch disengagement/engagement problems prior to disassembly, basket grooving is the most probable cause.

A file can be used to smooth the grooves so the discs no longer catch, however deep grooving is an indication that the basket is near the end of its life. When filing clutch basket fingers, attempt to remove as little material as possible and remove material evenly from all the fingers.

Some manufacturers provide a specification for the clearance between the clutch disc tang and the basket fingers. This clearance can be measured by temporarily installing a clutch disc into the basket and using a set of lash gauges to check the clearance between the two parts. Both the clutch disc tangs and basket fingers will wear so if the clearance is outside the service limit it may be possible to prolong the life of the basket by installing new clutch discs. This is a short term fix however, and replacing both components at once is advisable.

Bearing/Spacer Inspection
Inspect the clutch hub needle bearing and spacer for signs of wear. The needle bearing will be replaced with a new bearing, but if the spacer is in good condition it will be reused. Check for grooving or concavity along the surface of the spacer where the bearing rotates. While the needle bearing won’t be reused, it can be inspected as well to help confirm any problems associated with the clutch basket or spacer.

Hub Inspection
There are two main areas on the clutch hub which will wear. First, grooving can occur on the splines which locate the clutch plates to the hub. The grooves are a result of normal clutch use and occur when the steel clutch plates rotate back and forth in the spline grooves. Any grooving which catches the end of a pick should be considered problematic. Careful filing to smooth the grooves or hub replacement are the two options available for remedying the issue. The clutch plates must be able to easily slide back and forth along the hub, otherwise clutch disengagement/engagement problems will occur.

The second area susceptible to wear on the clutch hub is at the back face of the hub. This is where the outer clutch disc contacts the hub. When the clutch is engaged, the clutch disc and hub will rotate in unison. However, when the clutch is partially engaged or disengaged, the clutch disc will rub against the face of the hub causing both the hub and disc to wear. Look for uneven wear patterns and indications of how deep the clutch disc has worn into the clutch hub.

If the face of the clutch hub has worn excessively or unevenly, the hub should be replaced.

Pressure Plate Inspection
The interaction between the pressure plate and clutch disc is identical to the situation previously described between the clutch disc and clutch hub. Wear will occur on the face of the pressure plate which contacts the outside clutch disc. Determine the condition of the pressure plate by looking for signs of excessive or uneven wear on the face of the pressure plate.

Disc and Plate Inspection
Both the clutch discs and clutch plates are designed to be wear items which will need replacement from time to time. Thickness and straightness are the primary inspection criteria used to determine if either component requires replacement. If there are any problems with any of the discs or plates replacing them as a set is best.

Clutch Disc and Clutch Plate Inspection
Clutch discs are made out of various compositions of fibrous materials which wear at different rates, while clutch plates are made from steel. Service manuals will specify a minimum thickness that the clutch discs and plates can be. This thickness can easily be measured by using a caliper. Take measurements at three to four locations around the clutch disc or plate to confirm either has not worn unevenly.

Once all the disc and plate thicknesses have been measured, both should be inspected for warpage. This can be done by laying the disc or plate on a surface plate or other flat surface. A set of lash gauges are used to determine any warpage. The service manual should specify a maximum warpage value which is usually around 0.006” (0.15mm). Attempt to insert the 0.006” lash gauge underneath the clutch disc or plate at multiple points. If the feeler gauge slides beneath either of the parts, those parts are warped and should be replaced.

Clutch discs which have been overheated due to excessive clutch fanning by the rider, not only may warp, but also emit an unpleasant stinky burnt smell. If a noticeable smell is present, the discs have overheated and should be replaced. Likewise, clutch plates that have overheated will likely be warped and exhibit discoloration. The discoloration is a sign of excessive heat build up. Once the clutch plates have overheated, the material properties of the plate change, the hardness is reduced, and the plate becomes less wear resistant. This means discolored plates should be replaced.

Lastly, inspect the clutch disc tangs for wear, chipping, or damage. If any tangs are damaged the disc should be replaced.

Clutch Spring Inspection
Over time and due to normal clutch use, the clutch springs will shorten. Clutch spring minimum free length specifications are provided by manufactures and can easily be measured using a caliper.

Clutch springs that are shorter than the minimum spec provided by the manufacturer will not have sufficient spring pressure to keep the clutch from slipping under heavy loads. Any springs at or past their service limits require the replacement of all springs as a set. This way when the new springs are installed, even pressure is applied to the pressure plate.

I hope you enjoyed this passage from my book detailing clutch inspection. If you have additional tips you'd like to share please leave a comment!

If you want more technical DIY dirt bike engine information, learn more about the book on our website or on Amazon. Simply follow the links below!

Thanks for reading!

-Paul

## Is A Piston Upgrade Right For You and Your Four-Stroke?

This month I wanted to share an exert from the Race and Performance Engine Building chapter in my book, The Four Stroke Dirt Bike Engine Building Handbook. If you've been wondering how high compression pistons work and if they are right for your application, read on!

Piston upgrades are normally considered when changing the compression ratio is desired or larger valves are installed. In both instances the shape of the piston is altered either to reduce the volume in the combustion chamber or to allocate additional room for larger valve pockets.

The compression ratio defines how much the original air/fuel mixture which was sucked into the engine is compressed. The following equation shows how an engine’s compression ratio can be calculated.

The swept volume is the volume that the piston displaces as it moves through its stroke. Mathematically this volume can be determined using the following equation.

The clearance volume is the volume of the combustion chamber when the piston is at top dead center (TDC). While manufacturers specify what the compression ratio should be, due to subtleties in manufacturing, parts vary slightly from engine to engine so finding the exact clearance volume of your engine actually requires measuring the clearance volume.

Undoubtedly you have probably heard that raising the compression ratio will increase the power of an engine. This is definitely true, however you should be aware of the other consequences that come along with this.

The more the air/fuel mixture can be compressed before it is combusted, the more energy which can be extracted from it. The reason for this is due to thermodynamic laws. In summary, the temperature difference between the combusted mixture when it is hottest and coolest determines the power and efficiency of the engine. The hottest point of the mixture will arrive shortly after the mixture has been ignited and the coolest point will occur around the point where the exhaust valves open. Since the temperature of a gas increases as its volume decreases, it is easy to see how increasing the compression ratio increases the overall combustion temperature. Something less obvious is that because the gases are compressed more, they will expand more and actually be cooler by the time the exhaust valves open.

If increasing the temperature of the compressed mixture is good, you might be wondering what keeps us from raising it higher and higher. Detonation, which is a by product of the additional heat and pressure in the combustion chamber, is the main reason the compression ratio can’t be increased beyond a certain point. Detonation occurs after the spark plug has ignited the air/fuel mixture. Normally once the spark has ignited the mixture, the flame will propagate outwards from the spark plug evenly in all directions. When detonation occurs some of the remaining air/fuel mixture situated towards the edges of the combustion chamber spontaneously combusts before the flame reaches it. When this happens a large spike in combustion pressure occurs. If severe enough detonation can cause engine damage in the form of pitting on the piston crown, broken ring lands, and scuffing of the piston from overheating.

To combat detonation there are a few different parameters which can be tweaked to help alleviate the problem. The air/fuel ratio can be altered along with the engine’s ignition timing to change the peak combustion temperatures, a fuel with a higher octane rating can be used which will be more resistant to detonation, and upgrades to the cooling system can be carried out to help keep the combustion chamber cooler.

Along with increasing the likelihood of detonation as a result of increasing the compression ratio, the engine will also produce more heat. The cooling system must absorb this additional heat and be able to adequately cool the engine, otherwise overheating and detonation may be problematic. Radiator size, thickness, and the speeds at which you ride at all play a big role in how efficiently the cooling system operates.

Now that you have an understanding of how high compression pistons affect performance, you can consider if this will be a good modification for you. Aftermarket pistons are usually offered in a few different compression ratio increases. You will want to look closely to see if any high octane fuels will be required to use in conjunction with the piston and if any cooling system improvements are necessary.

For racers looking to extract all the power from their bike, adding a high compression piston is one of the things that will be necessary. If you do a lot of tight woods riding, hare scramble racing, or enduros where low speeds are the norm, you may want to shy away from raising the compression ratio as the cooling system will have difficulty dealing with the increased heat at low speeds where airflow is limited.

I hope you enjoyed this excerpt on piston modifications and how they affect an engine. If you liked this write up and are interested in learning more about performance options and four stroke engine building, pick up a copy of my book. Right now the book is on sale at 20% off our list price when you order within the next two weeks.

You can grab your discounted copy off our site here: The Four Stroke Dirt Bike Engine Building Handbook Or on Amazon: Amazon Book Store

Thanks for reading and have a great week!

-Paul

## What you really need to know about air filter maintenance

Air Filter Maintenance - What You Need To Know
In my last post I shared an account of what happens when dirt gets past the air filter and into an engine. This was a telling tale, however I want to go further and discuss key components of what can be done in terms of maintenance to limit the chances of sucking in dirt. Whether you ride a two-stroke or four-stroke, it makes no difference, the importance of keeping dirt out cannot be overstated.

I want to start off by thanking those that left constructive comments in my previous post. Your insights into filter maintenance are much appreciated and help reinforce what I’m about to share.

How often should I change my air filter?
This depends entirely on the conditions you ride in. Dusty dry conditions will warrant more frequent filter changes than a damp riding environment where dust is non-existent. The amount of dirt accumulation that is acceptable is subjective, but I always err on the safe side. As an example, my filters are blue when freshly oiled and as soon as they start to become blotchy and start to turn color I change them.

Can I change my air filter too often?
Yes and no. I say yes only because every time the filter is removed there is a chance for dirt to enter the engine. A sensible changing regimen decreases the odds of dirt getting into the engine as the filter is removed/installed.

What to Use
I’ve personally been using FFT filter oil, however, there are many great options out there. No Toil’s water based oil system is something I’ve heard good things about and would like to try too. Asking other riders or doing a quick search will certainly turn up more great options as well.

Removing the filter
The main point I want to mention here is to be careful when removing the filter from the airbox so that dirt does not come off the filter or surrounding areas and find its way into the intake. On most bikes, fitting the filter between the subframe is a tight fit and dirt can occasionally come off as the filter is pulled up.

To help prevent this, clean the subframe or any areas the filter is likely to contact prior to removing it. Also watch for dirt accumulation at the top of the filter between the sealing flange and airbox.

Airbox Cleaning
Prior to any cleaning efforts be sure to use an air box cover or stick a clean rag in the intake tract which will help ensure any dirt that is dislodged won’t make its way into the engine.

Filter Cleaning
The correct way to clean a filter depends entirely on the type of oil used. Petroleum based oils will require a two step cleaning process. First a solvent must be used which removes the majority of the dirt. Second, the filter must be cleaned in soapy water and rinsed.

Water based oils only require a one step cleaning process using soapy water or a water based filter cleaner.

Selecting Solvents for Cleaning Away Petroleum Oils
Air filters consist of multiple foam elements which are bonded together chemically with adhesives. Depending on the adhesives used in the filter, certain solvents may or may not react. If a reaction occurs, the joint can break down and the filter can be ruined.

When selecting a solvent, it is always a safe bet to follow the recommendations provided by the filter manufacturers. However, as many will point out through their own experiences, there are several potential solvents that can work in place of the manufacturer’s.

A quick forum search will surely result in an overwhelming number of hits on filter cleaning and potential solvent solutions. I personally use parts washing fluid which I've downgraded from the washer to a bucket.

Cleaning Technique
The biggest tip I can share here is to make sure you only squeeze the filter when cleaning, don’t twist it. Squeezing lessens the likelihood of the glued joints getting damaged.

Filter Oiling
The goal is to get complete uniform saturation without over oiling. This can be done a number of ways and is largely dependent on the method of application (rubbing in by hand, dunking in oil, spray on, etc.).

My preferred method is to dispense oil from a bottle and work it in by hand. I believe this process keeps the amount of excess oil at bay, isn’t too messy, and it’s relatively easy to get good uniform saturation.

Many filters have two stages, a coarse foam filter element good for trapping large particles and a fine element suited for trapping smaller contaminants. Be sure to work oil into both elements.

Remember when working the oil in to be gentle with the filter. Rub and squeeze but don’t twist.

Once the filter is saturated with oil remove any excess by carefully squeezing the filter. Ideally, very little excess oil should get squeezed out, but remember, this is entirely dependent of how generous oil was applied. After excess oil has vacated the filter a nice even thin layer of oil should be visible.

Batch
Filter oiling is a dirty job. No matter how hard I try, oil always seems to end up where I don’t want it. To make things messy less frequently, batch the filter cleaning and oiling process. Buy a few filters, oil them, use them, clean them, and then repeat the process all over again so the task isn’t done as regularly.

Keep the pre-oiled filters in Ziploc bags so that they’re ready to go when you need them.

Greasing the Flange
Is it necessary? I believe the directive to grease the flange of the filter may have originated long ago when the sealing flanges of filters were not predominantly foam. Nowadays whether grease is necessary or not is mostly personal preference accompanied by whether or not the filter cage and airbox seal flat to one another, and how tacky the oil is that is being used. Personally, I still use a waterproof grease on my filter rims, however I’m aware it is probably not necessary in all circumstances.

Installation
Keeping dirt off the freshly oiled filter during installation is the main challenge. There are a few helpful tips I can share for doing this.

First, make sure the bolt is installed in the filter cage! It’s frustrating when you forget it.

Once you’re ready to install the filter I find that rotating the filter 90 degrees to its normal direction so that it can more easily be slipped past the subframe makes things much easier. Once down in the airbox the filter can be rotated into position.

The other option is to use a plastic bag as a shield effectively covering the filter while it is being lowered down. Once in position the bag can be removed.

Wrap Up
I hope you’ve enjoyed my post on air filter maintenance. If you have any questions or comments please share them below!

For those of you interested in all things engine related check out my book, The Four Stroke Dirt Bike Engine Building Handbook for more awesome information. In honor of Independence Day we’re having a two week sale where you can save 15% by entering offer code july4th at checkout if you order before July 17th.

Thanks for reading!

-Paul

## How Much Damage Can An Improperly Cared For Air Filter Cause?

I thought this week it would be a good idea to share with you an example of what can happen when dirt gets passed an engine's air filter. This will be a short post, but a picture is worth a thousand words. In my next post I’ll go into detail on how to properly care for your air filter to help ensure that this never happens to you.

The series of photos below shows a sad case where dirt has found its way into the engine and wreaked havoc. The photos are all from the KX250F I bought on the cheap with the sole intention of rebuilding the engine and documenting the process for my book, The Four Stroke Dirt Bike Engine Building Handbook. Honestly, I couldn’t have bought a better bike for the project, nearly everything on the bike was worn out or screwed up from the previous owner.

Here is how the air filter and airbox looked prior to disassembly.

Here is the back side of the air filter. The filter was completely dry. There was no grease on the sealing face of the filter or the airbox flange. In this particular case, dirt could have got into the engine through the filter or between the filter and sealing flange. The amount of dried mud in the airbox and on the bike also makes me suspicious that muddy water got into the engine instead of just dirt. I honestly can’t say for certain.

The airbox itself was also extremely dirty.

Once the engine was disassembled I carefully examined the piston assembly and cylinder bore. At first, I could not get any of the rings to move freely. Only after I had pounded a pick between the ring ends of the compression ring was I able to get the compression ring off. As I removed the compression ring, a load of sand came with it.

This photo of the compression ring doesn’t do the situation justice. Some of the dirt was actually removed from the ring as I handled it.

Here is a close up of the compression ring. Note all the grit!

The oil rings didn’t fair any better, were just as stuck, and had a lot of dirt on them.

Here you can see dirt inside the ring grooves and at the edges.

Here is dirt I rubbed off the oil rings.

Miraculously (and fortunately for me) whether the engine sucked in dirty air or water, it happened quickly and stuck the rings to the piston so they could no longer seal correctly, and the engine subsequently lost compression and power in a hurry. This speculation is based on the fact that the cylinder bore showed no signs of excessive wear or damage and it measured well within the service limits. This is an outcome I never though possible and is hard to believe.

I hope you enjoyed this brief write up on the damage that can result from ingesting dirt, whether from abnormal circumstances such as dropping a running engine into a mud hole or simply neglecting to take care of the air filter when running the engine in dusty conditions. In my next post I’ll show you how to care for and install your filters so these problems don’t happen to you! Questions or comments are always welcome and I enjoy hearing from you all!

If you like my blog, click the "Follow this blog" button in the upper right. You must be registered to do this.

## How Do You Keep Track of Where Bolts Go During a Rebuild?

Alright guys, this week I just want to share a short and simple tip with you on how to stay more organized during an engine build.

When it comes to major engine maintenance or repairs, usually the engine covers have to come off or the crankcases must be split. The covers and cases are almost always retained using different length bolts. The repercussions of installing the bolts in the wrong order upon reassembly can be very damaging. This is especially true if you install a bolt that is too short for its location and only a couple of threads engage, ultimately stripping the threads when you tighten the bolt.

So what’s an easy way to keep track of cover or case bolts that are arranged in a pattern of different lengths?

My favorite way to organize these bolts is to take a thin piece of cardboard (think cereal box thickness) and then slit the approximate bolt pattern into the cardboard so that the bolts cannot get mixed up. A picture is worth a thousand words so check out the one below. You need not be an artist to apply this tip, simply slit the pattern, add a couple reference points and you’re done!

Do you have any organizational tips you’d like to share? Leave a comment below because I'd love to hear about them!

If you are looking for more helpful tips and engine building info, feel free to check out my book, The Four Stroke Dirt Bike Engine Building Handbook. You’ll find 301 pages filled with crucial and down-to-earth four-stroke engine building knowledge. You've got one more week left to use the offer code tt2016 and receive 15% off your order!

Paul

## What Changes In Valve Shim Size Can Tell You About Your Engine

I hope you enjoyed my last post on ice tire studding! The season in my neck of the woods has been a bit short this year and I may be getting back to the dirt sooner rather than later. Nonetheless, Part II, which covers mounting ice tires is now up on my blog. You can view it here: Ice tire mounting.

In today's post I'm going to shift focus back to the engine and talk a little about valve technology. Valve technology and manufacturing techniques have changed substantially from the earlier days of engine development and I want to share with you some information about the current valve technology being implemented in your engines. I also want to discuss one way you can get a feel for how much life is left in your valves. Let’s get started.

The following excerpt is copied directly from my book, The Four Stroke Dirt Bike Engine Building Handbook. If you want to learn more helpful tips, which will bring your maintenance knowledge and engine building skills to the next level, I’d like to invite you to pick up a copy of my book by clicking here. Be sure to use the offer code tt2016 to get 15% off when ordering!

Alright, on to valves shim sizes.

The cylinder head assembly of most engines will wear out before it resorts to telling you it has had enough by catastrophically failing. Diagnosing these wear signs and knowing when it is time to replace components is the key to keeping the cylinder head assembly from failing. Due to the aggressive camshaft profiles, high compression ratios, and high RPMs required to make a lot of power, the valves and seats typically are the first parts to wear out within the cylinder head. Worn valves and seats will cause the engine to become difficult to start, have low compression, and have reduced power.

Modern valves found in dirt bike engines are made from either titanium or stainless steel alloys. Regardless of valve material, modern valve faces are either coated in a variety of anti-wear materials or hardened using various hardening processes. Common examples of trade names you might be familiar with include diamond like coatings (DLC) and black diamond coatings. These coatings are typically harder than the base material of the valve and help the valve resist wear, which occurs from ingesting dirty air and repeatedly contacting the valve seat. Coating and hardening processes are only present at the surface of the valve face. Depending on the type of valve and process used to harden it, the coating thickness can range from as little as 0.0001” (0.003mm) to around 0.003” (0.076mm). An easy way to visualize the thickness of the coating is to pluck a hair from your head and either measure it or feel it between your fingers. Most human hairs are around 0.002” (0.05mm) which should give you a good idea of how thick the coatings used on the valves are.

The important takeaway here is that if the coating is only a few thousandths of an inch thick, the valve can only be adjusted a few thousandths of an inch before it will have worn through the coating. Monitoring the starting valve shim size once the engine has been broken in (or new valves installed) and comparing that size to the shims required the next time the clearances are adjusted is a great way to assess valve health. Normally within the first 3-5 hours of breaking in a new engine the valve shim sizes may change slightly. This is due to the mating of the new valves to the seats and any valve seat creep which may occur. After this occurs and the valves have been shimmed to compensate, usually an adjustment up to around 0.004” (0.10mm) is all that can be done before a valve has worn through its hardened surface. Once this happens the valve face will wear much more quickly and start to wear out the seat as well. This will result in more frequent valve shim intervals and necessitate the need for having the valve seats cut. By paying attention to changes in shim sizes you will be able to approximate when the valves have worn through their hardened surfaces and must be replaced.

Thanks for reading and please leave questions or comments below. I enjoy hearing from you!

Remember you can get 300 pages worth of in-depth dirt bike engine information with The Four Stroke Dirt Bike Engine Building Handbook. Be sure to use discount code tt2016 at checkout to receive 15% off your order!

-Paul

## Motorcycle Ice Tire Studding - Part One

Happy belated New Year's! I hope the holidays were good to you and that you're looking forward to a new season of two wheeled excitement. I know I am and I'm excited to get back to work on this blog.

In today’s post I’m going to get into the details related to tire studding with the help of an industry expert. To help bring you the best information I can on studding ice tires, I’ve enlisted Jarrett King of Two Wheel Endeavors to help with this article. For those of you that don’t know, Two Wheel Endeavours is heavily involved in supporting Canadian ice racing efforts and offers studded tires, ice racing accessories, and custom ice solutions. Jarrett was involved in the development of the Mitas Ice King tires, knows his craft, and brings a lot of knowledge to the table.

Many people are under the impression that there isn’t much to studding a pair of tires, just screw some screws in and you’re done right? There is actually a hefty amount of skill involved with studding tires. These skills come down to knowledge of screw angle, head position, and screw length. Of course there are many parameters which all affect how well the tire will perform, but today we are going to talk mostly about studding. This attention to detail is a huge reason that guys who have perfected the art of tire studding can make a living at it. I’m not saying this to scare you off from trying to stud your own tires, just that if you’re going to go for it, it will take some practice and advice from an expert.

Now I’m going to turn it over to Jarrett who will go into detail on the aspects of tire studding.

Key Factors Affecting Tire Performance by Jarrett King

Tire Choice: Selecting the right tires to stud is critical in terms of traction and tire life. Lug height, tread pattern, carcass thickness, and rubber composition all have a huge influence on how well a tire will work. Unfortunately, there is not a lot of data supplied by tire manufacturers available to help guide a person in the right direction, but there is plenty of empirical data floating around among the ranks of ice riding enthusiasts. To help get you started I put together a list of the most common ice tire choices.

Front Tires
Mitas Ice King - (Top Left)
Bridgestone ED11 - (Bottom Right)

Rear Tires
Mitas Ice King - (Top Right)
Kenda K335 - (Bottom Left)
Motoz X-Circuit - (Not Shown)

Tire Liners: Depending on the tire chosen, a liner can be used that will provide protection for the tube and allows for the use of longer screws. The liner is usually a cut up street tire which fits inside the chosen tire.

Pattern: The pattern in which the screws are laid out on the tire has a huge influence on the traction and grip characteristics of the tire. Specific patterns may be tailored to provide more grip or slip depending on the rider and how the tire is used.

Consistency: Care must be taken to ensure the screw pattern is consistent from one lug to the next. Any deviation in screw location and angle can cause the tire to wander as it moves over the ice.

Rim Trueness: The trueness of the rim can have a big effect on how the tire performs. A wonky rim can cause inconsistency in screw alignment. This can lead to similar handling problems because the screw pattern is not aligned accurately.

Screw Type: AMA or Canadian style screws are the primary options for competitive ice racing. The two screw types are defined below:

AMA screws - 3/16” head height, sizes #8 or #10, and range in length from ⅜” to 1 ½”

Canadian screws - ¼” head height, size #12, and range in length from 1” to 1 ½”

Along with the screw requirements for the different racing classes, keep in mind purpose made ice screws go through a different hardening process than normal hardware store screws, allowing them to stay sharp longer. If you’re going to stud a pair of tires and want longevity, be sure to use a good quality screw such as those offered by Kold Kutter.

Screw Threads: Fine thread screws are preferred because they do less damage to the rubber during installation. They are also easier to set to the correct height when fine tuning the screws.

Screw Angle: The angle the screw is driven into the tire dictates how the screw contacts the ice. The screw angle can be broken down into two parts, the fore/aft angle, and the side angle.

• Sweep: Tire builders refer to the fore/aft angle of the screw as the sweep angle. Ideally only the leading edge of the screw should make contact with the ice. This can be achieved by angling the screw anywhere from 10 to 30 degrees upon installation.

• Side Angle: Screws used to grip the ice when the bike is leaned over will be installed at an angle which complements the contour of the tire.

Head Alignment: The alignment of the slot in the screw head can be tuned to provide better grip in a given direction. For screws used for braking (front) and drive (rear) the screw slot is aligned perpendicular to the direction of travel. For cornering grip the slots of screws on the side of the tire are aligned parallel to the direction of travel.

Paul: Now that Jarrett has provided a great framework of what goes into studding a tire, we’re going to get into the specifics. It was mentioned previously that ice screws have three primary functions: braking, accelerating, and cornering. Next, we’ll get into the details of what makes each of these three types of screws functional for their specific purpose.

Braking Screws: Braking screws are at the rear of the lug on top, but when they are on the ground they are on the leading edge (biting edge) when under braking, thus the name “braking screw”. Sweep is used to prevent the screws from chattering on the ice under braking because of the fact that the crown would strike the ice at two points if installed flat. The magic sweep angle is the shallowest possible angle without the “rear” part of the screw crown biting in. With Canadian screws, this angle is much more straight up and down but still usually has 10 degrees or so. If you leaned them too far forward it will damage the knobs because the screw isn’t sunk into the liner enough, if you went straight in they will function but it makes the tire feel a bit strange under heavy braking.

Acceleration Screws: Again, there are differences between AMA and Canadian screws. The Canadian screws can go virtually straight in, AMAs need that biting edge so they don’t deflect or lose traction because of two different contact points. Picture a skate blade. The more sharp and precise the edge, the more ground pressure is focused on that area. Same with screw tips, if two parts of it hit the ice it will start to “float”. Optimal angle is shallowest possible (as close to straight up and down as possible) before the back edge of the screw starts touching the ice surface.

Side Grip Screws: Cornering screws are typically run in at one angle, there is no sweep to them. Some builders have tried adding some sweep, however, never with too much angle. If you run an ice tire over a piece of cardboard under lean you will see that the top edge of the screw is contacting the ice at an angle that prevents the front tire from low-siding. In essence these screws do the exact reverse thing that the rear tire does under acceleration.

Paul: The last thing Jarrett is going to talk about is the screw pattern and some of the compromises that are made while studding.

Jarrett: When it comes to general screw pattern and arrangement, there are a couple things to consider. First, is that on the rear tire the inverse “V” pattern is there for a reason… what it does is each screw passes the load onto the next screw while under lean (picture them passing sandbags to each other). To prove this, reverse a V-pattern tire, it will be all kinds of squirrely under acceleration and then the rear will try to jump out from under the bike when you hit the brakes, it’s truly scary.

My second point, ideal screw pattern is a balance between a few different factors. Knob spacing, contact pressure and knob count/pattern. On a tire like a Kenda, so many screws are striking the ice at once that the tire is floating on the surface of the ice. Traction is being gained by getting the maximum number of screw heads to hit the ice at the same time. This is great until the moment that there is a hint of snow on the lake and the tire begins to act like a crazy carpet under the bike. It floats because it can’t maintain ground pressure.

The old Pirelli Lagunacross tire became amazing the moment that Marcel Fournier came out with the modern Canadian Ice screw. The knob pattern was ideal (V shaped paddle) for the application and the knob spacing was super wide, which meant great ground pressure on each screw. Unfortunately that also meant a much larger radial load on the screws and knobs which often lead to premature knob or screw failure. The Mitas Ice King does not generate the same ground pressure as the Pirelli because the knobs are quite a bit closer but the tire’s compound and knob pattern allow for a much better balance of ground pressure (traction) to durability ratio. Using AMA screws, a Mitas Ice King does not benefit from additional screw rows the way that a Kenda will because it will float much quicker, but without as many screws contacting the ice.

Ice tire building is a compromise. The perfect ice tire doesn’t exist in the same way that there is no perfect Intermediate MX tire… but there are some that are MUCH more effective than others.

My third and final point, ice tires have been built in north America since the early 30s. The angle of screws is something that has been tried in multiple arrangements hundreds of times over. For someone getting into the sport their enthusiasm may make them believe that changing things will create a magic setup, but the reality is that a true set of wheels (no dings dents, warps), with consistent screw angles and heights, proper air pressures, and properly balanced is the most effective way to kick ass out on the ice racing track. Oh and don’t forget to duct-tape that face (frostbite sucks!).

Paul: Whether you're new to the sport or have a few seasons under your belt I hope you found Jarrett’s info on ice tires beneficial . Check the DIY Moto Fix website for part two in a week and here again for part three. For those of you in warm states I encourage you to take a trip to a cold destination and give ice riding a try! Be sure to check out Two Wheel Endeavors if you're in need of tires or anything else ice racing related. If you have any comments or want to share some info please leave a comment below.

-Paul
DIYMotoFix.com

## The Top 6 Characteristics You Need To Have To Rebuild An Engine

I hope you’re all having a good fall and are getting excited for the holidays. It snowed for the first time this year here in Wisconsin and I’m getting eager for the lakes to freeze over so I can get out and ride the ice. I need to set aside a good 7 hours to stud my tires and set up my bike before that can happen though!

Today I want to talk about six characteristics that are necessary to have when one sets out to build an engine. I’ve detailed how to tackle many different jobs, but honestly that is only half the battle. If you’re in a rush or lack the desire to understand the reasons behind what you’re doing, you will make mistakes and miss out on important things. Listed below are the traits that I believe can help you take your build to the next level.

1. Being Detail Oriented
What’s worse than getting started on a build only to realize you didn’t buy an important replacement part? Focussing on the details of a project can feel tedious at times but can pay off in the grand scheme of things. Before I get started on a project I spend a hefty amount of time researching what parts I’m going to replace and where the best prices are. Also, I will have a solid idea of the sequences I’ll use for disassembly and assembly. Another good habit for the detail oriented is to take notes throughout the build, which you can use at a later date should the need arise. When you have an appreciation for all the small details that go into a build, it will make for a much smoother project.

2. Having Patience
Have you ever been in a rush to do something and after you’re done you realize if you had spent just a bit more time the project could have turned out much better? I was this way with so many of the things I did when I was younger, but have learned to slow down and be patient as I work. Engines don’t go together instantaneously and being patient throughout the process, especially when things aren’t going as planned, is very important. There is nothing worse than making a huge mistake because you’re in a rush. Imagine finishing a build and realizing you left an important part on the table, depending on where the part came from, you just bought yourself another few hours of work. Trying to skimp on time more often than not costs you more time in the long run. Have patience and enjoy the process.

3. Being Observant
Just about every mechanical thing is gleaming with a story, and that story only reveals itself if you know what to look for. An engine is no different. From the parting lines on a component left by the casting tooling used to create it to wear patterns on a piston, there are hundreds of observations that can be made while working on an engine. As you work, keep an eye out for subtle anomalies that may tell you why something failed or broke. For example, things like snail tracks across a gasket, raised edges on gasket surfaces, or covers that don’t sit flat on a table - these are all good indicators of why a particular part was leaking.

4. Being Curious
Perhaps more appropriately titled, “a desire to understand mechanical workings”. It is incredible how much can be learned about the engine just by studying how specific parts interact within it. An engine is composed of many different subsystems and they must all work in order for the engine to function. By looking at the various interactions of the parts within an engine, the condition of the parts and reasons for any failures can be more easily understood. The next time you build an engine, challenge yourself to learn how all the different subsystems of the engine work. Once you learn this, diagnosing problems and identifying all the faulty parts becomes much easier.

5. Being Meticulous
The necessity to be thorough and meticulous throughout a build cannot be overstated. Whether it be taking extra steps to inspect components, measuring new parts, or taking extra time to ensure the condition of surrounding subsystems are okay, having meticulous tendencies can pay off. As an example, on more than one occasion I’ve purchased new parts that have been mispackaged or out of spec. Had I not made the choice to carefully measure the problematic new parts, I could have ended up with an engine that was destined to fail. While it may take more time to be meticulous throughout a build, there is a lot at stake, both in terms of time and money, making it all the more important to ensure everything is done correctly.

6. Having Ambition
Building an engine can be hard, things can go south unexpectedly, and projects can easily stall. Being ambitious and having a can-do attitude is important to ensure the engine doesn’t sit half torn apart in the garage never to be completed. Until you tear into the engine, you never know what you might find. I’ve disassembled engines many times in the past only to find I need to replace a lot more parts than I had planned (this seems to be my luck when I shop for bikes on Craigslist as of late). This can be a huge downer, but keeping the end goal of getting back out and riding in mind and having the desire to push through any and all obstacles is a must.

Do you have any engine building characteristics you want to share? Leave a comment below and tell everyone what you think it takes to build a great engine!

For those of you that believe you possess the characteristics of a good engine builder, be sure to check out my book, The Four Stroke Dirt Bike Engine Building Handbook, to learn more about the how and why behind engine building. Whether you want to be taught about the relationships between all the various parts within an engine, you are in need of pointers on picking the right performance parts, or you would like to see examples of wear patterns found on engine components, my book is here to guide and help you throughout your build.

With the holidays coming up, I want to extend a special four day offer to you for the handbook and all the other products at DIY Moto Fix. Between November 27th and November 30th if you purchase anything from DIY Moto Fix you will save 30% on your order. If you’ve got a significant other trying to do some holiday shopping for you, be sure to send the site their way before Monday the 30th

Save 30% and check out the book and other products by clicking this link: DIY Moto Fix

## How Does Octane Rating Affect Your Fuel?

Octane Ratings
In my last post I shared a tip I like to use when filling up fuel cans at the gas station. I also presented an example detailing how mixing two different fuels with different octane ratings affects the blended fuel's octane rating. Out of that post some comments were left regarding the necessity of running specific octane fuels. Today, I want to discuss the octane attribute of fuels in more detail.

What is the Octane Rating and How Is It Determined?
The octane rating associated with a fuel is a measurement of the fuel's resistance to detonation. To measure a fuel's octane rating it is either tested in accordance with test procedures established for the Motor Octane Number (MON) or the Research Octane Number (RON). In summary, a single cylinder engine with a variable compression ratio is used for testing. MON test procedures require the engine be run at 900RPM, inlet air temp be 38C, and ignition timing is set between 14 and 26 degrees BTDC (specific timing depending on the compression ratio). RON procedures are slightly less stringent with the engine operating at 600RPM, inlet temp between 20 and 52C (barometric pressure dependent), and the ignition timing fixed at 13 degrees BTDC.

The test fuel is run in the engine, the compression ratio is increased, and the point where the engine starts to detonate is observed. Once the test fuel has been run, its octane rating is determined by blending two base fuels together. Iso-octane with a RON of 100 and heptane with a RON of 0 are mixed together until the the engine detonates under the same conditions as the test fuel. By blending, the octane rating of the test fuel can be established. For example, if the blend of iso-octane and heptane resulted in a mixture of 13% heptane and 87% iso-octane then the test fuel would have an octane rating of 87.

What Rating System is Shown on Gas Pumps?
This depends where you live. In the United States the octane number on gas pumps is the average of the MON and RON numbers established for the fuel. In Europe the RON number is used. This is why if you ever go to a gas station in Europe it looks like they have higher grade octane fuels than we do in the U.S.

How Does the Octane Rating Affect Power?
The higher the octane rating of a fuel, the more resistance it has to detonation and pre-ignition. The more resistance a fuel has to detonation, the higher the engine's compression ratio can be set (within limits) or boost pressure if we're talking turbos.

When an engine is designed one of the driving parameters for development of the design is the type of fuel(s) that will be compatible with the engine. For example, if an engine is designed to work with fuels that have a minimum octane rating of 87, then the compression ratio of the engine must be limited to a value which ensures the engine never detonates when 87 octane fuel is used. For this example, say the compression ratio is 12:1. With a 12:1 compression ratio when fully optimized, the engine will produce a finite amount of power. Say 50hp.

Now take the same engine, raise the compression ratio to 13:1, and require a fuel with a 93 minimum octane rating be used in the engine. Due to the increase in compression ratio, the engine's power will increase. Perhaps to 52hp. This power increase is only possible by raising the compression ratio and increasing the octane rating (detonation resistance) of the fuel being used.

The takeaway here is that you will not see a power increase in an engine designed to run on 87 octane by putting in fuels with higher octane ratings without changing another parameter, such as the compression ratio. You would however increase the engine's detonation resistance by using a higher octane fuel. This may be beneficial if the engine is being operated under heavy loads or in harsh conditions where heat loads on the engine are abnormally high and the engine is more prone to detonation.

Wrap Up
I hope my brief explanation on octane ratings has shed some light on how they affect engine performance. As always, if you have questions or want to leave a comment please do so below. I enjoy hearing from you.

At this point, I want to thank everyone who has purchased a copy of my book. I appreciate the support and warm response to the release of the printed version. For those of you interested in the handbook please check it out by following this link: The 4t Handbook

## Filling Up At The Pump

How Residual Pump Fuel Affects Your Fill Up
This week I have a quick tip I want to share with you regarding buying fuel and filling up gas cans for your bikes. I know many of you, myself included, rely on premium grade gasoline dispensed from local gas station pumps to put endless grins on your faces. One of the downfalls of gas station pumps is that fuel from the previous sale is left in the hose. According to the American Petroleum Institute, the amount of fuel left in a gas pump's hose is around 1/3 of a gallon.

Generally speaking, when two fuels are blended the octane rating of the resulting fuel is approximately the average of the two fuels. So if you had a gallon of 87 octane and a gallon of 93 the resulting blend would have an octane rating of 90. I'll be the first to admit that 1/3 of a gallon of fuel added to a two gallon gas can won't have much effect on the octane rating. For those of you that like numbers, 0.33 of a gallon of 87 added to 1.67 gallons of 93 will yield the following octane rating:

0.33 gallon of 87 / 2 gallons = 16.5% of the total mixture
1.67 gallons of 93 /2 gallons = 83.5% of the total mixture

(0.165 x 87) + (0.835 x 93) = 92 octane blended fuel

So in a two gallon can, the octane rating of the fuel has dropped a point due to the 1/3 gallon of 87 in the pump hose. Unless you have a very well developed performance engine, this isn't anything to lose sleep over. I think a bigger reasons to want to keep that 1/3 of a gallon out of your can is due to the possibility of ethanol being in the hose from the previous sale. Many articles can be found outlining why ethanol should be avoided, but the main reasons include part corrosion due to the exposure to alcohol, rubber seals and o-rings may not be compatible with ethanol resulting in swelling and failure, and some plastics deteriorate when exposed to ethanol. Not to mention ethanol contains less energy than gasoline. Again, we're not talking about a large percentage of ethanol in the overall scheme of things but I prefer to stay away from the stuff when I can.

Fueling Tip
I'm very careful about what I run through my powersport engines. To safeguard against filling up a fuel can with residual fuel from the previous sale, I like to donate the first gallon of "premium" to my vehicle before filling my gas cans. This ensures whatever fuel was in the hose and pump is flushed out and that I'm filling up my cans with premium. If you are borderline OCD about what goes in your engines like I am, you may consider adopting this practice.

I suspect many of you have other tips and tricks regarding fueling. Leave a comment below and share your thoughts and experiences so other motorheads can benefit!

Book News
I also wanted to invite you to check out my book on how to build four-stroke engines, which is now officially available in print form. It took a ton of work to bring the print book together and get the right help on board. The project hasn't been easy, but I'm proud to offer this book to you and can assure you it will make a great addition to your workshop. You can learn more about the book by following this link: The Four Stroke Handbook

To celebrate the arrival of the print book, I'm running a sale until the 27th of September offering all versions of the book at a 20% discount. After the 27th the sale will end and the price will go up. If you've got a build coming up now or in the future and are interested in the book, now is a great time to pick up a copy.

Thanks for reading and have a great week!
-Paul

## Getting Started Servicing Shocks

Hey everyone, this week we're going to switch it up and talk shock absorbers! Over the last few months I've gotten many requests to broaden the topic spectrum and cover other dirt bike topics. So today, we'll do just that by discussing and providing some resources to get you familiar with servicing shocks.

I suspect many of you currently take your shock to someone to have it serviced when it needs to be freshened up. I also bet that it is usually a pain to be without a bike for perhaps a week and that it probably costs around \$100 each time? I know I always dreaded having suspension work done on my bike because it seemed to take forever, plus I always had to drive over an hour and half to the nearest shop. For me, those days are long gone. Now do all my suspension work myself.

I believe the majority of you are completely capable of servicing your shocks yourself, but just don't quite have all the pieces of the puzzle you need. Maybe you're not quite sure what tools you need; or once you get the shock apart, you don't know what parts you will have to replace? To help clarify what's needed to service a shock and answer some of the common questions about shock building, I created a detailed guide for you. The guide will help you decide if outsourcing your shock maintenance is the way to go or if you are in fact ready to take the job on yourself.

Before I discuss the details of the guide, I want to provide you with a little background on shock absorbers. For major motorcycle brands, shocks are sourced from the following companies: Showa, KYB , and Works Performance (WP). These three brands are primarily the companies responsible for equipping OEM bikes. Companies, such as Ohlins , cater more towards the aftermarket. Out of the three common OEM shock brand options, Showa and KYB are the go-to's for the Japanese manufacturers, while European brands, such as KTM, gravitate toward the WP brand. So if there is any question as to what brand of shock you have, you can keep this in mind. Out of the three common OEM brands, Showa and KYB shocks are very similar, while WPs feature a slightly different design.

The guide I created is geared towards those of you with either Showa or KYB shocks. Those of you with WP shocks may still find the guide useful, but there are a couple tools missing. Within the eight page guide, you'll be provided information on all the tools you need to service a Showa or KYB shock. These tools include any specialty tools and discuss shock pressurization options. Plus there are some pointers on how to make your own specialty tools if you are on a budget.

Once you get through the tools section you'll be presented with a detailed outline on replacement parts. Knowing what to replace within the shock when it is due for servicing is extremely important and the replacement parts section will walk you right through what you may need. It will also provide you with different options for buying replacement parts.

To receive the eight page guide and learn more about shock servicing, click the following link: Shock Building Tools and Replacement Parts Guide

Thanks for reading and feel free to comment below with any questions or concerns. Bringing high quality DIY advice is what Moto Mind is all about, and I enjoy hearing from all of you and your DIY experiences.

-Paul Olesen
DIY Moto Fix

## Leak Down Testing // Pt 2

Hey everybody, hope you are having a great summer thus far! I've been able to get on the bike a lot this summer and I hope you've been getting your fair share of riding in too. A couple weeks ago I covered what a leak down test is, in this blog post here, and how it can be used to determine engine problems. Today I’ll go through and detail how to do a leak down test on your dirt bike engine step-by-step. Now that we're past the halfway point of the summer riding season it may not be a bad idea to check in and see how your engine is doing by performing a leak down test.

How to Perform a Leak Down Test

To perform a leak down test you will need an air source capable of at least 115psi output pressure. Most leak down tests are performed at a regulated pressure of 100psi. This makes testing simple and the correlation of leakage a breeze since you’re working on a scale from 0-100. Lower test pressures such as 90psi can be used in the event that the air system isn’t capable of anything over 100psi or the specific leak down tester you have doesn’t work on a 100psi scale. Just remember if you test at a value other than 100psi, you will need to mathematically determine the leakage percentage since it is no longer a direct correlation.

Leakage testing can be tricky when working by yourself, so if you’re able to round up a friend to help you out it makes things a lot easier. With 100psi of pressure being applied to the piston it is a full time job making sure the piston and crankshaft don’t move. Even with a long breaker bar, holding the crank in place can be quite a task, couple that with having to operate the pressure regulator and obtain a good reading. Again, I highly recommend having two sets of hands on deck for this procedure.

How To Calibrate Your Leak Down Tester

A leak down tester consists of an air inlet, a pressure regulator, two pressure gauges, and an air outlet which pressurizes the cylinder. It is important to check to see if both pressure gauges read the same prior to any testing. If they do this is great, however occasionally the gauges won’t read exactly the same so a baseline will need to be established.

1. Start by setting your air source so that its output pressure is 115 psi. By setting the air source higher than the test pressure this will ensure it does not interfere with the pressure regulation during the test.

2. Slowly increase the leak down tester pressure by adjusting the regulator. Set the incoming air pressure to 100psi.

3. Once the incoming air pressure is set at 100psi read the outlet pressure gauge. If the outlet gauge reads 100psi you are good to go. If the outlet gauge is adjustable set the gauge so it also reads 100psi. If the outlet gauge is non-adjustable (most common) write down the outlet gauge pressure reading. Here you can see the outlet gauge reads 97psi. Since no pressure is being lost between gauges the only explanation for the difference in reading is gauge deviation. The 97psi value will be equivalent to 100psi.

4. After you have recorded the outlet gauge pressure that corresponds to the inlet gauge pressure you are ready to start leakage testing. Set the initial regulated pressure back to 0psi so that the tester doesn’t rapidly and unexpectedly pressurize the cylinder when you reconnect the air line for the test.

Leak Down Test Steps
1. Make sure the petcock is turned off and remove the fuel line from the carburetor or throttle body. Use a rag to catch any fuel draining from the line.

2. Remove the seat and fuel tank from the bike.

3 . Remove the radiator cap and pull out the crankcase breather tube.

4. Remove the spark plug cap . Prior to removing the plug blow compressed air into the plug cavity to rid it of dust and debris so that it can’t get into the engine. Then remove the spark plug.

5. Remove the crankshaft hole cap cover so that you can gain access to the crankshaft.

6. If working from the clutch side of the engine, rotate the engine over so that the piston is just shy of TDC (approximately the width of a punch mark off) on the compression stroke. There are usually alignment marks which can be used depending on the manufacturer to help gauge how close to TDC you are. On the Honda pictured there are punch marks on the crank and balances shaft gears denoting TDC. As you rotate through to just shy of TDC feel for compression building up in the cylinder. As you turn your wrench, resistance should build up as you approach TDC. If you do not feel resistance, rotate the engine over once more and realign to just shy of the TDC markings. This will take you from the exhaust stroke to the compression stroke where you should feel the compression start to build.

If working from the flywheel side of the engine, rotate the engine over so that the piston passes TDC by around a ¼ of a rotation of the crankshaft. Reverse direction and set the crank so that it is just past TDC using the applicable alignment marks. On the Kawasaki pictured you can see the alignment slots. As you came up on the compression stroke you should have felt a little bit of compression build up. If you do not feel resistance, rotate the engine over once more and realign to just shy of the TDC markings. This will take you from the exhaust stroke to the compression stroke where you should feel the compression start to build.

7. Install the leak down tester in the spark plug hole with the regulated pressure set at 0psi initially.

8. It usually takes a breaker bar and two hands to lock the crankshaft from moving once the cylinder is pressurized. This is where having an extra set of hands helps immensely. One person should focus on keeping the crankshaft in position while the other operates the leak down tester. Remember to set the piston just shy of TDC (whichever side is applicable for your application) and to lock the crankshaft in place while the piston is still traveling upwards so the rings sit in the bottom of the ring grooves.

9. Once the crankshaft is locked in place pressurize the cylinder. Slowly turn the pressure regulator up to 100psi.

10. Note the reading of the outlet pressure gauge. This corresponds to the amount of air the combustion chamber is retaining. If both pressure gauges read 100psi when they were calibrated the difference in pressure on the outlet gauge is the cylinder leakage. For example if the outlet gauge reads 95psi the cylinder leakage would be 5%.

If however during calibration both gauges did not read 100psi then the leakage will need to be calculated. For example if the outlet pressure gauge read 97psi during calibration and 92psi when the combustion chamber was pressurized, then the leakage could be found by dividing 92 by 97.

92 ÷ 97 = 0.948

0.948 x 100 = 94.8%
100 - 94.8 = 5.2% leakage

11. Open the throttle and listen for an audible hissing sound coming from the intake, exhaust, or crankcase breather. Also look in the radiator for air bubbles.

Here are the four problems that can result:

1. Air passing through the intake indicates leaking intake valves.
2. Air passing through the exhaust indicates leaking exhaust valves.
3. Air passing through the crankcase breather indicates worn rings.
4. Air bubbles forming in the radiator indicates a leaking head gasket.

12. Depressurize the combustion chamber by turning the regulator back so it is at 0psi and no air is entering the combustion chamber. Unhook the air source and disconnect the leak down tester.

13. Reinstall the spark plug and plug cap.

14. Reinstall the radiator cap and crankshaft hole cap.

15. Reinstall the fuel tank and seat.

That's all there is too it! I hope you have enjoyed my posts detailing how to perform a leak down test. With a little practice you will quickly be able to determine what is going on inside your engine and be better suited to detect major problems before they turn into engine failures. If you have questions, a technique you want to share, or want to leave a comment please do so below.

If you found this post helpful and want more information on how to diagnose engine problems or how to perform high quality engine builds in your own garage, check out my book, The Four Stroke Dirt Bike Engine Building Handbook. You can pick up the eBook immediately and the print book will be out soon!

Thanks for reading everyone!

Paul
DIY Moto Fix - Empowering and educating riders

## Save The Salt

I want to switch gears with this post and bring your attention to an issue that is near and dear to myself and many land speed racers. Over the past decade salt mining has caused track conditions at the Bonneville Salt Flats to become worse and worse. Years ago, the salt layer was up to 5 feet thick, today it is less than an inch in some places. Salt mining is partly to blame for the depletion of salt at Bonneville and holding racing events there is becoming extremely hard!

I know not many of you here on TT may participate at, or have ties to Bonneville, but this is great opportunity to band together as powersport enthusiasts and help out those that do. Please help your fellow motorheads by signing the following petition which asks for salt mining to stop at Bonneville. I've signed and hope you do too!

The salt flats at Bonneville are a special place and it would be unfortunate to not preserve them for future generations. Thanks everyone!

Paul

## Leak Down Testing // Pt I

Determining how healthy an engine is can be tricky business. I’ve previously covered compression testing (here and here), but now I want to discuss what a leak down test is and how to perform one on a four-stroke dirt bike engine. This will be a two part series, with the first part emphasising the details of a leakdown test, and the second part explaining in detail how to correctly perform a leak down test. Let’s get started! Leak down testing is a more definitive way to assess the health of an engine compared to compression testing because a leak down test allows the mechanic to pinpoint the problematic area within the engine. Whether the valves are no longer sealing, the rings are worn, or the head gasket is leaking - a leak down test can be used to find and diagnose all these potential issues.

The way a leak down test works is fairly simple. With the piston just shy of TDC and the valves closed (compression stroke), air pressurizes the cylinder to a defined pressure which is recorded by a pressure gauge. A second pressure gauge is used to monitor the amount of air escaping the combustion chamber. A comparison is made between the air going into the cylinder and the air escaping. The percentage of air escaping is used to determine the overall health of the engine.

The amount of air escaping can roughly be quantified to assess the condition of the engine. When race engines are built, the accuracy and precision that goes into the build results in the lowest leakage values. Most race engines will have a pressure loss of between 0% and 5%. Standard builds resulting in good running engines typically lose up to 15%. Any engine that is close to or past being ready for service will leak from 16% to 30%. These engines will most likely be running poorly, if at all. Engines beyond 30% leakage more often than not are broken and will not run. The more the engine leaks, the worse the engine’s health. Keep in mind these values are provided as a reference point and each engine can be a little different.

It is possible to pinpoint where leaks are coming from once the cylinder is pressurized. When performing the test, the throttle should be fully opened and the radiator cap should be removed. Air can exit the combustion chamber at four points: past the intake valves, past the exhaust valves, past the rings, or past the head gasket. Each of these four points will exhibit a unique tell-tale sign if air is leaking.

Intake valve leaks can be diagnosed by listening for air escaping out the carburetor or throttle body. Exhaust valve leaks can be found by listening for air escaping out the exhaust system. A leaking head gasket will result in air bubbles showing up at the radiator fill cap neck. Excessive leakage past the piston rings will result in pressurizing the crankcase and the resulting air can be traced out the crankcase or cylinder head breather hose. Air escaping past the rings may also be heard or felt passing through the access hole in the engine side cover, where the wrench has been inserted to position the crankshaft. The location at which the air exits when it leaks past the piston rings will depend if the engine has a separate crankcase cavity or a joint cavity. Usually on engines with a separate cavity, the air will be routed through a one way valve, which then directs the air up into the cylinder head and out the cylinder head breather hose.

I want to address one concern you may have at this point. You have probably heard before that the piston should be at TDC when performing a leak down test. In reality there are a couple issues with this that I am going to cover. First, with the short stroke engines of today, keeping the piston precisely at TDC with 100 psi of pressure pushing down on it is next to impossible. The piston and crank will want to rock to either side of TDC. Controlling which side of TDC the piston rests is important. Depending on which side of the engine is used to lock the crankshaft in place and the direction of rotation of the engine, the nut or bolt used to lock the crank in place may either try to tighten or loosen itself from the air pressure pushing against the piston. Even though these are highly torqued fasteners, the air pressure can still occasionally loosen the nut or bolt. This creates a serious problem, because now you’ve got to figure out how to lock out the crankshaft and retorque the nut or bolt.

The second issue is not so much a problem as it is a minor detail. To best simulate ring sealing conditions the rings should sit in the bottom of the ring grooves. This is how they would sit on a running engine and how the test should be performed. By ensuring the rings always sit in the bottom of their grooves, another level of repeatability is added to the test. Simply make sure when setting piston position that the piston is always traveling up just before you hold it in position. If you are working from the left side on a forward rotating engine, it will be necessary to rotate the piston past TDC then reverse direction so the rings sit in the bottom of their grooves and the flywheel nut will not try to loosen itself from the air pressure.

I hope you enjoyed my write up detailing leak down testing. Stay tuned for my next post where I’ll show you exactly how to perform a leak down test yourself. In my eBook, The Four Stroke Dirt Bike Engine Building Handbook, I cover leak down testing in further detail and invite you to pick up a copy if you want to learn more about how to diagnose engine troubles and build four-stroke engines.

If you have questions or thoughts, as always, I enjoy hearing them! Leave your comments below. Don't forget to follow my blog by clicking the button in the upper right hand corner of this page! Thanks everyone.

-Paul Olesen
DIY Moto Fix - Empowering And Educating Riders From Garage To Trail

## Cam Chain Wear and Replacement Tips

I hope you all are getting out on your bikes a lot this summer and are putting some time on them! This week’s post is dedicated to an engine part that is often overlooked, its importance not totally understood, and its service specs minimal. I’m talking about the timing chain. I want to discuss and share with you some signs that the cam chain is worn out.

Just like the drive chain, timing chains elongate, fatigue, and wear out. Luckily, they are not subject to dirt and mud, are bathed in an oil bath, and their overall environment is much better. Before I get into it, one misconception I want to clear up right away is that the timing chain doesn’t technically stretch. Instead, the pins and rotating elements of the chain wear. When the pins wear they become smaller and their mating holes grow larger leading to increased clearances and chain length.

When an engine is run with a worn timing chain engine performance is compromised and the likelihood of related failures is greatly increased (think chain tensioner). Cam timings that are off several degrees will result in a loss of power and the cam chain tensioner will have quite a job trying to take slack out of the valvetrain. When a timing chain elongates it may not do so in a uniform way and parts of the chain may be tighter or looser than others. While automatic cam chain tensioners have proven to be reliable on the majority of engines, some model years, brands, and individuals have fared better than others. A worn timing chain which adds extra slop and inconsistent chain tension to the valvetrain certainly won’t make the tensioner’s job any easier. So it makes a lot of sense to keep tabs on the condition of the chain itself from time to time.

When I was working on a Kawasaki KX250F engine build I took the time to do some comparisons which illustrate the differences you will see between a new and worn out cam chain. First, with the worn chain installed I checked the cam timing. Then I installed the new chain and rechecked the timing. In the table below you can see the intake cam timing was retarded by 6.625° and the exhaust by 9.50° when compared to the new cam chain timing values. For the average weekend warrior this may not seem like much but in terms of performance engines this is miles off the mark!

Next I looked at chain elongation. With both the new and old chain lying on the workbench it is easy to see a noticeable difference in chain length. The old chain is around 5mm longer than the new one.

You can also easily see how much more flexible the old chain is in comparison to the new chain as well.

These comparisons are all well and good but when do they become practical? Good question, since most of you won’t be checking the timing or removing the chain to compare it to a new one. Unfortunately, very few service manuals provide specifications or guidance on cam chains apart from the “inspect and replace as necessary” phrase commonly found throughout manuals. You may get lucky and find a pin to pin measurement spec you can use from time to time but it is not the norm. My suggestion is to document the applicable attributes of a new chain the next time you have one before installing it into your engine. This way you’ll have some tangible specs to compare to as the chain wears.

Method 1 - The Pin to Pin Measurement
One of my favorite methods to gauge chain wear is to compare pin to pin measurements of new and old chains. To do this you will need to know the total number of pins on the chain. It is easiest to count the number of pins prior to installing the chain, however, pins could still be counted with the chain installed in the engine by marking one of the links, rotating the engine around, and counting.

Once the total number of pins is known a measurement across a set number of pins is taken with the chain installed. I like to span around 6 - 8 pins between the sprockets on a twin cam engine. Unicam engines are trickier and the number of pins you can measure is usually less. It is important to try and measure across multiple pins because the variation between new and old chain measurements will be more pronounced this way. With the new chain installed I measure 1.846” (46.89mm) across eight pins. This is my benchmark measurement and is what I will compare all future measurements to.

Over time, the chain will wear and it will elongate. To keep tabs on chain wear it is never a bad idea to check the condition of the chain whenever you check valve clearances. In the image below I replaced the new chain with the old and repeated my pin to pin measurement across eight pins. This time I measure 1.860” (47.24mm).

The difference in length between the new and old chain can be seen in the table below.

A chain length increase across eight pins certainly isn’t earth shattering at first glance but that is only a fraction of the chain. To get a better idea of the total chain length increase and the severity of the problem some math is required. My cam chain totals 114 pins and since I only measured eight pins I will need to divide 8 into 114 to determine my length multiplier.

8 pin segments which fit into a 114 pin chain = 114/8 = 14.25

Once I have determined how many 8 pin segments fit into a 114 pin chain I can multiply this value by the change in length between the two chains to determine the total length the chain has increased.

Total Chain Length Increase (inches) = 0.014" x 14.25 =0.200"
Total Chain Length Increase (mm) = 0.36 x 14.25 =5.13mm

The calculated increase is accurate since this is about the difference in length I saw when I laid the chains side by side and measured them. If you aren’t familiar with what changes in length are acceptable this example can be considered one on the far end of the spectrum. The engine had been seriously neglected and wasn’t in real good shape.

Method 2 - What Does the Chain Tensioner Say?
The second way you can observe chain wear is by comparing cam chain tensioner plunger position throughout the chain’s life. To do this the tensioner is temporarily installed, set, and the engine turned over at least four times to allow the tensioner to self tension. Once the chain tensioner has absorbed the chain slack it is removed and the plunger position is noted. Remember to either install the chain tensioner stopper tool or remove the center bolt and spring, depending on tensioner design, so that the plunger doesn’t extend as the tensioner is removed.

In the image below I marked the plunger position with the new chain installed. As you can see the plunger is hardly extended and the second tooth on the plunger is engaged.

As the chain wears the plunger will have to extend out further and further to take up the slack. When I set the plunger with the old chain installed the ninth tooth was engaged on the plunger. Observations like this can be used to gauge cam chain wear and to determine when the chain should be replaced.

Method 3 - Alignment Marks and Feel

Every engine will have specific marks designed into components to aid in the timing of the engine. These marks can also be used to get an idea of the condition the timing chain is in. When correctly timed all alignment marks should be positioned nearly perfectly. As you can see in the image of the Kawasaki engine the two punch marks on the cam gears are aligned with the machined surface of the cylinder head. Both punch marks are visible and in the correct spot.

As the chain wears the tensioner will absorb slack and the cams will retard. In this image with the old chain installed the exhaust cam punch mark is far too high in relation to the cylinder head machined surface and the intake cam is not even visible. This is a good indication that the chain is worn and should be replaced.

Lastly, a basic feel of the tension of the chain between the cam gears can be performed if the engine is of twin cam design.
Here, with the old chain installed there is roughly 6-8mm of slack when I pull up on the chain.

Pushing down I get around the same 6-8mm of slack.

With the new chain installed I get around 3mm of slack when I pull up.

Finally, pushing down I also get around 3mm of slack.

I hope this write up gives you a few ideas of how you can gauge cam chain wear and that it makes you consider the condition your chain is currently in. I know these methods require a new chain to obtain quantifiable measurements, however, even if you don’t currently have anything to compare your chain to, this write up can be used to give you an idea of where your chain is at in its life. The examples I have provided are at the two extremes of the spectrum, being brand new and severely worn, and anything you encounter should fall between them. For those of you replacing your chain in the near future be sure to take a couple measurements so you have useful info to go off of down the road!

If you have additional tips and tricks relating to cam chain wear I’m all ears and am sure the TT community would love to hear them. For those of you who want to know even more about your engine and are performing your own maintenance check out my book on engine building by clicking here. The Four Stroke Dirt Bike Engine Building Handbook is full of practical engine building knowledge you can use on your next major or minor overhaul.

-Paul Olesen
DIY Moto Fix - Empowering And Educating Riders From Garage To Trail

## How To True A Dirt Bike Wheel Yourself

In my last blog post I covered how to lace up a wheel assembly with new spokes. This week I’ll discuss how to properly true the rim. Truing the rim is actually not too difficult. Once you understand the interaction between the spokes and rim, you will make quick work of the job.

To get started a truing stand of sorts needs to be set up. This doesn’t have to be anything special and I used a bench vice, adjuster block, rear axle, spacers, a series of old bearings and washers, and the axle nut. The reason I went to the trouble of clamping the hub in place was to eliminate any possibility of the hub sliding back and forth on the rim, which would make my truing efforts difficult.

This is by no means the only way to create temporary truing stand and you can use your imagination to come up with alternatives. Temporarily installing the wheel back into the swingarm may work equally well if you don’t have a bench vice.

Next, some sort of gauge will be needed so the amount of runout can be seen. I used a dial indicator attached to a magnetic base, however more simple solutions could easily be fabricated.

It isn’t absolutely necessary to measure runout, especially right away when major adjustments may need to be made. Instead you only need to see how the gap between the end of the pointer and rim changes as the wheel rotates. A coat hanger, piece of welding rod, or even a pencil could all be used to the same effect as the indicator shown.

Axial (side to side) runout will be corrected first. Here you can see there is a noticeable difference in gap size between the rim and pointer through a full revolution of the rim.

The goal is to tweak the tension in the spokes so that the gap between the rim and pointer is even as the rim is rotated.

To do this the gap can either be increased or decreased depending on which spokes are tightened or loosened. To decrease the gap, tighten the spokes originating on the side of the rim where you want the gap to decrease. In the previous photo I’m tightening the right side spokes, and in doing so I am pulling the rim to the right. An ⅛ to ¼ turn of the nipple is enough to induce a change. For the given area of the rim that must be pulled over, evenly tighten at least three of the surrounding spokes on the side being pulled. If the rim needs to shift a lot, loosen the opposite side spokes the same amount you have tightened the pull side spokes. This will help keep even tension on all spokes and help to shift the rim.

The process of tightening and loosening the spokes to pull the rim from side to side can be performed at all the high and low points surrounding the rim. Continue to turn and rotate the rim around until the gap between the rim and pointer evens out. Some areas may require tightening the spokes and pulling the rim one way while other areas may need to be loosened to allow the rim to move back the opposite way. Take your time and make small changes as you go. As I mentioned before, it doesn’t take much to see a significant change in rim location as the spokes are tensioned.

As the rim is fine tuned for side to side runout, the pointer can be moved closer to reduce the gap. Reducing the gap as the rim is trued will make it easier to see smaller differences in runout. To really fine tune things I like to use a dial indicator, setting the contact point up on the outer edge of the rim. Again, this isn’t absolutely necessary and similar accuracy could be achieved with a simple pointer.

Here I’ve snapped photos of the high and low points on the rim. The total runout is the difference between the high and low points. In the left picture the needle is 0.0075” (0.19mm) to the left of my zeroed point. In the righthand picture the needle is 0.008” (0.20mm) to the right of the zero. This gives me a total runout of 0.0155” (0.39mm). Most service manuals suggest a max runout of 0.079” (2mm) so I’m well within spec! Quite frankly I was very pleased to get the rim to 0.0155” since the rim is old and slightly dinged up.
The rim I was working on is centered on the hub. Some rims will be offset and it will be more important to pay attention to the relationship between the edge of the rim and a feature on the hub (usually the brake disc machined surface or the machined surface for the sprocket). Your service manual will provide specs for measurement points and specify how much offset should be present. Setting the offset correctly is important because if the offset is off, the front or rear wheel will not be inline with the other wheel. This can make the bike's handling very interesting! I don’t think a little misalignment is too noticeable on dirt, but it is definitely a problem on asphalt.

A straightedge can be used to measure from the indicated surface, outer edge of the sprocket, or brake disc to the edge of the rim. If measuring off the sprocket or brake disc, you’ll need to subtract the thickness of the sprocket or disc from your measurement.

If the rim is not quite positioned right after all the side to side runout has been corrected, it can be shifted at this time. To pull the rim one way or the other, simply evenly tighten all the spokes on the side you are trying to pull the rim to. The opposite side spokes can also be loosened to help allow the rim to shift over. Once the rim is set where it needs to be, half the battle is over!

Next, the radial runout must be corrected. To do this move the pointer so that it sits past the outer edge of the rim.

The gap between the pointer and outer edge of the rim will be monitored and tweaked to achieve evenness throughout the rotation of the rim.
This time to induce change in runout, all the surrounding spokes in the area will either be tightened or loosened evenly in unison. To increase the gap, as I’m doing in the following photo, all the spokes are tightened which pulls the rim inward, enlarging the gap between the pointer and edge of the rim.

To decrease the gap in a specific area all the spokes in that area can be loosened allowing the rim to expand outward towards the pointer. Just like with side to side runout corrections, the nipples only need to be turned an ⅛ to a ¼ turn to make noticeable changes in the gap.

As long as all spokes in the affected area are tightened or loosened evenly, the side to side runout will not be affected. Slowly rotate the rim and make the necessary tweaks until the gap between the edge of the rim and pointer is close to the same as the rim rotates around. The pointer can be moved closer and closer to refine the roundness of the rim. The surface of my rim was too beat up to take accurate measurements so I simply relied on eyeballing the gap to set its roundness.

Once the rim has been trued both axially and radially, the spokes will still be relatively loose. The spokes will all need to be tightened gradually and evenly so that all the efforts of truing the rim are not wasted. Since the majority of rims are either 32 or 36 spoke rims every 4th spoke around the rim can be tightened. This results in an even 8 or 9 step pattern which is repeated four times to tighten all the spokes. First all the red spokes are tightened, then the greens, yellows, and finally blues. Tighten each spoke ¼ turn at a time.

Alternatively, forum member ballisticexchris, suggested a pattern where every third spoke is tightened. This would allow the tensioning of both sides of the rim within the same revolution of the wheel. I've always had good results with the pattern I've outlined but believe his suggested pattern will work equally well and is another option for you to use.

As the spokes are tightened, not surprisingly, the nipples will become harder and harder to turn. The evenness of the spoke tension can be checked by tapping the end of the wrench against the center of the spoke. The spokes will emit a ringing sound and the pitch will be different for spokes which aren’t the same tightness. Continue to work your way around the rim gradually tightening the nipples until all the spokes are similarly tensioned.

Next, use your hand to squeeze the spokes which are parallel to each other together. Squeeze all the spokes evenly around the rim. Squeezing the spokes will help gauge the tension, ensure the heads are fully seated, and help relieve stress built up in the spokes.

After squeezing the spokes together, check the tension in the spokes one final time. Most spokes should only be tightened up to 6Nm and the rim I was working on called for 2.2Nm of torque. A spoke torque wrench is the appropriate tool to use to set the final torque of all the spokes, however I didn’t have one on hand and some of you may not either. Instead I based the final spoke tension on how the new spokes felt in relation to a previously laced rim. This method worked okay, but it is always best to use the right tool for the job.

After you’ve finished tightening all the spokes it is never a bad idea to check runout both axially and radially one final time to confirm the rim hasn’t shifted. As long as the spokes were tightened evenly, changes in runout should not be an issue. Once you have checked runout one last time you are all set to install a new rim strip and put on the tire.

I hope you enjoyed this two part series on building and truing rims. Now that you have the info to feel confident building your own wheels from here on out, and are able to save some cash in doing so, go for it!

Just a heads up, you've got only three more days to use the thumpertalk2015 discount code on The Four Stroke Dirt Bike Engine Building Handbook (eBook) and get 20% off. If you love working on your engine and bringing your four stroke to its highest state of tune, then you are going to love the in-depth precision engine building knowledge I am providing for at-home mechanics and experts in this fully illustrated eBook. The eBook comes in PDF format, is sent immediately to your email inbox, where you can read it or print it off, and bring it into your workshop. To grab your copy and use the thumpertalk2015 discount code before it expires, click here.

If you have tips and tricks pertaining to wheel building, I’d enjoy hearing them. Please leave a comment below!

-Paul Olesen
DIY Moto Fix - Empowering And Educating Riders From Garage To Trail

## How To Properly Replace And Install Spokes On A Dirt Bike Wheel

How many of you become disheartened when spokes break, bend, or a rim becomes permanently damaged necessitating a rebuild of the wheel? I know a lot of people think rim building is a black art and are willing to shell out serious dough to avoid the job altogether. This week I want to debunk the black art of wheel building and provide you with an overview of the process, allowing you to take on your next wheel build yourself. Next week, I’ll cover the second half of the project by showing you how to true the wheel.

As you can see I have a great example of a wheel assembly that is way past its prime. The spokes are bent, loose, and the nipples are mostly all stuck. On top of that, the rim is cracked in a couple spots necessitating further repairs.

Before getting started disassembling the wheel, measure the distance from the rim to the ground. When the wheel is built the rim will need to be blocked up at approximately this height. Blocking the rim up will make the wheel much easier to assemble.

The spokes will be offset from one another. Often times this offset necessitates the use of different length spokes. The spoke kit I received came with two different length spokes and there was no indication of which went where. If there are no instructions provided with your spoke kit and your wheel features spokes of different lengths you will need to determine the correct layout of the spokes. This can easily be done by removing two of the old spokes, measuring them, noting their lengths, and positions.

Once you have determined the spoke length you can go to town cutting the rest of the spokes out of the rim using a cutting wheel or other suitable tool.

Remove all the old spokes, then closely inspect the rim for damage. On my rim I had two nice size cracks I had to deal with.

Once the rim has been replaced or repaired, preparations for lacing can begin. Since the wheel will be exposed to dirt, mud, water, and whatever else nature throws at it, I like to coat all my spokes with anti-seize before assembly. The anti-seize will provide a little extra protection against corrosion and help keep the spokes turning freely for a long time.

Separate the spokes according to their lengths so that there is no confusion during assembly.

Next, center the hub and block up the rim. Refer back to the measurement you took to establish the correct block height. As long as the rim is not offset to one side or the other it will not make a difference whether you start with the sprocket or brake side.

The outside spokes will be laced first. If you try the inside route you will quickly find that maneuvering the outside spokes into position won’t be possible. Simply install a spoke into its corresponding hole in the hub then align the spoke with its corresponding hole in the rim. The rim may require some rotating to align the spoke with the correct hole in the rim, however it will be glaringly obvious where the spoke must go since the holes in the rim are all angled.

As the spokes are installed, thread on nipples to retain the spokes. Only engage a few threads as you install the nipples. Keeping the rim loose will allow all the spokes to be installed easier as you go.

Once all the outside spokes have been laced in one side, lace all the inside spokes on that side. Don’t be afraid to pull the rim a little bit from side to side to help generate enough clearance so that the end of the spoke can easily pass through the hole in the rim. The rim may also have to be moved up and down a little bit to help center the spoke.

Next, flip the wheel over and begin lacing all the outside spokes on the remaining side. Pulling the rim from side to side and up and down will be necessary to get all the spokes aligned with their respective holes. By the time you are finished lacing you should have a nice fresh wheel assembly.

A good way to check to make sure the spokes have been installed correctly is to compare the thread engagement on each spoke. With all the nipples tightened only a few turns the remaining threads showing on the spokes should be about the same. If the remaining thread length is vastly different between the inner and outer spokes there is a good chance the spokes have been installed incorrectly. If this is the case, the longer spokes will need to go where the shorter ones currently reside to even things out. If this isn’t done, there is a good chance some of the spokes will run out of threads when the spokes are tightened.

After the wheel has been laced, the nipples on all the spokes will need to be tightened. Tightening of the nipples should be done evenly and gradually. An even pattern can be used to tighten the spokes so that the rim does not become offset radially in one direction. Most wheels either feature 32 or 36 spokes. Every 4th spoke can be tensioned to create an even 8 or 9 step tightening pattern. Once this pattern is completed, the next spoke in the sequence can be tightened and the whole process repeated until you have worked through all the spokes. In the picture below all the red arrowed spokes are tightened first, followed by the greens, then the yellows, and finally the blues.

As the nipples are tightened, checking for evenness among the remaining threads is a nice way to gauge symmetry. You may find that there are small differences between the inner and outer spokes in relation to the remaining threads left on them. Instead of comparing the inner and outer spoke threads to one another, only compare similar length spokes as you work. The more care you take to ensure the spokes are tensioned evenly now, the less work it will be to true the rim later on.

Check to make sure that the heads of the spokes fully seat in their holes in the hub. Some heads may get hung up and will require a tap with a punch and hammer to seat them. Relying on the nipple to pull the head into position doesn’t always work well.

Another sign that the job has been done properly is that the spokes will not pass through the ends of the nipples.

At this point you should have a rim that feels tight, is tensioned evenly, and is ready for truing. Check back next week for a write up on the truing process!

If you found this post beneficial and enjoy tackling projects yourself, you may find my eBook, The Four Stroke Dirt Bike Engine Building Handbook a great read. The book is packed full of in-depth precision engine building knowledge, a detailed overview of performance part selection, and many photographic examples which outline what to look for in problematic parts during a build. The eBook comes in PDF format, is sent immediately to your email inbox, where you can read it or print it off and bring it into your workshop. Right now we have an awesome deal running where all website visitors get 20% off when they enter the discount code thumpertalk2015 before purchasing. To learn more about the book, check out the Table of Contents, and read some testimonials, click here.

Do you have any helpful tips you want to add? Please leave a comment below and share your experiences!

## How To Repair Your Clutch Basket Dampers For Less Than \$30

How to repair your clutch basket dampers for less than \$30? Most modern clutches incorporate rubber dampers which help reduce torque fluctuations through an engine’s drivetrain. Single cylinder engines (four-strokes especially) have high peak torque fluctuations since they only fire once every fourth stroke. The dampers situated between the clutch driven gear and clutch basket help smooth out the delivery of power to the gearbox and rear wheel.

The rubber dampers wear out from normal use and in most cases can be replaced. Replacement of the dampers is a fraction of the cost of buying a new clutch basket, does not require a lot of special tools, and you aren’t out anything if the project doesn’t go as planned.

Before I get into the details of replacing the dampers, you are probably wondering how you can tell the dampers are worn out. When the engine is running some additional gear noise coming from the clutch may be noted, but honestly this is a problem difficult to diagnose when the engine is together. Finding this problem is much more likely when servicing the clutch pack or performing other work on the engine.

The easiest way to determine if the dampers have worn is by trying to rotate the clutch gear independently from the clutch basket. Depending on how worn the dampers are this may take a little bit of force, so it is best to lock out the clutch gear and primary drive gear. Once locked, the basket can be rotated back and forth to check for free play. Alternatively the clutch gear can be clamped in the soft jaws of a vice while trying to rotate the basket back and forth. The clutch basket should not move independently from the clutch gear.

In the first photo note the alignment marks are perfectly aligned. In the second photo the marks have shifted about an ⅛” (3mm). This may not look like much, but it will feel like a lot when you twist the basket.

In order to replace the worn dampers the clutch gear will have to be removed from the clutch basket. Rivets are used to secure the gear to the basket and the rivets will have to be drilled out in order to remove the backing plate, gear, and dampers. Once the rivets have been removed, the old holes can be tapped and bolts installed to secure the gear to the basket.

Prior to starting this project you’ll want to make sure you can source new dampers for the clutch basket. Aftermarket clutch manufacturers often offer replacement dampers for their clutches which can work equally well in a stock basket. Hinson, Wiseco, and others supply “cushion kits” which can be purchased from their respective websites, through Ebay, Amazon, or anywhere else you may like to do your motorsport shopping.

Before attempting to dismantle the clutch basket, check to see how much clearance is between the rivets and other features on the engine. Usually the idler gear will be the closest in proximity to the rivets. If the engine has an oil pump gear driven off the clutch, the oil pump gear may also be close to the rivets. Make a mental note of the clearance for future reference. The clearance between the parts when using bolts should be roughly equal to the clearance between the parts when the original rivets were used.

How successful you are at removing the old rivets will in large part dictate the size of the new bolts required. I made a couple of mistakes when repairing my clutch basket, so I ended up using bolts larger in size than I intended. The first mistake I made was a very silly one in hindsight. I didn’t realize that on this particular clutch the rivets are countersunk. Anytime countersunk rivets are used, grinding their heads off won’t work.

Instead of grinding, the rivets should be drilled from the back side. Use a center punch to help get the drill bit started on the right track.

Start with a small bit to create a pilot hole. Once the pilot has been created estimate the diameter of the rivets and select the corresponding bit size.

The diameter of the rivet can be deceptive since both ends have been mushroomed. Most rivets will either be 5 or 6mm in diameter. Err on the safe side and start with a 5mm (#9 bit) before moving up in size. This way if everything is done correctly a 6mm x 1.00 tap can be used to thread the holes. I made the mistake of thinking I was dealing with 6mm rivets so I drilled my holes larger than necessary leaving me with no option but to use an 8mm x 1.25 tap and large 8mm bolts.

Once all the rivets have been drilled, the backing plate can be removed and the rubber dampers will expose themselves. At this point it should be easy to see how the dampers have deformed and no longer fill in the holes properly. The dampers can be directional so take note of the orientation of the dampers at this time.

The dampers may also show signs of cracking and other damage.

Next, you’ll want to determine what bolts to use to secure the gear and backing plate back onto the clutch when it comes time to reassemble the clutch basket. Bolt size will strictly depend on the hole size you drilled to in order to remove the rivets. Ideally, the bolts will only be slightly larger than the original rivet, as this will allow for the easiest clearance between the bolt head and the idler gear. Keep in mind the following tap drill sizes for common metric bolt diameters and thread pitches.

6.00mm x 1.00 - #8 drill bit

7.00mm x 1.00 - letter “B” or 15/64” drill bit

8.00mm x 1.25 - letter “H” or 17/64” drill bit

The bolt head type will come down to your given clearance requirements between the backing plate and idler gear. You may find that a countersunk or button style head will work well. A great resource for selecting fasteners is at McMaster-Carr. If you’ve never explored McMaster-Carr you’ll quickly come to find that they sell just about everything under the sun and if you’re not careful you may part with more money than you originally intended! A few other good sources for metric hardware include Ebay (simply type in the bolt type you’re searching for in the search to turn up lots of results), Maryland Metric, and Boltnet.

For my basket I chose an 8mm x 1.25 Grade 12.9 socket head button which was 14mm long. Once the bolt has been selected, the backing plate and basket can be modified to suit. Start by enlarging the backing plate so that it will accept the bolts.

Once the backing plate has been drilled, if necessary, drill the basket rivet holes to the correct size so that the holes can be tapped. Be very careful when centering the drill bit in the hole. The more precise you are in this step the better the backing plate holes will align. Since the bit may have wandered a little bit when drilling the rivets out, it may be impossible to get everything centered just right. This isn’t the end of the world and adjustments can be made to the backing plate to get it to fit correctly.

Once all the holes have been drilled, carefully tap them using an appropriately sized tap.

After all the holes have been tapped, carefully add a chamfer to the top of the hole. This will deburr the hole and remove any raised edges which may keep the backing plate from sitting flat against the bosses. A drill bit larger in diameter than the hole or a deburring tool can be used to deburr the edge of the hole.

Proceed to fit the backing plate to see how the holes are lining up. As you can see, my holes wandered quite a bit when I drilled them so my backing plate holes don’t align well with the basket holes. I’ve shaded in with blue marker where I need to elongate the hole in order for the bolt to fit. Make sure an alignment mark is added to the backing plate and basket since the hole pattern is no longer symmetrical.

I used a rotary burr to elongate the holes, however, a hand file will work just as well. It will require a little more elbow grease and take a little longer though. Deburr the backing plate to remove any burrs which may keep it from sitting flat against the clutch basket bosses.
After making adjustments to the holes, all the bolts should easily thread into their respective holes.

At this point the clearance between the bolt heads and gears can be checked. As you can see, my bolt heads are too tall and will need to be ground down once they are permanently installed.

Grinding the heads is not ideal, but it ended up being inevitable for my application. Any necessary grinding will take place after final assembly since there may not be enough engagement between the bolt and bit.

After clearances have been checked and everything is ready for final assembly, the parts should all be thoroughly cleaned to remove any metal debris stuck to them. The clutch gear and new dampers can be reinstalled. If the dampers are directional, make sure they are installed in the correct orientation.

Next, install the backing plate. Apply a permanent thread locking agent to the bolts. Then install all the bolts. The diameter of the bolt and grade will dictate how it should be torqued. For your reference with the locking agent applied, I torqued my Grade 12.9 8mm x 1.25 bolts to 30Nm. Follow this link to view guidelines for torque specs on other metric fasteners.

If you were successful in selecting a bolt that clears the gears behind the clutch then you can give yourself a pat on the back as your work is done! If you are using bolts which must have their heads shortened this can be done using a grinding disc, mill, or any other suitable tool. Remove material from the bolt heads slowly and take just enough away so that the head clears the idler gear and any other obstacles.

I ended up removing most of the head and won’t be able to tighten or loosen the bolts, however, I planned for this prior to grinding. Removing the bolts isn’t a great concern because other parts of the basket such as the fingers will wear out sooner than the dampers will.

In total this fix cost me just under \$30 and will prolong the life of my clutch basket. With this write up you should also be able to repair clutch baskets with worn dampers, save yourself money, and prolong the life of expensive engine parts.

If you have questions, thoughts, or want to share your experiences - leave a comment below!

Thanks for reading guys and have a great rest of your week.

-Paul Olesen
DIY Moto Fix - Empowering And Educating Riders From Garage To Trail

## Cast Your Vote For The Cover Of The 4T Dirt Bike Engine Building Print Book

We just got back the two cover design options for the print book version of The Four Stroke Dirt Bike Engine Building Handbook, and guess what? We are asking for YOUR help in choosing the design. We figured what better way to know what our fellow motorheads are going to like than to put it up to a vote. The two options are pictured below and whichever cover gets the most votes wins.

Cast your vote for Cover #1 or Cover #2 by leaving us a comment below. We are tallying up all the votes over the next five days and will have a winner by the end of the week!

For those who have been wondering when the print version of the book will be ready to order, stay tuned. You aren't too far off from getting a shiny new print engine building handbook sent right to your doorstep.

For those who want to get their hands on the downloadable and printable eBook version, we are still running the 20% deal for the ThumperTalk community. Be sure to use the discount code: thumpertalk2015 to receive 20% off your purchase. Grab your copy by clicking here >> The Four Stroke Dirt Bike Engine Building Handbook (eBook)

Thanks for your support and I appreciate your input on the cover design!

Paul

## The Four Stroke Dirt Bike Engine Building Handbook

I hope all of you have been getting out on your bikes and riding as much as possible now that spring is in full effect. For those of you in warmer climates, please don't remind me you have been riding year round without any additional layers, this only makes me jealous and forces me to seriously consider the thought of moving. I've been very busy the past month, but have tried to get a couple hours in on the bike every Saturday. There truly is no better therapy than going out and spanking the bike around after a long week of work!

I'm very excited to announce that the eBook I have been working on these last four months, The Four Stroke Dirt Bike Engine Building Handbook, is officially released. I want to spend a little time talking about what the book has to offer you as a dirt bike engine building enthusiast; I don't think you will be disappointed. Below is a snapshot of the table of contents as well as a few interior pages, just to give you an overall look at what this book covers for you.

What could this book possibly be about that other reference materials, like service manuals, don't already cover? I wrote The Four Stroke Dirt Bike Engine Building Handbook to be an all encompassing guide on engine building. Whether you are building a stock or performance engine, this book provides a specific framework for you to understand and use throughout the entire process. From the moment there is doubt about the engine's condition to the time the rebuilt engine is broken in, I give you a step-by-step guide to help you work towards a successful build. My aim was to create a definitive resource that hit on all the topics you may question as you proceed through an engine build, and teach you the how and why behind the way things are done.

I've been very fortunate to work with talented engineers and builders over the years. This book is a way to share the knowledge I have learned from them with you, a way to bridge that gap for at-home engine builders to enable you to be better equipped with the proper insight and information when it comes time to rebuild. Today's modern four-stroke dirt bike engines are fine pieces of engineering, are designed to exacting tolerances, and require a great deal of care and precision in order to keep them operating at their finest. If you don't work with engines on a regular basis or haven't been taught by a great mentor, there are a lot of subtleties which can be overlooked that I've written extensively about for you.

Throughout the book, engineering knowledge and practical experience are fused together to detail the how and why behind the way procedures are performed, parts are designed, and engine performance is affected. This is the most important and valuable aspect of the book, and it's something you won't find in any service manual. The book doesn't just tell you to bolt part A to part B, it teaches and explains the correct way assembly procedures should be performed and why it is necessary to do so. It also explains the intricate relationship between parts. For example, the interaction between the valve guides, seats, and valves must be understood in order to understand why valve seat cutting shouldn't be left to just anyone. Along with the practical building how and why, an entire chapter has been dedicated to detailing how performance parts affect engine performance. Within this chapter helpful suggestions are provided to aid you in choosing the correct components for your build, depending on your specific riding needs.

If you don't work directly with engines on a regular basis, it is hard to acquire practical experience when it comes to diagnosing problems and detecting abnormally worn parts. Not knowing what to look for when inspecting engine components can lead to improper diagnosis and assembly of an engine, which could still have bad parts in it. I have filled the book with as many photos and written examples of worn or damaged parts as I could so that you will know exactly what to look for when inspecting engine components as you proceed through the build process. This is invaluable practical knowledge, which only comes with experience, and is not something you will find in your service manual.

Now that you have a general feel for what the book is about you may have more questions. One I've been asked a few times now by friends and fans is how can you write a book applicable to all makes and models?

Believe it or not, the variations of dirt bike engine designs between manufacturers are in truth very minimal. Sure, there are physical and locational differences. One brand may use two camshafts while another uses a single cam, or one may put an oil pump on the left side of the engine while the other puts it on the right, but the overall layout of the engines and function of the parts are all similar. I did not write this book with the focus being on the little differences between brand X and brand Y. I wrote this book outlining specific techniques and inspection points applicable to every type of engine you will encounter. The function and the way components interact does not change just because they are physically different or located in different places. This is imperative to understand in order to get the most out of the book. To ensure I've covered the various ways parts interact and can be assembled, I've used two different engines throughout the book as examples and have provided specific instruction on how to deal with assembly differences that will be encountered across the Japanese and European brands.

If you have a thirst to learn more about how your engine works and a desire to correctly disassemble or assemble an engine to professional standards, you will benefit greatly from this book. Whether a complete beginner or a seasoned builder, with over 300 pages and 250 images worth of information, there is fresh and useful knowledge for everyone. There is also valuable material packed into this handbook that doesn't just pertain to the act of building the engine. I include instruction on diagnosing engine problems, sourcing and determining which parts to replace, using precision measuring tools, setting up your workshop, and additional tests and inspections that should be performed when preparing racing engines. If you just want to build your engine back up to stock spec, you are covered. If you want to go the extra mile and prepare a racing engine, you are also covered. In a way this book allows you to choose your own ending by giving you all the tools and knowledge you need to complete your build at whatever level you decide.

You can order the eBook for \$21.25 and it will immediately be sent to your email inbox. From there you can download it to your electronic device of choice to read or print. You also have the option to just view it online. I created a discount code just for the ThumperTalk community that gives you another 20% off the list price. Be sure to enter the code: thumpertalk2015 before purchasing and bring your total down to \$17. This is one tool you can add to your toolbox that won't wear out and break on you and can be used universally. Thank you for your support of DIY Moto Fix these last few months, and enjoy the heck out of the book!

For those interested in a printed version of the book, we are definitely working on it! To stay updated on when you can order a printed and bound version, sign up for our eNewsletter. We will be sending out an email within the next month to our subscribers detailing how they can order a printed version once we have everything squared away.

Thanks for reading guys and have a great week!

-Paul Olesen

DIY Moto Fix - Empowering And Educating Riders From Garage To Trail

## Precision Measuring For The At-Home Mechanic // Part 3

As we wrap up our final post on precision measuring for the at-home mechanic, I hope you have found this three part series on measuring helpful and informative. If you need a brush up or haven't gotten a chance to read Part 1 or Part 2, we compiled all three parts into a free guide for you. You can download your free copy by clicking here.

This three part series comes right out of the book I am writing, The Four Stroke Dirt Bike Engine Building Handbook. The eBook is set to launch at the end of April and as someone who has been following my Moto Mind Engine Building Series posts, I think you're going to love the in-depth knowledge and information provided in this upcoming book on four stroke dirt bike engine building. Pre-order is now available for the eBook and you can learn more by clicking here.

In this post I will be covering the final six precision measurement tools you have at your disposal. Each measurement tool in this post features a description of appropriate applications for the tool and a step-by-step tutorial on how to use it. This post is designed as a reference so that you can easily come back to it at any time as you become more comfortable using measurement tools during a rebuild.

PLASTIGAUGE

Plastigauge is one of the only measurement tools you won’t mind throwing away once you are done using it. Plastigauge is a measurement tool used to check the clearance between parts. The plastigauge consists of little strips of plastic which are inserted between two parts. Once assembled the plastic strip is compressed. The amount the strip compresses can be measured and correlated to a chart (supplied with the plastigauge) which defines the clearance for the measured compressed width of the strip. For engine building purposes plastigauge is ideal for checking clearances between engine components utilizing plain bearings. The plastigauge is a great tool for confirming clearance and measurements.

Another plus is that unlike most other measuring tools, plastigauge is cheap! Plastigauge is usually sold in an assortment of sizes which cover multiple clearance ranges. Plastigauge strips will come in different diameters and each diameter will be capable of measuring a certain clearance range.

Where to Use: Examples include cam to cam journal clearance, crank bearing to crankshaft journal clearance, and crank pin to rod bearing clearance.

Calibrating Plastigauge

Finally a measurement tool where no calibration is necessary. Just make sure you choose the appropriate size strip for your application. Also make sure the plastigauge is fairly new. Plastigauge does get old after awhile and using old plastigauge may not yield accurate results.

Reading Plastigauge

After the plastigauge has been compressed use a calipers to measure the width of the compressed strip. Record the width in your notebook. Then look at the clearance chart provided with the plastigauge to determine the clearance that corresponds to the measured width. Yes, it really is that simple.

How To Use

1. Clean the parts being assembled

2. Insert a small strip of plastigauge between the parts being assembled.

3. Carefully lower the mating part down onto the plastigauge. Take great care to lower the part straight down so the plastigauge doesn’t move.

4. Install the fasteners used to secure the parts together.

5. Tighten the fasteners to the torque value recommended by the manufacturer. Follow any special tightening patterns that may apply

6. Carefully loosen the mated parts. Again, follow any special instructions for loosening provided by the manufacturer.

7. Remove the part. Check to see which part, if any, the plastigauge has stuck to.

8. Use a calipers to carefully measure the width of the plastigauge.

9. Refer to the chart provided with the plastigauge to determine the clearance which corresponds to the measured strip width.

Tip: With a keen eye taper and out-of-roundness can also be spotted by using plastigauge. Keep an eye out for variations in strip width after it has been compressed for clues about the condition of the bore.

DIAL INDICATOR

A dial indicator measures variations in height by utilizing a plunger which travels up and down. As the plunger travels a dial gauge records the amount the plunger has moved. For engine building purposes a dial indicator is a handy tool to have when measuring valve lift and finding top dead center.

There are a wide range of dial indicators on the market. Choosing the best one for engine building may be daunting if you’re not familiar with them. There are two main features you want to look for when selecting an indicator. The amount of travel the indicator has and the resolution of the indicator. Choose an indicator with around 1.0” (25mm) of travel which has a resolution of 0.001” (0.025mm). This type of indicator will work well for engine applications.

In addition to the indicator getting a few accessories for the indicator will be beneficial. Most indicators are not sold with a base. Magnetic bases are really handy when setting the indicator up and provide a means of securing the indicator so it can’t move. Even when working with aluminum parts (ex. cylinder head) a magnetic base can be utilized by bolting a flat piece of steel to the aluminum part.

Dial indicators usually come equipped with rounded contact points which are ideal for measuring flat surfaces. Occasionally you may encounter a setup which requires a different contact point. A variety of contact points are offered for indicators and having an assortment never hurts.

Tip extensions are a must have if you plan on doing any deep depth work with the indicator. One situation which routinely requires a tip extension is when using the indicator to find top dead center of the piston. Tip extensions can be bought in multiple lengths.

Where to use: Examples include measuring valve lift, and finding top dead center.

Reading Dial Indicators

Reading a dial indicator is very similar to reading a dial calipers. The only difference is the dial indicator’s gauge face is equipped with a second smaller dial face. For an indicator with a resolution of 0.001” the small face is divided into 10 graduations. Each graduation represents a tenth of an inch. The outer dial face is divided into thousandths of an inch. Each time the outer needle rotates one revolution around, the second small needle tallies a tenth of an inch. This eliminates the need for the user to keep track of how many times the needle has gone around.

The total measurement is comprised of the number of tenths of an inch the smaller needle is indicating plus the number of thousandths the large needle is indicating. In the picture above the dial indicator reads _0.136".

For metric and other resolutions of dial indicators the reading process is identical to the above. Take note of the units and resolution and proceed to read the indicator accordingly.

Calibrating Dial Indicators

Checking and adjusting the accuracy of dial indicators usually can’t be done easily in one’s own shop. For dial indicator calibration the indicator would have to be sent to a calibration lab. Fortunately, the applications an indicator is used for when building engines doesn’t require the utmost accuracy so calibration is seldom a problem.

How To Use:

1. Clean the contact point of the indicator and the part which will be indicated.

2. Carefully set the indicator up so that it is fixed to a sturdy base which can’t move.

3. The amount of travel in each direction you will need depends on the specific application you are measuring. Consider the motion and travel of the part you want to measure and set the indicator accordingly so that it doesn’t run out of travel halfway through measuring. For example, when measuring valve lift you would want to engage the indicator so that around a quarter of the plungers travel has been used.

4. Square the spindle of the indicator being measured. The more square the indicator spindle is to the part the more accurate the readings will be. If the indicator is set at an angle to the direction of travel of the part the indicator will not read accurately. Keep this in mind and always try to set the indicator spindle as square as possible to the part being measured.

5. Zero the indicator by rotating the gauge face so the outer needle aligns with “0”. For example when measuring valve lift the zero point would be when the valve is fully closed. When checking runout the zero point may be a low or high point.

6. Move the part being indicated a few times returning it to its starting position each time. Check to make sure the indicator consistently reads “0”. If it doesn’t then carefully adjust the gauge face to realign the needle.

7. Once the indicator has been zeroed proceed to move the part being indicated and take measurements.

8. After measuring return the part to its original position. Occasionally an indicator can get bumped or something can happen during the procedure. This is a good way to confirm one last time that the indicator is still zeroed.

DIAL TEST INDICATORS

Dial test indicators are very similar to dial indicators, however their primary function is more as a comparative tool than a measurement tool. The main difference between a dial indicator and dial test indicator is the dial test indicator uses a contact point which pivots instead of a plunger that travels up and down. This pivoting action results in an arcing path instead of a straight up and down path. The test indicator is best suited for taking comparative measurements and zeroing runout. For engine building purposes this makes a pair of dial test indicators well suited for measuring the runout of a crankshaft.

Just like dial indicators, test indicators are made with different lengths of travel and different resolutions. The most suitable resolution for crankshaft truing and inspection purposes is 0.0001” (0.0025mm). Most test indicators with a resolution of 0.0001” will have a travel of 0.008” (0.203mm) or 0.010” (0.254mm) which will be suitable for crankshaft inspection.

The test indicators will require fixturing so having a pair of bases, stands, and clamps is necessary. Fortunately, the test indicators use similar mounting systems as dial indicators so if you have fixturing for dial indicators you are all set to mount the test indicators.

Where to use: Examples include crankshaft inspecting or truing.

Reading Dial Test Indicators

The gauge face of a dial test indicator is symmetrical. The face is divided into graduations based on the resolution of the test indicator. Each side of the face represents half of the total travel of the test indicator. Reading the gauge is simply a matter of determining how many graduations the needle has moved from its starting point to its ending point.

Calibrating Dial Test Indicators

Like dial indicators, calibrating dial test indicators is usually done by a professional calibration lab. As long as the test indicator is well cared for the need for calibration should be infrequent.

How To Use:

Since the contact point of the test indicator travels in an arc the way the indicator is set up has an impact on measurement. This is the main reason test indicators can’t be relied on heavily for taking measurements and instead are used for comparing.

1. Clean the contact point of the indicator and the part which will be indicated.

2. Carefully set the indicator up so that it is fixed to a sturdy base which cannot move.

3. Most test indicators function best when the contact point is perpendicular to the direction of travel of the work piece. Some indicators differ slightly and should be set at a slight angle, so confirm with the instructions supplied with your test indicator to attain the correct orientation.

4. The majority of test indicators work best when the contact point is preloaded. As a rule of thumb a 1/10 - ¼ revolution of the needle is about right for setting preload. Instructions supplied with individual indicators may have specific preload instructions.

4. Rotate the part to find the high or low point. Zero the indicator by rotating the dial face so the needle aligns with “0”.

5. Move the part being indicated a few times returning it to its starting position each time. Check to make sure the indicator consistently reads “0”. If it doesn’t then carefully adjust the gauge face to realign the needle.

6. Once the indicator has been zeroed proceed to move the part being indicated and take measurements.

7. After measuring return the part to its original position. Occasionally an indicator can get bumped or something can happen during the procedure and this is a good way to confirm one last time that the indicator is still zeroed.

TRANSFER GAUGES

Transfer gauges are measurement tools which don’t yield a direct measurement. They are simply tools which can be used to transfer the dimensions of something requiring measurement to a measurement tool. There are two types of transfer measurement tools commonly used in engine building, small hole gauges and telescoping gauges.

Transfer gauges can be tricky to use accurately for a couple reasons. First, they introduce a second source for error. Instead of taking a direct measurement the measured part must first be sized using a transfer gauge. Then the gauge must be measured by a measurement tool such as a micrometer. It is easy to see how mistakes can accrue in this situation. Second, transfer gauges rely heavily on feel to obtain accurate measurements. If the user of the gauge is unskilled, the transfer measurements could be all over the board.

Taking these points into consideration transfer gauges can still be incredibly helpful when measuring engine parts. Transfer gauges are one of the most relied on methods of accurately measuring internal diameters.

SMALL HOLE GAUGES

Small hole gauges are used to transfer internal measurements usually less than ½” in diameter.

A small hole gauge has a split in its head which allows the head to expand or contract to the size of the part being measured. An adjustment knob at the end of the handle is turned to expand or contract the head. The head on the gauge can either be a full or half sphere design. The half sphere designs have the advantage of being able to measure blind holes.

Small hole gauges are usually sold in sets capable of measuring from around 0.125 - 0.500” (3.175 - 12.4mm). Each set is comprised of around four gauges with each gauge being able to measure a certain portion of the set’s total range. For engine building purposes, small hole gauges are primarily used to measure the inner diameters of valve guides.

Where to use: Valve guides

How to use:

1. Clean the bore of the part to be measured and the head of the small hole gauge.

2. Slowly turn the adjustment knob on the gauge expanding the head of the gauge inside the bore of the part being measured.

3. Simultaneously, gently rock the gauge back and forth and fore and aft inside the bore until the head of the gauge just starts to drag on the bore of the part. As you rock back and forth make sure the handle of the gauge passes through the point where the handle is square to the bore.

4. Remove the gauge.

5.Use a micrometer to measure the diameter of the gauge to determine the diameter of the part’s bore. Since the gauge can easily be compressed little to no pressure can be applied by the measuring faces of the micrometer.

6. Slide the gauge back and forth and fore and aft as you delicately tighten the ratchet or thimble of the micrometer. An accurate reading will be obtained when the micrometer just starts to drag against the gauge. Remember to measure perpendicular to the split in the gauge.

7. Lock the the spindle of the micrometer and read the micrometer to obtain the bore diameter.

Hot Tip: Since this is partly an exercise of feel, take multiple measurements until the measurements start to yield the same results. This way you can be certain the measurements are accurate.

TELESCOPING GAUGES

Telescoping gauges are the big brothers of the small hole bore gauges. Telescoping gauges are shaped like a “T”. A tightening knob is situated at the handle end and it controls one or two spring loaded plungers (dependent on gauge type). Once the knob is loosened the plunger(s) expand outwards to capture the diameter of the bore being measured. The plunger ends are convex so the gauge can be rocked back forth to obtain the measurement.

Telescoping gauges are usually sold in sets capable of measuring from around 0.3125 - 6.0” (8 - 152.4mm). Each set is comprised of around six gauges with each gauge being able to measure a certain portion of the set’s total range.

Where to use: Examples include lifter bucket bore and cylinder bore.

How to use:

1. Clean the bore of the part to be measured and the ends of the plungers on the telescoping gauge.

2. Set the gauge inside the bore with one plunger touching the side of the bore.

3. Slowly loosen the adjustment knob on the gauge handle expanding the plungers of the gauge inside the bore of the part being measured.

4. Set the gauge up so that the handle is just out of square with the bore.

5. Tighten the adjustment knob down.

6. Gently wiggle the gauge back and forth while passing the gauge through the bore. Only pass the gauge through the bore once. This will center the gauge and set the plungers to the diameter of the bore.

7. Clean both measuring faces.

8. Use a micrometer to measure the diameter of the gauge to determine the diameter of the part’s bore. Since the gauge can be compressed, little to no pressure can be applied by the measuring faces of the micrometer.

9. Slide the gauge back and forth and fore and aft as you delicately tighten the ratchet or thimble of the micrometer. An accurate reading will be obtained when the micrometer just starts to drag against the gauge.

[series of pics showing measurement direction

10. Lock the the spindle of the micrometer and read the micrometer to obtain the bore diameter.

Hot Tip: Since this is partly an exercise of feel, take multiple measurements until the measurements start to yield the same results. This way you can be certain the measurements are accurate.

V-BLOCKS

A V-block is a large precision machined metal block with a V in it. During an engine build V-blocks are used primarily for checking runout of cylindrical parts such as the crankshaft.

When shopping for V-blocks a precision ground matched set should be purchased. Fancy versions may come with magnetic bases, multiple Vs, clamps, or rollers. While some of these features are nice they certainly aren’t necessary and add to the cost.

That wraps up our three part series on precision measuring for the at-home mechanic, thanks so much for reading! If you would like all this precision measuring information in one place so you can come back and easily reference it, we created a free guide for the ThumperTalk community that you can download right to your computer or phone. Click here and I'll email the The At-Home Mechanic's Guide To Precision Measurement right to you so you can have it organized in one place.

If you are interested in owning a copy of The Four Stroke Dirt Bike Engine Handbook, pre-order is now available and you can learn more by clicking here.

Thanks again for reading and feel free to leave a comment below!

-Paul Olesen

DIY Moto Fix | Empowering And Educating Riders From Garage To Trail.