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Moto Mind
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.


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What you really need to know about air filter maintenance

Posted by Paul Olesen , July 05, 2016 · 7,881 views

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.

 

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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.

 

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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.

 

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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.

 

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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.

 

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Thanks for reading!

 

-Paul

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TigerTanker
Jul 06, 2016 05:51 AM
I suggest greasing the flange. I have a funnel web, and on my first use I missed a good seal due to its large size and my lack of experience. Fortunately I laid down a fair amount of lithium grease and the opening that was bringing in contaminants had enough grease to trap the incoming particles. So....grease the flanges!

I think most folks over oil thier filters; myself included.  What I do is after I have the filter oiled I take several paper towels and wrap them over the filter and squeeze the excess oil out onto the papaer towels.  Or if you have time, hang the filter for a day.  After a day look at the oil gathered at the base of the filter and squeeze out that excess oil.

I really like the Filter Skins.  A simple to use, easy to clean condom for your air filter.  They really prolong the service intervals of the main filter.  

At the TT Store:  https://www.thumpert...6-p4124076.html

or

http://pcracingusa.c...bikes_p_57.html

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triple stitch
Jul 12, 2016 10:11 AM

No Toil oil/cleaner and Pro Seal airbox gasket all day!  Application with the aerosol can also minimizes over-oiling and reduces waste!

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P-Schrauber
Jul 13, 2016 01:35 PM

I' am a fan of any filter oil that can be washed out with any basic dish washer soap and warm water.

This is the easiest, cheapest, enviroment friendly and healthiest way to clean foam filter, further

more it's in my personal ´view too the best as you can flush the filter very good too.

The already mentioned NoToil oil is a very good option may be even the best for US, here in Europe some other brands like Motorex are very good too.

 

To the over oiled filters, I try to use as little oil as possiple as too much oil gloggs the foam, I use small plastic bags you get as freeze bags, they come in every size, I place some bigger drops to the filter, put it in the transparent plastic bag and gently squeeze the filter until every spot has the same color, exessive fliud will rinse down to the bottom of the plastic bag, that left over fluid can then filled in the oil bottle for next use again. Another benefit you have clean hands!

 

I just oil filters before I use them, as once applied they attract dirt and dust very well.

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Paul Olesen
Jul 19, 2016 06:43 PM

Thanks for the additional tips and comments!

About Paul Olesen

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