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New piston 06yz450f advice needed

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Hey all,

Saturday just gone a very good mate of mine crashed heavily at a weekend track we go to.

He broke his left femur, left ankle and right wrist, he got A LOT out of shape through a whoop section and charged the upcoming left hand berm in 3rd gear pinned struggling to get control of the bike.

The result was being thrown from the berm without the bike at least 25m.

I witnessed this from the start of the track, not knowing at the time that it was my good mate who just happened to be riding my 06yz450f.:censored:

The bike suffered a bent rear subframe, both radiators gone, both footpegs bent as, handlebars (high bend are now hands on your thigh bend), twisted triple clamps and iam hoping that the front forks arnt bent.

My question is, since the accident i decided to tear down the bike for a good clean and damage inspection. The bike has done well over 100 hours and i feel its the right time for a new piston and ring effort.

I am leaning towards a cp piston based on general feedback on the site and from a mate of mine.

Not having done this before do i need to do anything to the cylinder in preperation for the piston?

The middle intake valve has been shimmed once so iam thinking they are good for some more riding time.

What else would i replace if I am going to pull it down. (New gasket kit), anything else.

Any info, general tips much appreciated.

Luke

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The cylinder will need to be honed, preferably with a spring ball, or "bottle brush" hone. Be sure to create a good cross hatch in the bore at about 60 degrees to its axis.

The question on the valve is, how many hours since it was shimmed, how much was it changed at that time, and what is the current clearance? If it was changed by more than .05mm, and is not holding a steady clearance, it needs replacement. The hard coating on the faces is less than .02mm thick.

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Gray,

Can you elaborate a little more on the honing bit? I have always just used a wet sand paper (as per the manual), but I know that honing is better. I am about to replace my piston also and want to hone the cylinder. Can you give some more specifics, or even directions please.

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A spring ball hone, like the one below, looks roughly like a bottle brush with abrasive balls at the ends of the bristles. Any good auto parts outlet will have the hone, or can get one quickly enough. Better quality ones can be had through Snap-On, or other tool outlets. You need a cylinder hone with a slightly larger than bore size. The Brush Research hones are ordered by the bore size, and the oversize is built into it.

You don't need a drill press, but you do need a drill that will turn at about 500 rpm, and has the capacity to accept the hone shaft. A good 3/8" with a low speed setting should work. A 1/2" is better. Thoroughly wet the hone by dipping it in a can of solvent, mineral spirits, or kerosene and push it into the cylinder. Hold the drill in one hand, and the cylinder in the other, with room at the bottom of the cylinder for the hone to extend part way out. As soon as you start the drill, begin to run the hone up and down the length of the bore so that a third of it comes out at either end. Reverse directions without stopping, so that the hone is always moving along the length of the bore as it turns. You should make a pass to the bottom and back to the top at the rate of about one or two times a second. This will create the cross hatch pattern. Make only 4 passes down the bore and pull the hone free BEFORE you stop the drill. Check the cylinder. You should see that the entire wall surface has been refinished, leaving no untouched "shadows" or vertical scoring. If these are present, repeat the above procedure again, once. It should need no more than that. If the cylinder still shows vertical scoring or shadows near the top of the bore, it may be too far ffrom straight to be reused without being bored and replated, or replaced.

Remember to THOROUGHLY clean the cylinder afterwards. After you think it's clean, finish it with a white rag and ATF. Wipe the bore until the rag comes away clean.

A cylinder finished by another method may seat the rings without any difficulty, but one finished this way will seat with nearly absolute certainty, and very quickly.

21332.JPG

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Gray,

This is exactly what I needed to know. Thanks for taking the time to spell it all out in such plain language. You are the man, and your advice and knowledge is so appreciated.

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The question on the valve is, how many hours since it was shimmed, how much was it changed at that time, and what is the current clearance? If it was changed by more than .05mm, and is not holding a steady clearance, it needs replacement. The hard coating on the faces is less than .02mm thick.

The middle intake valve was shimmed 20 hrs ago and to my suprise when put the feeler gauge into it, it is still showing the same clearance.

I just got the cylinder off and the piston has 0 blow by. My mate works for a parts company so i can get the stock parts (OEM is it?) at cost.

Based on that what should replace at this point considering the machine has done a lot of work on the stock piston.

- OEM Piston and ring set.

- Gasket set

????? What else would you advice.

Do i need to replace any bearings?

Thanks Luke

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This should be the ball hone you would use. I believe I will get one but on the other hand I have herd it would be a waste of money cause I was told you can take a scotch brite pad with a little elbow grease and get the same effect.

However they didnt say which way to scrub with the scotchbrite pad. I assume you would just go up and down through the cylinder and around.

I have a 06 also and this would be the ball hone to use on ours.

http://www.enginehones.com/418240ao.html

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You could work for 3 hours with Scotch brite and not have the finish you would get in 3 seconds with the correct ball hone, nor would the rings be as likely to seat.

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the con rod bearing. (upper) the wrist pin will go through it
Without a quote, it's a little hard to tell, but it looks like you're answering the question as to what else is needed. But you should know:

  1. That question is over two years old
  2. There is no wrist pin bearing in a YZ450

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The cylinder will need to be honed, preferably with a spring ball, or "bottle brush" hone. Be sure to create a good cross hatch in the bore at about 60 degrees to its axis.

The question on the valve is, how many hours since it was shimmed, how much was it changed at that time, and what is the current clearance? If it was changed by more than .05mm, and is not holding a steady clearance, it needs replacement. The hard coating on the faces is less than .02mm thick.

Grayracer, you seem to know all things yamaha , so I don't want to question your answer, but... I was told that you couldn't hone a nikasil cylinder. I guess it would be ok to try, I mean after all what do I have to lose, I thought I had to send my cylinder off to be replated. Will this work if you can feel your score marks with your finger? Thanks!

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The risk in honing a plated cylinder would ostensibly be the removal of the plating from the bore, yet Nikasil is literally as hard as some abrasives are, and some will go so far as to say that Nikasil is too hard to be honed at all. Consider that glass can be scratched with abrasives that are not as hard as it is.

I bottle brush hone every cylinder I use, Nikasil or not, with the sole exception of new Yamaha cylinders, which are supplied with a proper finish on them already. My engines seat the rings almost immediately, use no oil, and last. The hone takes a beating, but that doesn't concern me. The finish on the cylinder does.

As far as the question of score marks go, you can use the hone to tell you whether the cylinder is usable or not. If the marks or wear shadows are still there after 4-5 passes up and down the bore with the hone, then the answer is no, the wear is likely to be deeper that the plating, and the cylinder rates at least a careful professional evaluation before reusing it.

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The risk in honing a plated cylinder would ostensibly be the removal of the plating from the bore, yet Nikasil is literally as hard as some abrasives are, and some will go so far as to say that Nikasil is too hard to be honed at all. Consider that glass can be scratched with abrasives that are not as hard as it is.

I bottle brush hone every cylinder I use, Nikasil or not, with the sole exception of new Yamaha cylinders, which are supplied with a proper finish on them already. My engines seat the rings almost immediately, use no oil, and last. The hone takes a beating, but that doesn't concern me. The finish on the cylinder does.

As far as the question of score marks go, you can use the hone to tell you whether the cylinder is usable or not. If the marks or wear shadows are still there after 4-5 passes up and down the bore with the hone, then the answer is no, the wear is likely to be deeper that the plating, and the cylinder rates at least a careful professional evaluation before reusing it.

Thanks again Grayracer!

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Can you use other types of hones besides a ball hone to hone a nikisil cylinder?
You can, but you shouldn't. Fixed stone hones attempt to impose a precise cylindrical shape to the bore. "High spots" must be removed enough to allow the hone to contact the low spots. A bottle brush has no such restrictions, and will refinish a cylinder of any shape without removing a significant amount of material in the process, if it's not scored too deeply. If the cylinder requires precision honing to correct its shape, it needs replacement or refinishing.

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I have torn down my engine and done a careful inspection of the parts. My cylinder/piston fit is well within spec, and the cylinder is also well within spec (taper, roundness, & diameter). The only thing I am going to change is the piston rings, which are getting somewhat close to the limit on end gap. Since I am only replacing the piston rings, how important is it to hone (de-glaze) the cylinder? I though I read in the factory manual that it said do not hone the cylinder. This thread seems to indicate that it is necessary for a good ring seat. Can someone explain why the de-glaze is important to seat the rings, and do I need to do this if I am only replacing the rings?

Thanks,

Scott

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