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How to determine Valve Shim replacement if current gap is .000

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Hello all, I have a 2002 Honda CRF450R that I am trying to adjust the valves on. This is my first time adjusting a bucket valve system and need some advice.

 

When I measure the gap on both of the Intake valves the smallest feeler gauge I have .003 will not fit. If I am unable to determine what the current gap is how do I figure out the new shim size. I am guessing the gap is between .002 and .000. I have done alot of reading but unable to figure out how to figure it out if there is a zero gap. I want to do this myself instead of taking to a shop to save the money I don't have.

 

Your help is greatly appreciated.

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Your valves are pulling into the head you can check compression first and leak down test to see if there's actually a leak but chances are you will need new valves and seats

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You will have to assume it has zero clearance and then put the estimated shim size in. After putting in the proper shim measure the clearance again and adjust accordanly. For example if the existing shim is a 190 and recommended clearance is .20 you would put in a 170 shim. Unfortunatley if you have zero clearance on the intakes the valves are most likley wore out and will require replacement and the seats will have to be recut.  

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Hi Supr Sloguy.....your suggestion will work but I was hoping to avoid taking it apart and putting it back together just to take it back apart again and put it back together again! :( Sounds like that might be my only choice if I want to go the cheap way.

 

Hi sj186......Where do I find the values for the compression values and leak down? I have looked through the manual but haven't seen anything in the specs. How do I know what is within spec for compression or leak down?

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If you are qoing to reshim the engine anyway, the cam chain and cam, or cams will have to be removed in any case.

When removing mark the size and shim location. On the valves that are too tight. Install the smallest shim you have after measuring it. retorque the cam / caps and see what you have as a gap. Then just do the math.

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If you have zero clearance, it's time for a head re-build.

If you wait too long ( like11 years) to rebuild the head the LEFT INTAKE VALVE WILL BREAK, OR THE CAM CHAIN WITH JUMP, GUARANTEED! 

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You're compression range will not be in an owners manual but rather a service manual. The value depends on year and if an aftermarket high compression piston has been installed different years used different compression ratios. If you're going to try changing shims which I would before just tearing down after you remove the can is the best time to do a leak down test because it has no influence from the cam on the valves listen through the carb and the exhaust if you hear any air coming from either location you need new valves and seats period the leak down percentage should not be over 15-20%. If no leakage is heard at either place proceed with shiming it but beware some of the early Hondas had a hard titanium coated valve and once worn the take a beating and you can shim it and 5-10 hrs later you're back to a no clearance issue with the possibility of worse damage.

Sport after removing the cam

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If i remember right....the intake clearance is supposed to be .006...

 

 

So put in a shim .006 smaller and measure clearance. Just a guess and check deal really not complicated.

Edited by 4STK4LIFE
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If i remember right....the intake clearance is supposed to be .006...

 

 

So put in a shim .006 smaller and measure clearance. Just a guess and check deal really not complicated.

 

The best way to do it.

 

You probably need new valves and seats tho, but if you had a race or something coming up this weekend and didn't have time, you could shim it for a temporary fix.

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Hi Supr Sloguy.....your suggestion will work but I was hoping to avoid taking it apart and putting it back together just to take it back apart again and put it back together again! :( Sounds like that might be my only choice if I want to go the cheap way.

 

Hi sj186......Where do I find the values for the compression values and leak down? I have looked through the manual but haven't seen anything in the specs. How do I know what is within spec for compression or leak down?

 

You have to take it apart anyway......your valves are out of spec and need adjustment.  To recheck the clearance after you put in a new shim all you have to do is bolt the cam assembly back on....its only 4 or 6 bolts....

 

 

Do you have a manual?

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take out the shim thats in there and put in one thats smaller.  when your zeroed out its kind of a guessing game with the first shim.   and no your valves WILL NOT BREAK just bc they are zeroed out.

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Buy a hot cams shim kit. You can install smaller shims and recheck. Once you get to the smaller shims it is time for a valve job.

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Thanks for everyone's feedback. This was my first timing job on a bucket shim valve train and was a little nervous.

 

I was able to shim the left intake back to spec .006 and get the right intake back to .005. It was not that bad to do once you go through it once and have the tools and experience you need to do it again. I have not had a chance to do a leak down test but will work on that in the coming weeks. I am still unable to find the compression values for this bike in the shop manual also. If any one know what it is it would be appreciated.

 

Many thanks again to this great forum and group of users.

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Thanks for everyone's feedback. This was my first timing job on a bucket shim valve train and was a little nervous.

 

I was able to shim the left intake back to spec .006 and get the right intake back to .005. It was not that bad to do once you go through it once and have the tools and experience you need to do it again. I have not had a chance to do a leak down test but will work on that in the coming weeks. I am still unable to find the compression values for this bike in the shop manual also. If any one know what it is it would be appreciated.

 

Many thanks again to this great forum and group of users.

 

A compression test is kind tough. The reason is the decompressor will let the air out when you kick it through. If you disable the decompressor mechanism, you'll probably break the kicker off trying to kick it through. Assuming you leave the decomp alone, look for roughly 85-90 psi. Ya, it seems low...because the decompressor is letting all the air out, remember?

 

If you had one valve go to zero, its going to need a valve job sooner rather than later. In the future, you can find the initial shim spec on the bench. No need to assemble the thing entirely to get there. On thing to think about though, the clearance in the cam bearings allows the cam to flop over a little when the cam chain tensioner is tight, so when you take your bench measurements, if you want to be insanely anal about it, put some downward pressure on the drive flange fo the cam to suck up the bearing clearances and then take your measurements for the shims.

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