Unforgiving tolerance the reason?

I checked my valve clearances yesterday (06CRF450R):

.005 Intake both sides

.010 Exhaust both sides

.024 decomp


At the bottom end of spec.


The allowed tolerance for Honda is so small there is hardly room for human error, let alone wear. The average human hair is .006. So, .001 either way is such a small amount I have to wonder if this is what is contributing to the "supposed" valve concerns with Honda. I forget the tolerances for Yammies, but I know my YZ allowed for much more. My experience with bikes are only the ones I've owned, so I don't know what to think about this. The CRF is a precision machine no doubt, but it would have been easy to measure the exhaust at .009 and then go out and buy shims. .001 is a barely measurable difference.

RHC, I would love to have your input on this.

I agree with you. It is a pain in the butt with those tolerances being so small. Though yours are OK I do not suspect they will move as much on the 06' due to the newer seat material. Be nice if there was a tool just for these bikes to take the guess work out of it.

It is my estimation that the true issue with the valves is really the intake system or lack there of. From the small/tight airbox

to the seals it invites issues with dust getting into the valve system. If they would make the airbox accessable riders may clean or replace their air filters as often as they should. :banghead:

I can feel a difference in power when my bike is at .006 on the intakes compared to .004 and .003. So yes it is that precise, but if you are at .005 I would just let it be, chances are if you take the cam chain off you will be able to slip a .006 in there with a wiggle of the cam shaft. Its when you can't get the .005 in there, then reshim.

Thanks guys.


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