2007 YZ450F valve clearences


8 replies to this topic
  • ReedRulz

Posted January 24, 2010 - 12:10 PM

#1

I just got finished checking my valves and this is the first time i've checked them since having my motor rebuilt 25 bike hours ago. My question is all of my valve clearences where higher than there suppose to be. The 3 intake valves where .230mm to .280mm out. I thought the valve clearences where suppose to tighten not loosen. The two exhaust valves where only .05mm out. The funny thing is as far out as the intake valves where the bike would always start on the 1st or 2nd kick. What could cause the clearences to widen instead of shrink?

  • grayracer513

Posted January 24, 2010 - 01:18 PM

#2

One thing that can cause it is shoving the biggest feeler you can force under the valve in there, but presumably, you're not doing that.

You're saying that the exhaust valves measured .30mm, and the intakes were between .38 and .43mm?

  • ReedRulz

Posted January 24, 2010 - 03:00 PM

#3

One thing that can cause it is shoving the biggest feeler you can force under the valve in there, but presumably, you're not doing that.

You're saying that the exhaust valves measured .30mm, and the intakes were between .38 and .43mm?


I didnt shove the biggest feeler under the valve. I started with what the book called for and went up until the feeler wouldnt slide in smoothly. My intakes measured .381mm, .330mm, .356mm and my exhausts measured .254mm, .254mm. I think the exhaust valves are fine like they are, they're right at the wide spec. Intakes deffinatly need new shims. Just dont understand why the clearances are wider and not tighter.

Edited by mxr300ex, January 24, 2010 - 03:18 PM.


  • grayracer513

Posted January 24, 2010 - 08:16 PM

#4

The exhausts are wider than I'd like them, but they're OK. The only thing that would have happened to increase valve clearance that quickly over the length of the cam is a cam seizure, the cap being damaged, not bolted entirely down, or never set right in the first place.

You said it was just rebuilt, did you assemble it, or a shop?

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  • ReedRulz

Posted January 25, 2010 - 03:18 AM

#5

The exhausts are wider than I'd like them, but they're OK. The only thing that would have happened to increase valve clearance that quickly over the length of the cam is a cam seizure, the cap being damaged, not bolted entirely down, or never set right in the first place.

You said it was just rebuilt, did you assemble it, or a shop?


It wasnt a shop it was someone who does bike mechanic work on his own for a lot of the guys at the track.

  • grayracer513

Posted January 25, 2010 - 07:20 AM

#6

The one other thing that will increase valve clearance is bending the valves, but since it still has compression, you can rule that out. Reset them and look carefully at the cam cap in the process.

  • ReedRulz

Posted January 25, 2010 - 03:39 PM

#7

The one other thing that will increase valve clearance is bending the valves, but since it still has compression, you can rule that out. Reset them and look carefully at the cam cap in the process.


Thanks Grey. Am I just looking for scarring on the caps or can I check the thickness of the cap head with a micrometer?

  • grayracer513

Posted January 25, 2010 - 04:10 PM

#8

Checking clearance on the caps is done by first ensuring that there is no scoring, etc., on either cam or cap, then using a Plasti-Gage type clearance check. See page 4-26 of your manual.

  • ReedRulz

Posted January 25, 2010 - 04:26 PM

#9

Checking clearance on the caps is done by first ensuring that there is no scoring, etc., on either cam or cap, then using a Plasti-Gage type clearance check. See page 4-26 of your manual.


OK thanks a lot grey.





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