will valve decarbonizing improve clearance?

2 replies to this topic
  • broncomoto

Posted November 27, 2010 - 10:17 PM


YZ450FV 2006

Both Exhaust valves are at .007 (tight) with 170 (from factory) shims.

One outer intake is at .004 (tight) with a 170 shim from factory

the other outer intake is at .004 (tight). 50 hours ago I shimmed it from the factory 170 to a 175

the center intake has no clearance with a 170 shim from the factory.

will decorbonizing get me back to specs (200 hours and never been done)?
Can I shim? and if so, how far?

finally, should I replace the piston and rings (it's not blowin' smoke...)


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  • sacfelix

Posted November 27, 2010 - 10:56 PM


If you have 200 hours on your bike and the center intake is zeroed out you probaly have cupping on the valve face and wearing into the seat. If your going to adjust the shims I would jump down 3 full sizes on the shims and then recheck. I dont know how long it will stay in spec. I dont think decarbonizing the head will get you back into spec either. You would have to pull the head check it out. If your going to open the motor up I would do the piston, rings, timing chain and rebuild the head. Make sure you also check the rod for play. I have an 06YZ450 as well and I went 246hrs on her before I did a rebuild. At this point your better off doing the rebuild and not waiting for the bike to need a new motor.

  • BBrown626

Posted November 28, 2010 - 08:21 AM


if there is carbon in there affecting clearances in the valves it would be holding the valve open. Holding the valve open would show up as increased clearance between the bucket and cam. Your valves are tight, so you have wear or you have debris holding your bucket up. I think the ladder is pretty unlikely.

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