Valve Inspection and Clearance Adjustment Limits

Hi guys.

I am in the process of adjusting my valve clearances by replacing a couple shims. I previously had a shop do it (last year). The tech told me that one of the exhaust clearances was tight and he fixed it. I recognize that shim because it is a 180 rather than a number I can't get at the shop. All the rest are the original shims and therefore my baseline.

So knowing most of my baseline, how do I know when I should stop shimming and address the wearing of the seating surfaces?

The bike is an '04 YZ450F.


Since the hard nitride coating on the valve face is so thin (<.001"), almost any wear at the valve face means trouble. If you ever find a valve that needs a shim 0.10 mm smaller than the original, you most likely need a valve job. The giveaway will be when you ride the bike one more time and find that it needs to be reshimmed again afterward.

Thanks Gray.

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