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yamaha491

Shim changes after Valve Job -

4 posts in this topic

I have an 06 YZ450F with 90 hrs of use and I decided to do a valve job. I sent my head off to have the valves seats machined and and new OEM valve components installed. I replaced all the shims to achieve the correct valve clearance and I ended up having to make a bigger adjustment on the intake side than what I would of expected. The stock intake shims were all 192's and I ended up with two 160's and one 165 (.0106in to .0125in from stock). Does this seem to excessive? Is there a service limit and if so how do I check with all the variables?

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Not at all uncommon. When valves are replaced, the seats are cut, theoretically, enough to provide a good seat. This machining 'tightens' the valve. sometimes, the valve stem will be shortened slightly to make the overall clearance in range. As long as it can be shimmed into proper clearance, you are fine.

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When i re-cut seats it's usually one shim size thinner, after a perfect seat.

Sounds like guy cut allot. Not a big deal, just lowers compression, reduces spring seat pressure. If they are cut MUCH deeper I'd be shimming the vavle shim to get seat pressure back.

1.90mm - 1.60mm = .3mm or .012 inches deeper. Not huge but a wee bit excessive. Seat pressure will still be fine.

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If they are cut MUCH deeper I'd be shimming the vavle shim to get seat pressure back.
You meant "shimming the valve spring" did you not?

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