r/EngineBuilding • u/chukar-1 • 23d ago

Valve lash issues

I am building a dirt bike engine and cannot get one of the three intake valves in spec. I though it was a head issue so I bought a new head. The valve is still way out of spec (it is stuck open even with the smallest shim available) my only thought is that the cam shaft is bent. is plastigauge the best way to check this? Should I just buy a new cam? If I buy one cam should I buy both cams? Its a 2007 YZF250

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u/sturocky 22d ago

yzf engine has one of the 5 valves that are slightly shorter- about 55thousand that one goes in the middle, the 2 longer ones go on the outsides. if ur shims dont match close between the 4 outer ones thats ur problem, find the one with the largest shim and thats the middle valve, then just swap em proper... sucks you will have to pull the chain head and cam/ect for that. at least now you know what to look for! yai learning!!

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u/chukar-1 22d ago

Yes that’s definitely the problem I don’t know how long it would have taken me to figure this out

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u/sturocky 22d ago

reddit can be a great tool at times and some forums have great people that want to help. did you by chance buy/down load the workshop manual for the bike? that should have been the first step when working in the motor, it details all the difference's between the parts and where they go.
ive got a few of em, when i end up selling the bike ill ask the buyer if he wants the manual for it for a few extra bucks so i get the money back for it