need help 2006 yz450f timing

Need help guys i have 06 yz450f with 480 big bore kit and when i try to put in time i line marks up on cams exhaust at 9 and intake at 3 with engine at top dead center and even did straw trick to make sure was at top dead center and when i turn engine over exhaust valves hit the piston, rechecked valves are out of tolerance no lash, think vavles need to be shimmed? what size shims come stock?

Edited by yz450ltd

There is no "standard" shim size.  Each valve is independently clearanced at the factory using shims in .01mm increments.  Most of them end up between 1.75 and 1.90.  If you actually have zero clearance, you will need a valve job.


Your timing should look like this:



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