Clarity for checking valves

I have an 01 426 that is YZ timed, and I think I'm gonna try checking/adjusting the valves myself.

From what I've read here it seems like I have to put the timing back to WR to check the valves because the references for TDC are different?

Also, if I choose to install an auto-decomp cam, do I lose the ability to run the YZ timing?


TDC is TDC, regardless of where the cams are timed. TDC is taken off the crank shaft. I put my engine at TDC before the valve cover is even off anyway.

So, to answer your question, no, don't have to change cam timing.

Use a YZ450F auto-decomp cam if you want auto-decomp. The WR450F cams are timed different to the YZ450F, meaning the auto-decomp is in a different position in relation to the cam lobe.

Checking valve clearances is easy, just follow your manual.

ok, but do the clearance specs I'm lookng for change when YZ timed?

Valve clearance specs are still the same for a YZ timed WR, or for a YZ;

0.10 - 0.15 mm intake

0.20 - 0.25 mm exhaust

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