What can cause a valve to fail?

Recently had headwork done on my 2001 YZ426 (new SS valves, guides, springs, etc). I've had it out a few times with no issues. Went for a ride last night and one of the valves snapped :ride:. Valve clearances were within spec according to the manual.

Just wondering what could have caused this. Any input is appreciated.

Thanks.

If the seats were not cut concentric to the valve guides then you will get a failure like this pretty quickly. If you did not use heavy enough springs to match the weight of the stainless steel valves then you will get valve float which could also cause this. If your cam jumped time you could have hit the valves into the piston and broke one off (though typically you will see another valve bent at least if this were the case). And then there is always the possibility that the valve was faulty from the factory.

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