sticky valve...or something

I have a 98 yz400. The left side intake valve has stripped the cotters on multiple occasions. I can't be sure if the valve is sticking and causing this or if the valve just becomes stuck as a result of being struck by the piston. each time this happens I replace the valve and inspect the cylinder head but can't find any visible defects. Bottom line......stripped cotters, stuck valve, valve bent from piston. Not sure in what order. Please help, this is driving me crazy.

By "cotters", do you mean the valve "keepers" ?

yes... the wedge type keepers

The forums are good for ideas, its hard for us to actually know for sure.

But i would think once you bend a valve (valve hits piston), the valve is shot, replace the keepers, replace the spring!, and DEFINATELY get a new valve guide installed.

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