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YZ 250F valve shim problem

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I had a very strange occurrence with a under bucket shim removing itself from its position on top of the valve inside its holder to become wedged outside of of the holder preventing the inlet valve from closing.. Luckily my son stopped the engine when it started to. "Tick" and the valve stayed out of harms way, one of the collets even ejected itself into the void of where the shim should have been...

Any ideas on what as happened here??

The engine was being operated at low rpm at the time ( according to my son) , I'd really like to understand and prevent this from ever happening again

Cheers Kenny

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The easy test would be to replace the shim only and see what happens.

Barring that, I would replace the retainer, keepers, and valve in question.

 

You don't give year, times since last rebuild, any new parts in that area, so without that info, its a toss-up.

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Valve , spring, retailer , collets & bucket are being replaced .. Engine has 50hrs total : 2hrs since piston & ring change..

Assembling and then we will just cross our fingers !! ;)

Sent from my iPhone using Thumper Talk

Valve , spring, retailer , collets & bucket are being replaced .. Engine has 50hrs total : 2hrs since piston & ring change..

Assembling and then we will just cross our fingers !! ;)

Sent from my iPhone using Thumper Talk

2013 model

Sent from my iPhone using Thumper Talk

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If the shim was not correctly in place I'm guessing the engine would have been very low on compression??

It felt normal and clearances were all in spec upon assembly..

Thanks for your opinions !!

Just looking for an excuse to trade up to a 2015 ;)

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