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valves loosening


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Checked my valves and both my exhaust valves had loosened a bit... thought it must be carbon build up so pulled the valves and cleaned them and the head up...reassembled and they're still loose. I'll reshim to spec but I'm alittle puzzled, I thought they only tightened up not loosened? Am I missing something here??

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they loosen because the valve seat gets stamped and hammered. yes they usually do loosen... some rare cases they tighten, just spec them out and check in one ride then in three rides. If they are good at the three ride mark then they will be good for a while!

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I've always assumed that if the valve clearance reduces then the valve has "pulled up" due to wear on the back of the valve or the seat. eg. Engine been dusted. Reasonably normal.

And if the valve clearance increases, then something between the top of the valve stem and the cam lobe has worn. eg. poor or contaminated lubrication. Not normal.

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valves will normally tighten as valve and seat wears which pushes the valve higher up towards the cam , therefore you go smaller shims to get them back in spec .

Only thing I think of is the shim is wearing smaller or the cam lobes are wearing ( these 2 things happening would mean serious problems .

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Only thing I think of is the shim is wearing smaller or the cam lobes are wearing ( these 2 things happening would mean serious problems .
Exactly what I was thinking when the clearance increases. I would be concerned that something very abnormal has happened.
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