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Discussion Starter · #1 ·
yesterday my bike wouldn't start and had very little compression, when i tore the motor down i found a bent valve (the smaller one) and small indent on the piston where it had hit the valve. any ideas as to what caused this? and to how i can stop it happening again as i have just ordered a trail bikes big valve head kit with domed piston ect and i dont want that to go the same way :cry: . the valves were gaped correctly and the spec of the motor was, standard head, kitico 88 kit with 20mm carb, kitico cam, kitico rev box, sano exhaust and tb manual clutch, running on sunoco race gas.

do the aftermarket rev boxes have any upper limiter? or could this have been the cause of the damage.



pics below but its hard to see the damage













 

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looks like its been hitting for a while, and finally just gave. if your getting a head, no worries.

is that the stock head? doesnt look like it.

is there anything youve changed lately?
 

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i think your pistons been topping out on the head too. have your engine been pinging or kknocking?

your motor might have overheated, u dont have a oil pump right?

im going to say it overheated and your valve warped.
 

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Looks like you were floating the valves for a while and the valve finaly hit the piston. I did the exact same thing, swapped out the head and installed some XR70 valve springs and problem solved . In you case the TB head will fix your problems.
 

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How was the cam timing ? Did the marks line up properly as per the service manual ?

You should think of getting a stronger cam chain when you put on the hypo head :wink: . If you have the stock one in it now , it may be stretched ???
 
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