i just got my quad out of the shop after a complete topend rebuild valves,valve guides,valve seats,piston,rings. In the first ten min of riding it just shut off and wouldn't start i took it back to the shop and they found that one of the exhaust valves were bent. i would be glad if any of u guys could tell me what would cause the valve to bend. one more thing they said the motor was timed properly so it couldn't have been the timing. thanks in advance for the help

 

Stock piston?

Stock cam (lift)?

High-compression pistons/high-lift cams, without adequate piston-top relief cuts for the valves, can produce interference--otherwise, hard to imagine how a true valve could become bent in normal service . . .

Foreign object bouncing up and down atop the piston?

I'd like to know the answer, too!

Tree Farmer

 

tree farmer it bored .20 over in the stock cylinder amd it has the stock cam

 

I agree with TF. The piston they used probably didn't allow enough clearance for the valves.