why are my valves are hitting my piston?

Question

the valves only hit my piston when there is a quick pull on the throttle and sometimes when using the kick start but under normal riding conditions or even if I'm going fast they don't meet at all...the problem started when we installed high compression piston and lengthened the duration on the cams..the piston has been modified several times to put deeper grooves so that the valves can't reach the piston and all though there is a difference they still do hit each other

Answer 1

Have you tried indexing the cam or is the timing out by one tooth, your valve springs can also play a big part in the problem if they are weak they wont close the valves fast enough which is known as valve float and can be very destructive. Double check the timing as well. Good luck with that one!

Answer 2

You'll either have to keep modifying the pistons or get a cam with less duration. If the cam timing is correct, it's directly related to these two areas

Answer 3

A thicker head gasket will band aid the problem, but it will lower your compression a touch. It's that or a different cam, piston or connecting rod.

Answer 4

.The answer is obvious despite all your modifications you have not got enough clearance between your valves and piston tops.Altering the cam timing also will affect the problem you need to start again its tough but it wont cure itself

Answer 5

First, what bike and who made the parts? Is it a kit or from different suppliers? Someone screwed up when they put it together. You did fit the $400.00+ heavy duty valve springs?

Answer 6

try getting a thinker base plate gasket the new piston is too big

Answer 7

I agree with ilikecheezeb...