how many hours on top end

after how many hours should I rebuild my top end on a 2007 yz450 bike has been ran very hard and raced its whole life however is very well taken care of I have about 70 hours on it now shimmed my valves once but haven't done a top end yet when should I?

If you look in the service manual, which of course you own, it will give you range of hours that is recommended to change the piston (racing hours).


You should buy an inexpensive micrometer that will measure the bore and piston, so you can check service limits; then you will actually know when it's time, based on your measurements and hours run.

That way you can know when to do it, in hours, next time.


I would replace it now.


So in 7 years it's only run for 70 hours? 


I ride that much in 3 months....

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