I have an 2007 Foreman 500 that i just put a crankshaft w/ rod in and all new bearings,piston,rings, gaskets. It has a light knocking sound coming from the lower portion of the engine. It will make the sound whether atv is moving or not. The last time i rebuilt it i put a new wristpin and piston and rings and it made the same sound. I took off the front cover to check the clutches, everything seemed to be ok. I need some opinions please help. thank you.

 

check out your cam, pushrods, rockerarms, and even valve clerances. i know you said it comes from the bottom of the engine, but in my experance a tapping sound in a pushrod engine is cam to valve problem.

 

ok i will check that. Thank you.

 

Also check or replace cam chain tensioner.