Thread: dirt bike rebuild, are there any tell tail signs when its needed?

They're pretty bullet proof those engines, especially in comparison to other brands. I wouldn't say they're particularly rattly. Re shim valves and check the cam chain isn't at the end of its adjustment. Try running on 95 or av gas if you're not already and see if that makes a difference.

I put over 200hrs on one of my YZ250Fs and never touched the head on it.

If it's still bad or rattly under power I'd be pulling it down and checking the main bearings, big and little ends. I'm OCD with engine rattles in MX bikes.