2001 Honda Foreman 450 ES
Did anyone ever hear rattling noises coming from your engine when going around 44 km/h and letting off the throttle a little? I just had to get a new piston, rings valve seals because the engine oil leaked out of the final drive shaft seal that comes out of the rear of the engine. The engine oil was disappearing and there were no leaks anywhere on the ground. Turns out it was leaking past the seal and directly into the rear swing arm's hollow tubing. When the guy took it apart the swing arm tubing has litres of engine oil in it. It was smoking really bad.
It runs great now but I can hear a slight rattle coming from the engine compartment somewhere. I can't hear it if I'm in neutral and rev up the motor but I can hear it when driving it around. Especially when on the road and giving it throttle. I thought it was the valve clearances. The mechanic set them to speck (.006) when he rebuilt the top end. I had him reset them again a little tighter to .005 but the noise is still there. Wondering if I need to break it in more or if there might be damage in the bearings (bottom end stuff). Hoping it goes away with break in. Any thoughts?

 

Kind of hard to say after a rebuild, and not being able to hear it. Anything out of spec could cause noise. Cam chain tensioner would be one possibility.

 

Recheck all motor mount bolts and any other nuts & bolts
It could be in transmission or drive system