Just joined the forum and would like to ask a few questions.

First, I bought a 2002 Quadrunner F250 at one of our pawn shops and it has been rode pretty hard. Most of the problems look like they are from a bad o-ring in the oil filter cover and they rode it with low oil. I.E. Noisey top end and slipping clutch. I'm going to leave the clutch for the pro's, but I think I can tackle the top end. After I broke into the valve cover, I didn't notice anything that would cause a clacking noise. No worn cam or rockers. There is some slight scaring at the end of the cam bushing area, but not major wear. I'm going to pull the exhaust today and replace that o-ring. Where do you think the noise is coming from? Piston slap, rod pin, or loose rockers. The noise goes away once you get to a cruising speed.

Second, I bought a rebuild kit off of ebay and o-ring look smaller in thickness than stock. Is this normal for these low cost kits. It's a K & S top end kit.

Hopefully I will be able to offer assistances as I educate myself more on ATV's.