I pulled the right cover off last night to check the CB gear. The gear with the key in it was absolutely tight on the Crank. I could not move it in anyway at all. There was a little bit of play between the drive gear and the driven gear that sits on the shaft of the counter balancer but it was just play between the 2 gears not the drive gear on the crank, I assume this is normal. I'm going to check the valves tonight when I get home and inspect the chain. This bike is a 99' yz400 and I'd never heard of the CB Gear coming loose on this model in these forums but the noise that I was hearing sounded like what was explained in past posts. Khris ------------------ When in doubt, GAS IT!