I was riding my 09 WR450 the other day on a very tough trail and it was constantly boiling over. After I was done with the trail I let it cool down and then continued to ride for about an hour with no problems. I was going down a hill and a rock high centered the bike and it fell over and died (walking pace speed). I re-started the bike and there was a very loud clicking noise coming from the engine that was related directly to the RPM of the engine. Rode it for a few hundred feet and it ran fine except for the noise. I did not see any exterior damage and it sounded like the noise may have been louder on the left side??? I turned it off and coasted down the hill and there was no odd noises. WHen I was loading up I started it again and the noise was still there. When I got home I tried starting the bike again and the noise was still there, but not as loud so may be related to engine temp? Several days later I pulled the skid plate and did not see any damage. Started the bike and it was still making the noise. It still sounded louder on the left side. Drained the oil and no shaving etc, I pulled the stator cover and everything looked normal, normal under the valve cover and normal after pulling the clutch cover. I pulled right side of the clutch case (kick starter, water pump etc) and it look good. Primary drive and counter balancer nut were tight. When turning the engine by hand I think I can hear a light ratteling noise, but its hard to tell. The only thing that stood out, and I dont know if this is normal, is when pulling on the flywheel it slides in and out and there is about 1/16in of play. Any ideas one what I should look at? I plan on tearing everything down till I find a problem, but it would be nice to have an idea of what Im looking for. thanks for any help.