Cam sprocket, valve help

[Vumad]

I have a 2002 warrior 350. I was riding at the track when I lost power and got a bad engine rattle. I took off the valve covers and found the lock nut on my exhaust valve had come off. I believe the nut was the rattle, and the screw backing out was the loss of power. I bought a new screw and nut and placed them in. My understanding was the exhaust asjustment for the warrior was 0.006-? so I adjusted it to 0.007 TDC cold. I checked the compression and got 155psi on my old guage. The quad seemed to idle well. It sounded to me like it had a bit of a puffing sound that didn't seem normal (don't know how else to describe it). It seemed to respec correct, so I took it on the street. It had very good power in 1st, 2nd and 3rd gears. It didn't sound completely healthy in the high RPM in 4th and 5th gear. I let off the gas for a second, and when I hit the gas again it completely shut off. After I pushed it home, I took off the cam sprocket cover (which previously everything looked healthy). The cam sprocket turns when I hit start but the cam does not. One of the holes in the sprocket appears to have flexed and I believe the lock bent out and the sprocket is spinning freely on the cam. I haven't done anything else with the quad since I have seen this. The shop guys told me the sprocket would have broke if the valve was adjusted too tight. They told me to put a new sprocket in it and readjust it again.

Any insight on this? I don't want to throw parts at a quad with a problem, but I also don't want to tear apart a top end with 155PSI for no reason. I was going to take the advice and simply order the sprocket and try again, but I just don't see why the sprocket would have broke, and am afraid something greater is the problem. I can't recheck the compression to see if the valves are burnt up w/o it... Advice? Help...

I'm going to be buying a YFZ 450 very soon or I'd just tear it apart and put a hotcam in it. I'm going to keep the bike as a spare/friend bike and want to keep it simple and cheap. It's important to me to make it as reliable as it once was.

Thanks

[OPowersports]

If the valves were tight enough to break the cam sprocket it should have never started. The only thing that would cause the cam sprocket to turn and not the cam is if the dowel pin broke or sprocket bent and was allowed to go around it. I would replace the the sprocket, dowel and bolt. Clean out the bolt hole in the cam with some brake cleaner and the new bolt, then apply blue loctite to the new bolt when installing. Check to make sure your chain is not loose, you may need a tensioner or chain. Make sure you adjust your valves with the timing marks lined up with the engine on its compression stroke ( TDC). Hope this helps!