Can anybody tell me what happened to my bike. I recently checked my valve clearances, all valves were in spec except for the right side intake. It was way out, I shimed it with a 220 shim to put it back in spec, put the bike back together and had three great rides. The bike never ran better. Then the fourth ride the bike ran like crap, no acceleration, tons of backfiring, and the muffler got real hot, i mean like i could feel the heat off of it while sitting on the bike. Any how, checked the valves again and the same valve was way out of speck. Started tearing the engine apart and to my dismay the crank shaft is bent, visibly bent. How did this happen? There were no pieces of metal floating around down there, I didn't drop a shim down the engine. i'm working on a total rebuild now but how on earth did this happen?