On my 1999 Sportsman 500 the exhaust lobe on the cam was worn down completely. I replaced the cam and rockers. Set timing correctly. Set valve clearance to .006 at TDC. Fired it up and it ran beautifully for 20 seconds. I gave it throttle and once I got to half throttle... "Snap!" Motor died and the timing chain had broken. I guess my question is: What would have caused the chain to snap? Will the valves be ok if I were to just replace the chain and reset timing?