Went out for a spin on Sunday, and what a bad one it was, on the way back home about a mile from home when the engine started rattling big time and lost a cylinder, limped home and could hear it was the left side i thought the motor was toast, only done about about 300 miles since rebuild, off with valve covers, left exhaust valve not closing hence the rattling, so off with tank, seat, panels, exhausts, brake lever, footrest and everything needed to enable motor removal, drain oil, nice and clean, Monday motor out top end off, had to cut the valve to drop it out bent both ends, guide has galled and valve obviously hung up and been hit by the inlet as it has the witness mark on it, the top was rebuilt and the valves and seats done by a very reputable engine builder, new stainless heiden valves, there was a good oil supply i always check this with open tappet covers, cam timing and tension fine, engine timing fine, carburation good, so what caused this is a mystery, only thing i can think off is valve bounce, i have a used head coming and have ordered new valves and a guide to rebuild the damaged one, any thoughts gentlemen?