from the looks of the top of the piston pic you posted ^^^, that is a ton of oil burnt on the valve area. when you rebuilt the top end, what kit , as in..did you use the complete kit, piston, rings, cylinder, all new ?, if you just used a new piston with new rings, and just used your old cylinder ?, then that maybe your problem. a worn connecting rod wont be good either. any time i rebuild a top end, i make sure the rings fit the cylinder, by pushing them each down into the cylinder to check for fit, if the end gap is too much ?, it will smoke !. its also very posb you bent a ring while installing the cylinder down on the piston. one thing i have learned in all my years of working on atv's and rebuilding engines ?..DO NOT RUSH THE JOB !.