I went for a ride on the weekend and lost third gear. Rode home and pulled it apart and had seemingly smashed one of the circlips which aligns the third gear on the output shaft. I thought while it all disassembled would check out top end clearances. Motor has 86.5 bore (has been sleeved) of Wiseco piston type. I measured the piston and found that it was out of round in the wrong direction. (its biggest dimension was on the non thrust axis) Then i measured the piston to bore clearance and was astounded at it being 190 microns (.19mm). I have never dealt with pistons of this diameter before but i am sure this piston has collapsed. I would have thought the clearance would be about 80 microns. The fact that the rings only have .4mm gap shows that the piston has worn excessively. Could someone please advise what the proper piston-bore clearance should be and what ring end gap should be. Also are there any piston manufacturers that do o/s pistons besides Wiseco. I would prefer a cast piston as they are more rigid inherrently in design.