No problem, clean up the cylinder & head and add a new piston then go for a ride. New piston survived initial startup and not much more. Seems it caught a ring on a bit of undetected debris . I blew out the crankcase and ran a magnet thru it, but I did not bother to thoroughly rinse it out w/ gas. So 40 euro later for a 3rd piston plus a 10 euro pro hone and the problem is solved. We inverted the motor and carefully flushed every nook & cranny in the crankcase w/ a ~1/4" tube inserted until the gas came out clean, then blew it out w/ air. Listened for any crunchiness in the bearings and heard/felt nothing. The motor now runs great and w/ a fresh DR90 kit you know it will be powerful .
we reinstalled the motor with the frame still upsidedown - SO easy!
Last edited by V oodoo on Sun Mar 01, 2020 12:40 am; edited 1 time in total