Have dismantled my top-end, bottom end and have got the case apart - running a #3 Puch Maxi Alu-series cylinder/piston, post-seize.
Cylinder wall looks shiny, clean, smooth - no obvious gouges/streaks....piston looks smooth and clean....but doesn't fit properly in the cylinder. Gets about halfway down then snags. Clearance is about 0.04mm but I think the problem is the piston skirt is too wide, since putting the piston in from the top, crown first, is okay until the piston skirt gets into the cylinder.
Any cure for this, or is it new piston/cylinder time?