It sounds like it's catching on something like the exhaust port. When you redid the top end, you changed rings and all, right? Your exhaust valve may be slipping deeper into the cyclinder head so check that as well. That's usually the only moving part that comes near it. If you have too much play in the piston it'll move around in the port as well. You should be able to see what side chipped off, then go from there. Look at your port openings and make sure there's nothing stuck in there. If you had it resleeved it should be back to specs but I believe you can't run both types of pistons anymore. FWIW, in the future, you can have your cyclinder worked back up and replated, that way it stays stock instead of the sleeving. It may cost a bit more, not by much but you can then run both types of pistons.