Piston rings are a very crucial part of a two stroke engine. If the rings stick they can be freed up, assuming there was no cylinder damage involved. If the cylinder is smeared vertically with aluminum it is damaged. The cylinder will need to be cleaned up with muriatic acid then honed out until the lines are gone. If too much honing is required the piston may not be large enough anymore and may need to be replaced. If the rings are only stuck then they need to be removed. If they are stuck hard you can try to soak the piston in diesel fuel or pb blaster. The ring may need to be pryed out carefully.

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When the ring is out you can use high numbered fine sandpaper to sand the wide part of the ring. Do not sand the inner or outer part of the ring. It is a good idea to take the 600+ grit sandpaper and set it down on something very flat. Spray the sandpaper with wd-40 to help the sanding process. Lay the ring down on the sandpaper and swirl it around on the sandpaper if the ring has irregular wear or carbon built up on it. Carefully use a thick razor blade or something that will easily fit into the ring land of the piston.

Pass the wider back side of the razor blade around the piston ring land and clean up any deposits that would stop the ring from moving freely in the ring land. Reinstall the ring and move it to make sure that it moves freely in the amount of space that it has.