Re: 80HP Mercury Low Compression, Burned Piston Rings
You did not say what is the condition of the cylinder, but chances are that it needs a rebore. In that case, as jimmbo mentioned, you would need an oversize piston, and the link shows a standard size piston.
Take your block to a machine shop who does two-stroke work, and they would be able to say if the cylinder can be saved.
Peter