[SkiFly01]

Real answer would be to get a bore gauge and measure it. The piston may be reusable and even the sleeve. I have seen pretty severe detonation markings in a cylinder wall which caused no adverse affects to the engine performing, however I wouldn't run with marks like that. Your sleeve I would probably run again, but take the sleeve and piston to a machine shop and get them measured. As far as the chain, you can check how much stretch has occurred, but from first thoughts I would doubt a chain would cause cylinder wall scoring. If your timing was that far off to cause wear like that you have bigger issues. If the engine ingested debris it would cause wear on the walls and piston.