Is the cylinder liner scored or does it have delaminated aluminum from the piston adhered to it? If the vertical lines will hone out, that's ok. If honing does not remove the scratch and you overhaul it, it will run ok for a while. All the time exhaust gas will migrate down that scratch towards the piston rings. Over time the ringset will carbon up and it's likely you may have another premature failure. Best to overbore just that one cyl. That is an acceptable factory repair. Make sure you get a factory replacement oversize if the other 5 are all stock factory pistons. Bombardier makes them in .020, .030 and .040 oversize. If you have piston aluminum adhered to the cast iron cyl wall, you can remove it carefully with some muratic acid, then hone it, replace that one piston only. I'd put 6 new ringsets in the engine during overhaul. You'll want to know the reason for the failure prior to re-starting the rebuilt engine. I'd be looking at the carbs-to see if the main jets may be restricted on the low compression cyls. Also possible those cyls were overheating, so check the rubber water diverters by each cyl to be sure they are correctly installed. Those were sought after engines in their day. Put out close to 165 hp at the prop.
