Joe,
I agree with Jonathan that the gudgeon pin has moved and scored the bore.
You have 2 choices.
1. Replace the barrel and maybe the piston depending on size and condition.
2. Rebore oversize if you can locate a suitable piston.
I have new oversize gudgeon pins and the pads unless you have the later piston that was fitted with circlips.
Neil
Joe,
There is a brand new 60 thou oversize piston on ebay which is a really good price and may resolve the problem.
Nothing to do with me as it is in the Netherlands.
Neil