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I read some time back on another site that it was possible to fit 1st O/S rings onto standard pistons by filing the end gap down. This can be done when the standard bore is on the limit and you don't want to risk a rebore on the pre nikasil steel lined 1000cc bores. Has anyone out there done this, and any advice on how best to do this ???thanks in advance

I did this on my 75/5. I made a jig and used my Dremel abrasive disk. It was production but kind of fun to do. I made sure to gap the rings in the cylinders of course. My result was less than great; still lacked performance so I went to a rebore and 1 over NOS Pistons after all.

Rings are manufactured to be round in the intended bore size. If you increase the gap to fit the ring into a smaller bore, then the ring is no longer round but an oval, not too good for sealing against a round cylinder bore.

George Ryals wrote:Rings are manufactured to be round in the intended bore size. If you increase the gap to fit the ring into a smaller bore, then the ring is no longer round but an oval, not too good for sealing against a round cylinder bore.

I thought it sounded hinky from the get-go. But I've never replaced rings, so what do I know?

Thanks for the feedback I'm not sure if the minute amount that will be filed off the 1st oversze rings would make them oval, but the bores are probably not 100% round anyway after all those miles....I'm trying to get around having them bored because the only machinist here in Australia that I would trust to do the re-bore is not replying to my emails ( retired, dead, in south America etc) There are no machine shops here in Tasmania I would trust, so I'll buy a ring file, borrow a hone, and have a go myself. Guess I'll find out one way or another if it works

In your situation, I think I'd do the same. It's not the "preferred" solution, but it sounds like it beats your other options.