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If you can take the cylinder to a proper machinist and have him measure the bore in several places as well as the piston, it would give you an idea if it needs to be bored out or just honed with new rings.
Thanks, I'll do that tomorrow. Having no Vespa guys anywhere nearby, it will be a normal engineering/machinist shop. So they wouldn't be able to advise me on stock sizes and oversize numbers.
Which wear away quickest: the actual rings or the cylinder (grinding away at the bore)? In other words: can the rings wear to such an extent that it is smaller than originally or would it rather eat away at the cylinder? The two different size gaps (edited in OP - .86mm and .73) make me think the rings wear easier?
The top part of the cylinder, where the discoloring start (probably about 8mm), where the piston stops, doesn't have a large lip (lack of better word?). When measuring the rings in that area give both rings a 0.03mm smaller gap, so essentially 0.03mm of the original bore has been worn away....correct? Not much, so I would think only rings would be in order?