Earlier 7-10 models like mine had thick rings (63290/87166), but looking through the IPL's I see some later models did have thin rings (89732). To confuse the issue, if you look at the McCulloch cylinder/piston charts you will find the same piston (85239) described using the thick rings (87166) and the thin rings (89732). I think in fact the piston used with the thick rings was 69030 or 85240 but they weren't very careful when they were printing the piston/cylinder lists. You won't find 69030 in any piston/cylinder list but it appears in the IPL's.
Unfortunately is was common for these saws to be run too lean and scored, the SP70 and PM700 were more likely to be scored than the 7-10 in my limited experience. Those both happen to be chrome bore models and I have 3 or 3 PM700 saws and a couple of SP70's in the attic that suffered such a fate.
The early 7-10 saws had a cast iron bore and seemed to be less prone to scoring problems.
A long while back Steve AKA 6-10 asked about the 6-10 vs 7-10 pistons so I took some photos. The piston on the left is from a later model 7-10 with the thin rings PN 85239, the piston on the right is from an early 7-10 or 6-10, PN 85240.
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Mark