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On 29 Jul 2003 at 22:22, Neil wrote: > I looked through my box of NOS parts and was just going to reply to Jason at > first, but then I noticed a difference. I've got several sets (ATE, Goetze, > Thompson and genuine VW). Seven sets are labeled 311 198 163 and two others > are labeled 315 198 163. According to the parts book, the 311 part is 83mm > standard, while the 315 part number is 83.5mm oversize. What's the purpose > of this? VW actually lists oversize replacement pistons and rings in their parts lists. Even though we in the west tend to think of both the pistons and cylinders as cheap replacement items, there are other parts of the world where labor is cheap and money is tight, so old cylinders would be bored out and oversized pistons installed. I believe there are 2 oversizes, in increments of 0.5mm, for every cylinder size. When I first got into this stuff, RIMCO advertized rebuilt oversize piston/cylinder sets, but I never saw one of these so I don't know whether they used VW oversized pistons or someone else's pistons. I've never seen oversized pistons advertized anywhere else, but someone on this list came up with some a few years ago. > In looking further at the Goetze boxes, one says "Volkswagen 1500 A 1,5 Ltr. > 83 X 2 + 2 + 4mm" while the other three say "Volkswagen 1500 N 1.5 Ltr. 53 X > 2.5 + 2.5 + 4mm 45 PS" What's the difference for these? Did the "A" (is > there such a thing) and the "N" use different rings for some reason? To add > to this mystery, the Thompson Products set says "VW 4Zyl. ¯ 83mm pro Zyl > 2X2.5-1X4" Compression rings have gotten skinnier over the years as manufacturers became aware of the effects of ring mass versus high rpm in an engine. The older standard was 2.5mm, but later replacment pistons came with 2mm upper rings. When you buy rings for these older sizes you have to specify which size your pistons need. By the time that VW introduced the 85.5mm (1600cc) pistons, all the rings were 2mm, so you won't find this option in this size. I'm not sure what everything in "VW 4Zyl. ¯ 83mm pro Zyl 2X2.5-1X4" means, but it looks like it has an upper ring 2mm, a 2.5mm second ring, and the oil rings are all 4m. The only thing that doesn't make sense is the -1, but maybe they're just pointing out that this is a set that has only 1 2.5mm ring per piston. -- ******************************* Jim Adney, jadney@vwtype3.org Madison, Wisconsin, USA ******************************* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ List info at http://www.vwtype3.org/list | mailto:gregm@vwtype3.org