4

So, still having problems rebuilding this old engine (Skoda Estelle 120, 70's, RWD, rear mounted engine). First of all: getting new parts is out of the question since I have no access to those. So I need to get this done with whatever (s)crap I have :) As I'm getting more into the pistons sets I have (3), I find the following problems in all of them:

Set #1: 4 pistons are good, flat tops, no dents, no scratches, slides into the cylinders correctly but the pins I have are 5mm shorter. Second problem (which I solved) is that the oil ring groove is square, and the oil rings I have (2 parts, one the ring, one a coil ring inside) won't work because these needs the oil groove have a concave inner face, to accommodate the spring ring. I fixed that by concaving it with a dremel and a ball diamond bit. So real issue is: pin is shorter. I have being told to put an extra piece in both extremes, ideally hammered down, as to correct the length, i.e, insert there 2.5mm bushes by force

Set #2: 3 pistons are good, flat tops, one had a deformity in the bottom edge by dropping, all of them slides well, rings are not a problem. Investigating that dent I see it had a very subtle small crack. Since that crack would grow with heat a pressure, using the dremel and a round stone bit I grind the deformity/crack off without reaching the reinforcement lip that can be seen in the photo. I learned about working cracks out this way but in glass, I have no idea if this would effectively stop the piston to crack. So question(s) are: would this affect the piston integrity? Looking for some balance, should I also grind the other pistons like this, controlling their weight obviously? And yes, I know this should be left smooth so it won't cut the cyls

Set #3: 3 pistons are good, dome crowns, but 1 piston is cracked at the bottom through the opening under the pin. I only could see this after I sanded them with fine grit: the dirty marked the crack. I wouldn't use that one. So I guess this set is doomed. As these are dome, and the ones in set #2 are flat I guess I can't just replace the #2's grinded off with one from this set, or viceversa, i.e, mixing the pistons (flat and dome), correct?

Overall: what's the best option I have? Would set #2 work well with that grind on the piston(s) bottom?

Set #1

Set #1

Set #2

Set #2

  • What is in the #1 set which holds the pin in place? Are there snap rings or what? I'm assuming these are not press fit? – Pᴀᴜʟsᴛᴇʀ2 May 7 '17 at 22:26
  • All the sets uses snap rings...so if left the pins 5mm shorter, it will hammer the snap rings out – Aram Alvarez May 7 '17 at 22:32
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My suggestion is to go with set #1 without any modification to the pins or adding anything to the pins. While the pins are a bit shorter than what comes stock, they should work fine. The difference of only 5mm (or 0.1969") is not a huge one. These should be handle this size of engine without giving you any problems. I think you have too many issues with the other pistons to use any of them without giving you more problems later down the road. If the #1 set is complete and the pistons are in good shape, this is definitely the route I'd go.

  • Just to add something I left: the pins are the floating kind...still no problem with that? – Aram Alvarez May 7 '17 at 22:43
  • @AramAlvarez - I wouldn't think so ... I assumed they were floating when you said they had locks. The extra room you have on the pins really isn't that much overall. I like the idea of the extra room than anything else you've presented. – Pᴀᴜʟsᴛᴇʀ2 May 8 '17 at 1:39
  • Just have a small concern about how you "dremelled" the base of the groove, this may cause cracking and separation in the future. It does depend on the thickness of the original material there and how "even" you left the resulting curve. – Solar Mike May 8 '17 at 6:59

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