Ad0911

I am in serious doubt whether or not I should change the 3rd piston rings. The first (top) and second ring have reached the outer limit of the tolerances. The third ring (the oil scraper?) has a tight 0,1 mm groove clearance. I haven't measured the ring gap because I left the ring on the piston. By the looks of it, it seems in much better shape than other bottom rings I have seen on other engines. And I must admit that I prefer the design of the old one to the new one because of the overlap of the top end of the ring and bottom of the ring. The new one has a straight gap. Seems to me a typical case of "don't fix what isn't broken" but at the same time it seems like I did a poor job by not replacing the bottom ring while I was in there. Opinions?

I must admit that I am just a little scared of taking the old bottom ring off and putting a new one on because I have experienced braking one many years ago on a VW beetle engine

davek9

I have nothing to add to your question, as its all new if out of spec. or bad testing results.

However what was the reason you are re ringing the engine, they usually don't need it.

What was the Comp and Leak down test results?

GregBBRD

Replace all the rings with the new rings.

The original oil control rings were 3 piece with stainless scrapers at the top and bottom. You can see corrosion/damage on the edge of the scrapers in your picture (or what appears to be corrosion in the picture.)

The newer design oil control ring is a better design.

Yes, you can break the new rings if you force them apart too far in order to get them over the piston, but this takes a fairly "ham fisted" person to do this.

Buy a ring installation tool to expand the new rings when installing.

chaosmm

Hey guys,

i registered myself, because I own a "problematic" 928 here in germany Thanks for letting me in and join your community.

Yes, this threat is nearly 6 years old, but very interesting to me right now.
I opened up a spare engine (M28.01 - ATR) to rebuild it. Know I noticed, that the bore is already 95,5mm and the diameter of the crank for the piston rods meassures 51,45mm.

Now, the problem is, that the "old" ring version -shown in the pics above- are mounted, but not available in 95,5mm anymore, just 96mm. But the bore is nearly perfect.
Can I replace them for sure with the newer version or are there any details in the pistons itself, which makes it not fitting?

In all the Porsche-catalogues they talk about -79 and 80- for pistons and rings.

Sadly, this threat ended with no feedback, that it worked, so I´m asking.

Thank you for your answers, Marius

GregBBRD

If you can't buy rings for 95.5mm, you will need to re-use the rings you have.
96mm will not work, properly.

chaosmm

now that was a missunderstanding.
the newer version of the rings is available in 95,5, looks like on the picture above (one part 3.Ring with a spring) .

But mounted is the older version (two thin layers with the wobbly thing inside). And this isn t available in 95,5 anymore.

Can I replace the old version in 95,5 with the new version in 95,5 (because these are available)?

​​​​porsche sais: Old -79, New 80-

GregBBRD

Yes.