Goetze Ring End Gap too big - 1980 3.0 SC

[spunky.goat]

I’m rebuilding my 1980 SC 3.0L w/ the stock Mahle cylinders and pistons. I measured the cylinders and they are all in spec. The new Goetze ring (p/n 08-320900-10) Compression 1 and 2 rings where above ring end gap specification.

I measured the ring end gap w/ the ring inside the cylinder located in the same plane as the base gasket and used a depth gage to ensure the ring was located at a consistent location around the circumference.

The spec range for ring gap is 0.15-0.30mm, I measured 0.4mm on one ring and 0.5mm on another ring. Out of curiosity , I measured my old compression rings and they measured at 0.56mm.

I’m thinking this is not OK and that I need to locate a different set of rings that meet spec.

Have others experienced this with Goetze rings? Are there other brands recommended that will meet the end gap spec?

Or is the larger ring gap OK?

[Alan L]

This seems to be a commonly reported problem. Why they don't provide them under size and allow you to gap them according beats me.
Alan

[Zuffenwerker]

Spunky-goat!

This is normal. Why it’s normal idk but I see it all the time no matter the ring manufacturer..goetze, mahle, je, etc. My best guess is they don’t care about the Porsche spec you find in the literature. The modern piston ring industry revolves around .0045” end gap per inch of bore diameter for the top ring give or take and slightly more for the 2nd ring. That means for your sc they think the top ring gap ought to be .42mm and your 2nd ring gap .47mm.

Take a look at the wear limit Porsche lists for ring gap as I recall it’s huge. You are good to use them as long as they aren’t too tight

[Alan L]

Yes - I was given 0.004" per inch of bore by a good engine builder when I was building a race engine. Luckily the rings provided allowed me to gap them to this and a bit less.
But this seems a common number. There is probably not much you can do about it.
From memory last time I fitted new rings to a 911/930, the gaps were just on the factory limit, brand new. Disappointing, but probably not of great consequence on a street motor.
Alan

[Alan L]

So here would be my take on it - from a manufacturer point of view. What tolerance can they make them to at a competitive cost? +/- 1.5 thou? So they aim for the minimum clearance by Porsche specs. Then some rings are marginally too tight. Warranty claims? How many people possess a ring gap grinder?
Better to make them consistently slightly large?
For race engines there are gapless rings, but for street engines, is it really an issue - considering most people with a new built engine will have no idea what the ring gap is.
Alan

[safe]

Personally I think the ring gap wear specs given is an indication of the rings being worn not necessarily that the gap it self is too large.
For a turbo or nitrous engine you set a much larger ring gap to cope with the extra heat. But they don't run on high boost/heat all the time, 90% of the time (off power adder) they run fine with a larger gap. Even if you have a large gap of 0.5mm (cold that is), its still a quite tiny hole.
Doing a leakdown you can measure a bigger leak with a larger gap but that is low pressure and low flow.
Trying to push gasses thru at super sonic speeds the flow will probably stall and you can't get much gas to pass.

That's my amateur take on it...

[Zuffenwerker]

Originally Posted by safe

Personally I think the ring gap wear specs given is an indication of the rings being worn not necessarily that the gap it self is too large.
For a turbo or nitrous engine you set a much larger ring gap to cope with the extra heat. But they don't run on high boost/heat all the time, 90% of the time (off power adder) they run fine with a larger gap. Even if you have a large gap of 0.5mm (cold that is), its still a quite tiny hole.
Doing a leakdown you can measure a bigger leak with a larger gap but that is low pressure and low flow.
Trying to push gasses thru at super sonic speeds the flow will probably stall and you can't get much gas to pass.

That's my amateur take on it...

I agree with you once you reach the end gap wear limit your rings are wore slam out if they started life in the new installation range. A little bigger is not a bad thing, the bigger the ring gap the better the ring seal. the compromise is blowby but as the man above pointed out it’s really not a worry. I recently installed some mahle Motorsport 2.4 p&c with a huge 2nd ring gap, double the Porsche spec. I called and they said it’s by design for increases ring seal.

[spunky.goat]

Thanks all for the feedback. I posed this question as this is my first engine build and trying to adhere to Porsche specs, but I don't have the knowledge of where/when it is acceptable to deviate from the specs.

Since the original post, I contacted Geoetze technical support and a product manager there indicated that gaps up to 0.5mm are OK and that my rings were manufactured within their specs (although he would not share their tolerances).

I think I will proceed with the Goetze rings. Thanks much for the quick feedback!

[PeteKz]

Getting on this thread late, but a few more things to consider: I'll guess that Goetze (and others) are just using the wider ring gap spec for both rings. That way they don't need two different processes to make rings. I can't see that 0.1mm more would make any difference in a street engine operation. The most important thing is that they are not tight. As Zuffenworker mentioned, the max wear spec is large. If the gap for one ring is slightly larger than the other, use that in the #2 position.

And another thing for you gurus, why is the #2 gap bigger than the #1 gap? To a Mech E, this seems backwards. The #1 ring is closer to the combustion chamber and gasses, so it should get hotter and expand more, thus need the wider end gap. Some years ago, when I built a Ford 351 engine, I recall(perhaps incorrectly) that the #1 ring gap was larger than the #2. I also recall that race engine builders use larger end gaps because those engines run hotter, so the rings expand more and need more space to grow.

[Mr Beau]

Second ring gap is larger to ensure no gasses get trapped so first ring can do it's job better.

[PeteKz]

Originally Posted by Mr Beau

Second ring gap is larger to ensure no gasses get trapped so first ring can do it's job better.

Thanks.