Piston Ring Gaps
06-06-2005, 12:56 AM
#1
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Thread Starter
Piston Ring Gaps
Checked the ring gap on a set of Goetze rings before installing them. The 1st compression ring and the oil scrapper ring are within factory specs, but the 2nd compression rings are a little over the new spec (factory manual states 0.20-0.40mm for new with a 0.80 wear limit). I measured between 0.508 and 0.559 for the 4 new rings. The old/used 2nd comp. rings that I removed ranged from 0.533 to 0.635. Normal for the new rings to have a larger than spec gap?
Interesting is that the original 1st comp rings ranged from 0.89 to 1.19 gaps, which is well over the wear limit, but its a 50k mile engine and the leak down numbers were very good.
Interesting is that the original 1st comp rings ranged from 0.89 to 1.19 gaps, which is well over the wear limit, but its a 50k mile engine and the leak down numbers were very good.
06-06-2005, 01:36 AM
#3
Rennlist Member
The tech spec book says the gap should be .3 to .6 for the third groove, so those measurements are (just) within spec, no? Are you measuring in the bores and, if so, have you measured the bores?
06-06-2005, 12:31 PM
#4
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Thread Starter
Originally Posted by Tom M'Guinn
The tech spec book says the gap should be .3 to .6 for the third groove, so those measurements are (just) within spec, no? Are you measuring in the bores and, if so, have you measured the bores?
Michelle, what was your source/brand for your rings?
06-06-2005, 12:42 PM
#5
Nordschleife Master
My #2 compression ring was just out of spec as yours is (as was the oil scraper ring). I was told it was fine. In fact some people apparently run the #2 gap big to reduce pressure between either the #1 and #2 or #2 and #3...I forget which. I wasn't too concerned, At that point I just wanted to know that it was fine and I could continue assembly. Though I wish I remembered now...
My bores had been measured and were in spec.
I was using a goetze set of rings IIRC.
My bores had been measured and were in spec.
I was using a goetze set of rings IIRC.
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06-06-2005, 01:06 PM
#8
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Adrial, thanks, I was going to use them regardless, because they do have a slightly lower gap than the original rings, so at least they would be a slight improvement....? I was just curious if this is common or if there is something wrong with the set of rings I bought.
Michelle, did you use/get 951 part number rings or are they 944 rings?
Michelle, did you use/get 951 part number rings or are they 944 rings?
06-06-2005, 01:14 PM
#9
Jane Bond 007
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Paragon only carries one number, I believe. I talked to Jason and either someone from Lindsey or SFR, I don't remember. They said I should be okay running the 944 rings.
06-06-2005, 01:36 PM
#10
Are these the cast rings or the chomemoly rings?
06-06-2005, 01:50 PM
#11
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Thread Starter
Cast rings? I do not know, but I would be surprised to find out that any ring is made by casting. I would assume they are machined from a forging. I have no idea what alloy they are, but would guess they are a carbon steel.
The 944 rings are different than the 951 rings. The 1st compression ring for a turbo is chrome plated on the edge, the n/a ring is not. The design of the n/a 2nd comp ring (I recall) has a step in it on the cylinder contact edge, so it appears to be thinner than the turbo ring. And the oil scraper rings are different. The n/a has a 3 piece ring, while the turbo has a two piece setup.
The 944 rings are different than the 951 rings. The 1st compression ring for a turbo is chrome plated on the edge, the n/a ring is not. The design of the n/a 2nd comp ring (I recall) has a step in it on the cylinder contact edge, so it appears to be thinner than the turbo ring. And the oil scraper rings are different. The n/a has a 3 piece ring, while the turbo has a two piece setup.
06-06-2005, 02:36 PM
#12
Thanks Jim. The thing is that a boosted 928 guy had some rings shatter because he feels they were the superceded 928 rings rings which may be cast.
06-06-2005, 03:06 PM
#13
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The Goetze box that the 951 rings came in had them described as "951/928". I never checked to see what 928 uses these same rings, but thought it was interesting. Do you know which 928 engine has the 100mm pistons?
For what its worth, I was told by an engine builder that the 944 n/a rings can crack in a turbo application, and to only use the 951 chrome plated ring set. But I have also heard other sources state that the 944 n/a rings work fine in a turbo....
For what its worth, I was told by an engine builder that the 944 n/a rings can crack in a turbo application, and to only use the 951 chrome plated ring set. But I have also heard other sources state that the 944 n/a rings work fine in a turbo....
06-06-2005, 04:12 PM
#14
100mm bore = 5.0 block from 85 on up to 95.
78-84 or so is 4.5 and then 4.7.
93-95 is 5.4L with a larger stroke and same bore - but different rings because of the oil control issues on the forged GTS pistons.
78-84 or so is 4.5 and then 4.7.
93-95 is 5.4L with a larger stroke and same bore - but different rings because of the oil control issues on the forged GTS pistons.
06-06-2005, 04:16 PM
#15
That info you state Jim is coninciding with what Rob "blownbeast" on the 928 board has come up with recently. Chrome = good I think. Possible more flexible? Stable under stress? Whatever it is I will be using them on any stock 5.0 block. Do you know the part numbers?