Ring end gap

[78Chev]

I'm rebuilding my red block 6.2. Had a machine shop bore it out by measuring my Mahle .040 pistons. I had them do 1-6 with .004 clearance; 7-8: with .0045 clearance. I did not see the measurements afterward so I'm trusting their work at this point, but they are a reputable shop.

I bought a set of .040 or 1 mm oversize rings made by Sealed Power.

Tonight I measured the end gaps of the top rings and found that they were from .016 to .021 (spec = .012 to .022) so they were high but in spec. The bottom compression rings ranged from .040 to .049 (spec = .030 to .040 according to Haynes) so they were way over spec.

Any thoughts on what I should do?
Thanks - Randy

[john8662]

Hmm, ran into this with my 6.2 rebuild too.

Both my upper and lower compression rings ended up having more gap than what the book called for, but not much. I can't recall what my gap for the 2nd ring was now (shoulda wrote it down I guess).

Anyways, I did find that different ring brands did vary a little (usually only .002" though).

The bore clearance you specified is right where you want to be.

Have you physically measured the piston and then measured your bore diameter to check your machine shop?

I think you'll find that they did a good job and that the piston is actually a little larger than a .040". At least, that's what I'm thinking on mine, the rings had the larger gap, but the bore size was right, so the rings are based on a calculated .040 verses measuring the piston and boring the holes to match the size of the pistons. The right way is what you've had done, measuring the piston and boring.

Might try another set, even though that's money wasted.

I found the Mahle brand rings were a little tighter, not much...

[78Chev]

Thanks John.
So what did you end up doing? Did you just live with bigger gaps?

What about going to gapless second rings like Ronnie Joe did?

[john8662]

In the end I just lived with it. I called my local machine shop and spoke to the fella that puts the engines together after the machining, he say's it's becomming more common to see larger gaps.

I noticed more blow-by than I wanted at first, but now it's almost none, I guess it's more of a break-in thing.

Hastings makes two ring sets for the 6.2, one that's supposed to use close to factory specs, and another that has the 2nd compression ring with a smaller gap. This actually might solve your problem in this situation. The only thing I didn't like about the Hastings rings was the oil control rings they used on the 3rd piston groove. I prefer the 2 piece oil control ring type, the other is a three-piece (looks like what SBC gassers use).

In a recent tear-down of a core engine I received, it had been rebuilt, and had the 3 piece oil control rings, they were ALL stuck, I suspect the engine used more oil than it should. That sold me on the 2 piece design.

What did the Sealed Power setup have?

J

[grape]

usually ring gaps are recomended by the ring manufacturer for different types of applications, ie. turbo, nitrous or N/A use. Usually the gap measurement is .004" per inch of bore, some severe use stuff is up around .005" per inch of bore.

[78Chev]

The oil rings in the Sealed Power set are 2 piece. I noticed in the Total Seal catalog that the oil rings for gapless were 3 piece. I too like the 2 piece oil ring so I'm still trying to figure out what to do. Some of my 2nd ring gaps are almost 25% larger than max spec (.049 vs .040) which seems like a lot to me.

[john8662]

I don't see any harm in using another ring set, but keeping your 2 piece oil control rings rather than what came with another set.

I agree the .049" is a bit large, I'm curious what you'll find.

Perhaps a re-mic of the cylinder bores and piston skirts (~1" from the bottom of the skirt) just to make sure that the bore is correct. It may very well be the rings themselves, that's why I recommend another set. I ended up doing the same too.

[78Chev]

I will re-mic everything. Since the top rings are in spec but the bottom ones aren't I suspect it is the rings. I'll give the guys where I bought them a call and see what they say.
Randy

[Robyn]

I just rebuilt my 6.5 TD and I had to file the second groove ring as they were way tight. go figure?????????????

[john8662]

I just rebuilt my 6.5 TD and I had to file the second groove ring as they were way tight. go figure?????????????

STD bore they seem to be getting right, because of the better quality control that GM's piston supplier used during piston casting. So a ring contructed for this size usually came out correct, because of the "calculated size"

The aftermarket pistons on the other hand may or may not be the right size specification, all goes back to what the STD size is plus the oversize. There is some discrepency between what the stock bore size was, well, according to some...

I agree, I just assembled a stock bore 6.5 with new Mahle rings, and had great ring gaps, didn't have to file anything...

Robyn, what ring brand did you use?

I've only dealt with Mahle and Hastings thus far..

[78Chev]

So I ordered a set of gapless second rings from Total Seal. They were very helpful and said it is fine to run their gapless rings with my Sealed Power top and oil rings. The gaps for these rings are supposed to be about .019, which is about the same as the top conventional rings I have. We'll see how this little experiment goes...
Randy

[john8662]

Check out RJ's articles, one of which covers the Total-Seal Gapless rings and the little issue that his rings had in regard to being true. Just to know what to watch out for. Since these rings you're getting are probably from scratch, you won't have that problem, but something to watch for.

I'm still trying to figure out why I hear so many fellas that say that using gapless rings "eat the hell out of the cylinder walls" I'm not so sure that's true if everything is correct of course.

J

[78Chev]

As I understand it, RJ had Total Seal machine his original rings into gapless rings. When he broke one trying to straighten it out TS sent him a new 2nd ring set which was gapless from the beginning. So hopefully since mine are made gapless from the get go I shouldn't have the twisting problem - but we'll see.

Hopefully the rumors of gapless rings eating cylinder walls are not true - or at least any worse than other rings. I guess I'll find out. Also, TS has a special ring seating compound that is supposed to work great.
Randy

[john8662]

I wouldn't think any ring seating compound would help in a diesel engine. The high compression does a pretty good job of seating the rings...

Worth a try, but as you've discovered the key is good ring gap!