ring end gaps

**tonydel** · 03-08-2011, 05:33 PM

I have a 98 z 5.7, I was looking to just freshen it up a bit. I started checking ring gaps, and I am getting .020 on my top and .019 on my second. They are seald power e-938 k rings. I also tried a set of speed pro rings. I lightly honed the cylinders just enough to break the glaze and cross hatch. All the cylinders are within spec? When I check with the original used rings they are much larger. I had no ridge when I took it apart. The gm book calls for .0090-.01496 top and .00173-.00251 on the second. The specs I am reading seem really tight? I am considering a set of file to fit, but this makes no sense to me? would greatly appreciate some advise.
Thanks
tony

**bills98ta** · 03-08-2011, 05:43 PM

I think I took mine to .026 for nitrous... Extra heat will cause them to expand and close the gap.

**tonydel** · 03-08-2011, 06:05 PM

I really dont intend to do nitrous, Just some ported heads and a small cam. I am jus concerned at this point with these gaps. Car did not burn any oil before. I just felt it was time to freshen it up, as long as i was doing heads and a cam.

**blackmagicturbo** · 03-08-2011, 10:09 PM

Since your cylinder is loose from mileage its probably gonna be a bigger gap to start with ,, i would go 20 top ring and 22 second ring if your gonna stay n/a ,, itll be fine ..

**Firebirdjones** · 03-09-2011, 06:52 AM

Ring gaps all vary due to many things.

The type of piston used.....Hyperutectic pistons require larger top ring gaps because of the pistons unusual expansion rate.
Then their are questions like, Pump gas, nitrous, or some other form of power adder, street/strip, bracket racer etc....

It really gets into a science as to larger top ring gap and tighter second ring gap,,,,or some builders say vice versa to allow gasses to escape and avoid ring flutter. Some pistons have gas ports for this, and it just goes on and on.....

To keep it simple, a good baseline for ring gaps are .004" for every inch of bore you have.

For example. 4" bore x .004" = .016" ring gap. Then work from there. I prefer file fit rings, and then follow the piston manufacture specs as every piston has their own ring gaps the manufacture prefers.

**tonydel** · 03-09-2011, 01:34 PM

I guess my question is will this cause any problems if I install them with gaps this wide. Will it consume oil? Or cause other problems. Could I have removed that much material honing with a cordless drill on slow speed using a 3 stone hone and motor oil? Is there any chance the gm service manual is wrong? .00251 sure seems tight on a second ring gap?
Thanks again
Tony

**bills98ta** · 03-09-2011, 01:53 PM

http://cgi.ebay.com/ebaymotors/New-P...item27b95d6bee

**Firebirdjones** · 03-09-2011, 03:03 PM

Originally Posted by tonydel

I guess my question is will this cause any problems if I install them with gaps this wide. Will it consume oil? Or cause other problems. Could I have removed that much material honing with a cordless drill on slow speed using a 3 stone hone and motor oil? Is there any chance the gm service manual is wrong? .00251 sure seems tight on a second ring gap?
Thanks again
Tony

Are you reusing the stock pistons??

If so, I'd stick with the stock gaps that GM calls for if this is a naturally aspirated engine.

If it is in fact what you posted, then it appears your second ring gap of .019 falls right into GM spec of .017-.025

Your top gap of .020 is on the large side, especially if GM is calling for .009-.014
.009 sounds pretty tight to me, but if that's what the book says

A too large of a gap does cause some issues, you'll have more blowby so it causes excessive crank case pressures, that lost compression is lost performance. Sounds like you may need file-to-fit rings and adjust them accordingly.

**blackmagicturbo** · 03-09-2011, 06:18 PM

Originally Posted by Firebirdjones

Are you reusing the stock pistons??

If so, I'd stick with the stock gaps that GM calls for if this is a naturally aspirated engine.

If it is in fact what you posted, then it appears your second ring gap of .019 falls right into GM spec of .017-.025

Your top gap of .020 is on the large side, especially if GM is calling for .009-.014
.009 sounds pretty tight to me, but if that's what the book says

A too large of a gap does cause some issues, you'll have more blowby so it causes excessive crank case pressures, that lost compression is lost performance. Sounds like you may need file-to-fit rings and adjust them accordingly.

He already said his stock ring gap was bigger than .020 so if it wasnt using oil before why would it with a .020 gap top and a .022 second just saying ,and it leaves him room for a small shot later on.., because nobodys happy with stock motors ,,even h/c combos..

**Firebirdjones** · 03-10-2011, 07:04 AM

Originally Posted by blackmagicturbo

He already said his stock ring gap was bigger than .020 so if it wasnt using oil before why would it with a .020 gap top and a .022 second just saying ,and it leaves him room for a small shot later on.., because nobodys happy with stock motors ,,even h/c combos..

He said his stock gap on the top ring is .020 after he honed it is what I understand. I highly doubt the stock gap on a virgin engine was that large unless it had bookooo miles on it. He states GM recommends .009 - .014 on the top ring. If that's how they are built when new,,,then .020 is way out of spec. Best to get a file fit set and make it right. This isn't something that is easily corrected after the fact. Do it correctly now or don't do it at all. You don't tear them down this far to half ass it now. Just my opinion from working in and around machine shops. Those guys would never let something go out the door like that. Bad for business.

And who says no body is happy with stock motors, or head/cam combos?? How much power is enough?? You can build 700 hp naturally aspirated motors if you know what you are doing. Not everyone has to have a power adder

**tonydel** · 03-10-2011, 05:09 PM

The gm book calls for .0090-.01496 top and .00173-.00251 on the second. I don't think I can be comfortable with these numbers? 2 1/2 thou on the second seems rediculous? I wish I had a way to find out if GM made a mistake in the book? Do you guys running 20 and 22 consume an oil?

**Firebirdjones** · 03-10-2011, 06:31 PM

Well the second ring gap doesn't sound bad, that's fairly normal with most ring packs. The second ring gap is always larger than the top ring on stock type stuff. It's when you get into custom piston designs and different ring packages where engine builders will change things like tightening the second ring and actually running a larger top ring gap. There are alot of different theories on that. Some believe this helps gasses escape and promotes better ring seal, while others feel the opposite is true.

Your best bet,,,and it's what I always do when building an engine, is to follow what the piston manufacture recomends for ring gaps. It's always in the paperwork. Different manufactures make their pistons from various materials, and they all have different expansion rates that affect piston ring gaps.

For instance, the hyperutectic pistons in a 406 I built came with a chart to follow for the top ring gap depending on the intended use of the engine.
Even a naturally aspirated pump gas mild street/strip engine wanted a rather large .020 or .022 top ring gap (don't remember exactly now)
But it was due to the piston material and it's ability to absorb heat and expand, which closes the top ring gap. Theoretically by piston design it should close the gap by at least half that amount once the engine is warm. But you start with that large of a gap on these pistons to avoid the top ring from butting together. In which bad things happen like broken piston ring lands and scarred cylinder walls or worse.
This particular engine only has a cold cranking compression of 140. When the engine is hot however it holds 185-190. It has no oil consumption issues. But as I mentioned, by design the larger top ring gap tightens up when warm.
Other pistons don't expand that much and require much tighter gaps to start with.

I don't have my GM book handy so I'm not sure what they call for on gaps other than what you are posting here, assuming the stock pistons are being used.