Compression ring gap question

[Kahlis]

Last night I measured the compression ring gap (top and 2nd) on all cylinders. I pushed each ring (separately) into each cylinder I planned for their corresponding piston. Once I reached about half way, I started with a .012 feeler gauge until I detected the most amount of resistance but still able to touch the cylinder wall. This is the breakdown:

Top Ring/2nd Ring
Cylinder 1 .015/.015
Cylinder 2 .014/.017
Cylinder 3 .015/.016
Cylinder 4 .014/.016
Cylinder 5 .015/.015
Cylinder 6 .015/.016

The Haynes manual states the gap should be between .00010 and .0021 (don't quote me on that - going off of memory). No discernible difference between the top and 2nd rings. Assuming these tolerances are for a stock motor, I consulted Dr. Google and his fabulous Internet Assistants. The more I researched, the more confused I got. Here are two examples:

- Superchevy.com states 2nd ring gap shouldn't be greater than the top ring unless running a HO motor, such as turbro, charged or N2O.
- Wiseco.com states 2nd ring gap should be greater to reduce top ring flutter or lifting. They even provide an example chart and formula (http://www.wiseco.com/PDFs/Manuals/RingEndGap.pdf):

2016-04-13_10-32-20.jpg

Based on this chart, using High-Performance Street/Strip as a baseline, this is what I came up with:

3.935" bore x .0045 (top ring) = .0177
3.935" bore x .0055 (2nd ring) = .0216

If the above math is correct and following Wiseco's chart, both top and 2nd rings are way off. So should a) the 2nd rings have a larger gap? - b) [if a) is true] should I grind the rings a couple thousandths so they are all even and match accordingly? - or c) really work the rings to match .017 and .21, top and second respectively?

[Russ Pottenger]

The .017 top and .021 2nd will be fine based on your chart.

The confusion is understandable.
Years ago we considered the combustion temperature and how it would affect the top ring gap.
So as one could expect, the higher the anticipated combustion temperatures would get we would compensate by increaseing the gap so the ring end gaps wouldn't butt.

While that is still true and a consideration, we are now realizing that any combustion pressure/gasses that gets passed the top ring has a tendency to want to unseat the second ring. That's the reason for the current trend is to open up the second ring gap and designing Pistons with accumulator grooves between the top and second ring package.

Hope that helped and didn't add to your confusion. .. Lol

[Kahlis]

The .017 top and .021 2nd will be fine based on your chart.

The confusion is understandable.
Years ago we considered the combustion temperature and how it would affect the top ring gap.
So as one could expect, the higher the anticipated combustion temperatures would get we would compensate by increaseing the gap so the ring end gaps wouldn't butt.

While that is still true and a consideration, we are now realizing that any combustion pressure/gasses that gets passed the top ring has a tendency to want to unseat the second ring. That's the reason for the current trend is to open up the second ring gap and designing Pistons with accumulator grooves between the top and second ring package.

Hope that helped and didn't add to your confusion. .. Lol

Nah man, that helps narrow things down. Thanks Russ.

- Lee

[Kahlis]

For sake of grinding, placing in the piston, measuring, regrinding, placing back in the cylinder, etc, etc, etc for each damn ring,...

Could I grind one top ring and one 2nd ring to .17 and .21 respectively, then measure the static distance (micrometer) and make the same for all?

Also, do you have a trick of the trade to ensure accurate cutting without potentially rounding or angling the ends?

[Russ Pottenger]

There's a specific purpose built tool for grinding and gaps on rings that I and others use.

A Stroker with the compression ratio you're running you'd be fine installing them where there at now.
If you have a plumus stone or fine jewelers file, just hit the sharp edge from the end of the ring that could transfer a scratch down the cylinder wall. Put the top and second ring 180 apart parallel to the wrist pin and call it done.

[Kahlis]

There's a specific purpose built tool for grinding and gaps on rings that I and others use.

A Stroker with the compression ratio you're running you'd be fine installing them where there at now.
If you have a plumus stone or fine jewelers file, just hit the sharp edge from the end of the ring that could transfer a scratch down the cylinder wall. Put the top and second ring 180 apart parallel to the wrist pin and call it done.

Yeah, a grinder. Been looking at videos online and pricing on eBay. What I meant was can I measure and cut just one top ring and one 2nd ring to size, then measure the space of the rings uncompressed. Record that size, then grind the other rings to match the uncompressed distance of the measured rings.

Are there benefits of increasing the gap size to .17/.21 versus keeping them as they are?

[Russ Pottenger]

Just keep the gaps where there at to keep it simple.
The relatively low static compression ratio you're running and the RPM range you'll be in will be fine.
You're not likely to experience ring flutter in your application.


It's always good to be in a habit to fitting the rings for each individual cylinder.
That said, they should all have the same finished bore diameter

[SilverXJ]

What I meant was can I measure and cut just one top ring and one 2nd ring to size, then measure the space of the rings uncompressed. Record that size, then grind the other rings to match the uncompressed distance of the measured rings.

Do not do that. Too much room for error.

[Kahlis]

Just keep the gaps where there at to keep it simple.
The relatively low static compression ratio you're running and the RPM range you'll be in will be fine.
You're not likely to experience ring flutter in your application.

What about the 2nd ring gaps that are equal to the top ring (cylinders 1 and 5)?

Top Ring/2nd Ring
Cylinder 1 .015/.015
Cylinder 2 .014/.017
Cylinder 3 .015/.016
Cylinder 4 .014/.016
Cylinder 5 .015/.015
Cylinder 6 .015/.016

Just wanna make sure I get the warm and fuzzy.

[Russ Pottenger]

Up until the last 10 to 15 years it was standard practice on high-performance Street engines to gap the top ring
.004 per inch of bore and the 2nd .003

Trust me you'll be fine where you're at.
Assembling a clean engine and a proper engine break-in procedure is way more important then an extra few thousands or so on the second ring gap.

Good Luck

[Kahlis]

Up until the last 10 to 15 years it was standard practice on high-performance Street engines to gap the top ring
.004 per inch of bore and the 2nd .003

Trust me you'll be fine where you're at.
Assembling a clean engine and a proper engine break-in procedure is way more important then an extra few thousands or so on the second ring gap.

Good Luck

Sounds good to me. Thanks again.

[jsawduste]

Confident I can speak for Dino and Russ on this one.

It sure is refreshing to see an engine get the getting the attention it needs to be called a quality build.

Suspecting that you will continue to address each aspect with the same detail as you are the ring gap.

Thank you and good job.

[Kahlis]

Confident I can speak for Dino and Russ on this one.

It sure is refreshing to see an engine get the getting the attention it needs to be called a quality build.

Suspecting that you will continue to address each aspect with the same detail as you are the ring gap.

Thank you and good job.

Thanks man, I appreciate that. This is my first true engine build, excluding the 350 I built for my '81 Z28 back in 2001 (long block arrived built, just threw Holley, Edelbrock, MSD, etc at it for a finished project).