The Science of the Second Ring

Lineslinger · Mar 16, 2019

For those interested, not sure if this right forum but figured it a good launch point.
Here is a good article offering some real insight into modern day piston ring science, and why compression technology continues to progress.

https://www.lsxmag.com/tech-stories...d-ring-the-science-of-the-second-piston-ring/

Pete Komarek · Mar 16, 2019

Interesting article. Something I've wondered about. Thanks!

acotrel · Mar 16, 2019

As I understand it, ring flutter occurs at piston speeds near 5000 feet per second and the pistons in Norton Commandos approach that speed, because of the long stroke.

http://korihandbook.federalmogul.com/en/section_39.htm

jseng1 · Mar 16, 2019

See this article for a more comprehensive view:
https://www.motorstate.com/TheGreatPistonRingControversy.htm

"Piston manufacturers, including Ross, Wiseco and JE, reduce inter-ring pressure and ring flutter by machining pressure balance or "accumulator" grooves between the top and second ring lands to increase the effective area between the top and second ring. "All of these ideas may exist in a given application", according to J.E.'s Randy Gillis, "but even with all of the engine variables, ring flutter should be a concern only in excess of 8,000 RPM." Gillis doesn't see the advantage to widening the second ring gap over traditional recommendations. Brian Nutter of Wiseco doesn't feel that flutter is much of an issue until the engine reaches 8500 RPM. "The second ring runs at much lower temperatures than the top ring," said Nutter, "and requires no additional end gap clearance."

It just depends on who you listen to.

Triton Thrasher · Mar 16, 2019

jseng1 said:
See this article for a more comprehensive view:

But a view from 18 years ago.

according to J.E.'s Randy Gillis, "but even with all of the engine variables, ring flutter should be a concern only in excess of 8,000 RPM."

Is he talking about long-stroke engines? Someone mentioned mean piston speed earlier.

Gillis doesn't see the advantage to widening the second ring gap over traditional recommendations.

He may not “see” it but has he tested it?

"The second ring runs at much lower temperatures than the top ring," said Nutter, "and requires no additional end gap clearance."

Sounds like he’s answering a different question, about heat expansion.

Dances with Shrapnel · Mar 16, 2019

jseng1 said:
See this article for a more comprehensive view:
https://www.motorstate.com/TheGreatPistonRingControversy.htm

"Piston manufacturers, including Ross, Wiseco and JE, reduce inter-ring pressure and ring flutter by machining pressure balance or "accumulator" grooves between the top and second ring lands to increase the effective area between the top and second ring. "All of these ideas may exist in a given application", according to J.E.'s Randy Gillis, "but even with all of the engine variables, ring flutter should be a concern only in excess of 8,000 RPM." Gillis doesn't see the advantage to widening the second ring gap over traditional recommendations. Brian Nutter of Wiseco doesn't feel that flutter is much of an issue until the engine reaches 8500 RPM. "The second ring runs at much lower temperatures than the top ring," said Nutter, "and requires no additional end gap clearance."

It just depends on who you listen to.

Can't tie it to RPM unless you are talking about a specific engine with a specific stroke. It's tied to mean piston speed. Were they referring to 89mm stroke Nortons

jseng1 · Mar 16, 2019

There are different opinions on ring flutter and ring gaps. It depends on who's talking. I've talked to piston/ring manufacture reps about this and heard opposite opinions from people within the same company.

Who has ever tested and demonstrated a ring flutter problem with Nortons?

I've run the wide gap on the 2nd ring (as supplied by JE at .020+") and I've run gapless 2nd rings. From what I see - with the gapless 2nd ring your oil stays cleaner than with the wide gap (less combustion chamber carbon finding its way to the sump). It also revs beyond 8000RPM no problem with the gapless rings.

I'll take the cleaner oil (and a longer lasting motor).

Triton Thrasher · Mar 16, 2019

jseng1 said:
Who has ever tested and demonstrated a ring flutter problem with Nortons?

Leo Kuzmicki?

jseng1 · Mar 16, 2019

What does Leo Kuzmicki have to say about Ring flutter on a Norton twin and what Norton piston speed & 89mm stroke RPM are we talking about?

Triton Thrasher · Mar 16, 2019

jseng1 said:
What does Leo Kuzmicki have to say about Ring flutter on a Norton twin

You didn’t ask about twins, but anyway I’d be the last to know.

and what Norton piston speed & 89mm stroke RPM are we talking about?

The ones that correspond with excessive mean piston speed and cause ring flutter, obviously.

jseng1 · Mar 16, 2019

When you talk about excessive piston speed on a 89mm stroke Norton you are probably also talking about severe piston & bore wear and other problems such as broken cranks and cases that make ring flutter a moot point.

MexicoMike · Mar 16, 2019

As stated, there is a variety of opinion from major manufacturers and engine builders. A few years ago one of the prominent builders advocated running a smaller gap on the 2nd ring than on the top ring. I seem to recall that at least one ring manufacturer recommended the same. It's like the controversy about lubricating rings when installing in the cylinder. The recommendations from "experts" include: "Use engine oil," "Use WD 40," "Install dry."

What to do, what to do...

acadian · Mar 16, 2019

I just went with the .004 x " ratio for the top ring, and .0035 x " for the second ring on my new engine, that gave me .011 and .010 respectively on a +.020 bore. A very light pinch of oil on the rings, and Total Seal's "Quick Seat" in the bores. The pistons have been ceramic and friction coated, so I probably could have tightened them up a bit...

jseng1 · Mar 17, 2019

When I was racing there was talk about tightening up the top ring gap and claims of positive results. I called a ring company and was told by an "expert" that .008" was too small and that it would lead to damage. I raced it at .008" and never had a problem. I set up my cafe Norton with .008" top ring gaps during my last rebuild and that was 45,000 miles ago. It also has gapless 2nd rings.

See the leak down test at 40,000 miles.

When I rebuilt my small block Ford the end gaps seemed too large at around .028". I called Hastings rings and was told that they were within spec and was quoted a bunch of numbers "blah blah blah". After the new build it started smoking immediately. I was pissed so I special ordered custom rings from Deves that had a tighter end gap. I had to rebuild the motor all over again - but it stopped smoking and hasn't smoked since.

Sometimes you just have to find out what's real on your own.

acotrel · Mar 17, 2019

jseng1 said:
When you talk about excessive piston speed on a 89mm stroke Norton you are probably also talking about severe piston & bore wear and other problems such as broken cranks and cases that make ring flutter a moot point.

How would you know if you had ring flutter when you are using a motor in a way which maximises the use of it's great torque characteristics ? - Would a dyno tell you ?

Lineslinger · Mar 17, 2019

jseng1 said:
When I was racing there was talk about tightening up the top ring gap and claims of positive results. I called a ring company and was told by an "expert" that .008" was too small and that it would lead to damage. I raced it at .008" and never had a problem. I set up my cafe Norton with .008" top ring gaps during my last rebuild and that was 45,000 miles ago. It also has gapless 2nd rings.

See the leak down test at 40,000 miles.

When I rebuilt my small block Ford the end gaps seemed too large at around .028". I called Hastings rings and was told that they were within spec and was quoted a bunch of numbers "blah blah blah". After the new build it started smoking immediately. I was pissed so I special ordered custom rings from Deves that had a tighter end gap. I had to rebuild the motor all over again - but it stopped smoking and hasn't smoked since.

Sometimes you just have to find out what's real on your own.

You had to pull it and start over?!
Whoa... I bet I could have learned some new words in your shop.

acotrel · Mar 17, 2019

I always thought the pistons were moving too fast for the ring gaps to cause much loss of compression. I always stagger the gaps as I assemble the motor. But this pressure thing between the two rings has got me thinking. With my motor and the close box, I have trouble stopping it from over revving, even though I run very high overall gearing. If I am not careful, it will go straight through the top.

acotrel · Mar 17, 2019

Lineslinger said:
You had to pull it and start over?!
Whoa... I bet I could have learned some new words in your shop.

I would have just used thicker oil.

jseng1 · Mar 18, 2019

Lineslinger said:
You had to pull it and start over?!
Whoa... I bet I could have learned some new words in your shop.

As they say - "I exhausted my vocabulary"

Danno · Mar 20, 2019

I've often wondered why more gapless (Dykes?) piston rings are not in common use. The advantages seem obvious. What are the disadvantages other than increased cost?

The Science of the Second Ring

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