Do piston rings rotate on the piston?

[zrayr]

they rotate, but I doubt the crosshatch has anything to do with it.

Z.

[Barry_R]

Rings rotate. Factual data is a dangerous thing. When I ran Speed-Pro we had lab data that proved it. Use radioactive pellets embedded in rings to see how fast on the dyno. Turned out to be around 10-12RPM, but completely at random - sometimes they reversed themselves.

Movement was just considered to be due to variations in bore finish and profile. A poor hone job can have deep grooves in one direction and shallow ones in the other - that'll cause the rings to spin rapidly in the grooves and they will wear out very quickly. Gaps lining up is usually bad bore profile - an irregularity in cylindrical shape.

[Outwest34au]

When I ws working with red tractors umpteen years ago (spannerin') I sold a new tractor to a good OLD mate to see him out the rest of his life and make things a bit easier on him. Turned out to be the lemon of all lemons.
By 219 hours it had new injector pmp, injectors, tranny was opened up and the list went on. The engine was a Cummins 6BT and developed heaps of blowby. Wasn't going to recognised under warranty unless the blowby was measured and spec was 204-207 L/M from memory. We measured it real close to 207 Litres/ min. When the head was pulled off we saw the rings in one pot had all the groves aligned. There was a 90* section (of the 360* top view) that had no hone marks left whatsoever, in fact was a brilliant mirror finish. The other 3/4 of the bore had as new cross hatch marks still.

Proves once again that rings do rotate.
I would also say in this case that once lined up the blowby was acting as a key/ dowel to keep them aligned and they rotated as a locked set.

Finally got all his bugs sorted, and ended up working for him and did a couple of thousand hours on the same tractor, never had any issues with it again.

[olddog]

Originally Posted by Barry_R

Rings rotate. Factual data is a dangerous thing. When I ran Speed-Pro we had lab data that proved it. Use radioactive pellets embedded in rings to see how fast on the dyno. Turned out to be around 10-12RPM, but completely at random - sometimes they reversed themselves.

Movement was just considered to be due to variations in bore finish and profile. A poor hone job can have deep grooves in one direction and shallow ones in the other - that'll cause the rings to spin rapidly in the grooves and they will wear out very quickly. Gaps lining up is usually bad bore profile - an irregularity in cylindrical shape.

Was the block honed by a precision machine?

10-12rpm at what condition? WOT high rpm?

Do they rotate at idle and normal driving conditions (say 2000 rpm 30 hp)?

Does the top and 2nd ring rotate the same direction and speed, thus the gaps always stay at a fixed angle from each other?

Do the oil rings rotate?

3 piece oil ring?

[Barry_R]

[quote=olddog;1095024]Was the block honed by a precision machine?
In the Sealed Power test lab - decidedly yes.

10-12rpm at what condition? WOT high rpm?
Just "in general" - they drifted around but did rotate. I don't have access to the data anymore (corporate execution) but suspect that rotation would diminish at WOT with higher pressure loading


Do they rotate at idle and normal driving conditions (say 2000 rpm 30 hp)?
Yes


Does the top and 2nd ring rotate the same direction and speed, thus the gaps always stay at a fixed angle from each other?
No - everything is independant


Do the oil rings rotate?
Don't know. Don't think they instrumented that. Might have since.
3 piece oil ring?
Yes - SS50U

[DanEC]

[quote=Barry_R;1095025]

Originally Posted by olddog

Was the block honed by a precision machine?
In the Sealed Power test lab - decidedly yes.

10-12rpm at what condition? WOT high rpm?
Just "in general" - they drifted around but did rotate. I don't have access to the data anymore (corporate execution) but suspect that rotation would diminish at WOT with higher pressure loading


Do they rotate at idle and normal driving conditions (say 2000 rpm 30 hp)?
Yes


Does the top and 2nd ring rotate the same direction and speed, thus the gaps always stay at a fixed angle from each other?
No - everything is independant


Do the oil rings rotate?
Don't know. Don't think they instrumented that. Might have since.
3 piece oil ring?
Yes - SS50U

Very interesting - it would have been interesting to have instrumented the other rings too.

[olddog]

Thanks Barry for all this information. I find it quite interesting.

So if the rings rotate around out of phase with each other, then it should make no difference where the gaps are when you assemble the engine.

On the one that I know was assemble with all the gaps in the same spot, when pulled down (around 5000 miles), all the gaps were still lined up. Rotated the rings put it back together and the oil burning stopped. I think maybe if all the gaps get line up then the blow by and grove of oil that isn't getting wiped keeps them from rotating.

So if you start with the ring gaps staggered, and they rotate randomly, what is the statistical chance that they will at some point align on their own? I'm befuddled by that question.

[olddog]

I agree that at high cylinder pressure the compression rings are pushed hard against the piston lands, and therefore likely pinned in place from the friction. However on the intake stroke there is almost no pressure in the cylinder. So they are free to rotate during the intake stroke even at WOT. Also when the piston changes direction on the down stroke the rings are going to get pulled to the top land.

[sharkx]

So if you start with the ring gaps staggered, and they rotate randomly, what is the statistical chance that they will at some point align on their own? I'm befuddled by that question.

Conditions on initial startup after a rebuild are not normal. If the rings are lined up, due to blow by effects, there is a higher statistical probability of the rings not starting to rotate/shift randomly. Failure of the rings to move will cause excessive wear. During normal operation, there are many times when the rings happen to be lined up. You just don't want that condition the first time a new engine is started, it's asking for trouble.

If you guys are really curious and don't mind reading through a technical paper, here is a published study of piston ring rotation using an embedded gamma ray source on a piston ring.
http://article.nuclear.or.kr/jknsfil...4803285773.pdf

Bruce

[Barnsnake]

If they are rotating around randomly, it is fairly certain that they would align at some point. It is also equally certain that they would un-align immediately thereafter.

Starting with the gaps aligned at installation would likely change the randomness due to deposits or cylinder finish at the gaps.

Interesting!

[olddog]

When I was a Kid someone showed me this neat thing. Bear with me here, it goes to the ring rotation. It was a square piece of wood about 1/4 - 3/8" square and maybe 10" long. They trimmed down a pop-sickle stick to about 3", with a whole drilled dead center. Then with a sowing pin, the pop-sickle stick is mounted dead center to the end of the square stick. So now it looks like a propeller that you can spin with you finger. On one corner of the square stick notches are cut. You take a pencil and rub it on the notches, while you rub your thumb on the edge of the stick. This will cause the propeller to rotate rapidly. You move your thumb to the edge 90 deg adjacent, and the propeller will change directions. If your thumb is not on an edge the propeller will not rotate.

You can tell people any mystic bull $h1t story you want on magic or the force and they cannot figure it out. Hand it to them and they cannot make it work because they do not know where to hold their thumb.

Back to the rings rotating. Since the the cross hatch is going both directions friction is not likely what is causing the rotation. My theory is that it is vibration that causes them to rotate just like the propeller on the stick above.

[Excaliber]

I would not assume the cross hatch is perfectly equal, it's not likely to be perfect. With more or less cross hatch on either the down or up stroke and some variance between cylinders.

[CobraEd]

Originally Posted by Excaliber

I would not assume the cross hatch is perfectly equal, it's not likely to be perfect. With more or less cross hatch on either the down or up stroke and some variance between cylinders.

I thought the cross hatch was for initial break in and seating of the rings, and that it is worn off after the engine is broken in.


.

[FWB]

Originally Posted by CobraEd

I thought the cross hatch was for initial break in and seating of the rings, and that it is worn off after the engine is broken in.


.

promotes oil retention on the cylinder wall. with proper maintenance, i have seen 100k mile motors still retaining some cross hatch, when cross hatch is gone ring rotation stops\decreases

[blykins]

Originally Posted by CobraEd

I thought the cross hatch was for initial break in and seating of the rings, and that it is worn off after the engine is broken in.


.

Hone marks will stay on for a long time.....I've pulled apart engines with 100k miles on them with the crosshatch still there.

[ACademic]

Originally Posted by olddog

Since the the cross hatch is going both directions friction is not likely what is causing the rotation. My theory is that it is vibration that causes them to rotate just like the propeller on the stick above.

Originally Posted by Excaliber

I would not assume the cross hatch is perfectly equal, it's not likely to be perfect. With more or less cross hatch on either the down or up stroke and some variance between cylinders.

Great thread! You learn something new every day.

I think you both are on the right track with respect to why rotational direction and the speed of that rotation are directly correlated to the cross hatch angle and depth (and uniformity). The minute irregularities promote the motion, along with vibration and lubricity. Absent any of these variables, I believe premature failure is the result.

[twobjshelbys]

I guess I'd never thought that they didn't rotate or there would be some kind of scoring on the cylinder side from the gap (I think there was one picture of this). The cross hatch pattern will have a different effect on the ring during the up part of the stroke than the down part, so there will be some difference between the up twist and down twist.

[Sharroll Celby]

The Kirkhams need to make a Billet engine, with a sealed viewing port at the piston(s), along an accessible part of the cylinder wall. Then, with a high-speed camera, record the rings as they pass by the port, and see if the ring gaps have moved at all.

Simple, really.

[Maurice Johnson]

If they didn't rotate, 2-stroke rings wouldn't need to be pegged, huh?

[55312]

www.mugwumps.com/whammy