Do piston rings rotate on the piston?

[mr bruce]

http://www.totalseal.com/TechPage.aspx

[olddog]

Originally Posted by mr bruce

http://www.totalseal.com/TechPage.aspx

This is the only mention I found on that page.

Cross hatch angles can also vary depending on the application, These angles determine the critical ring rotation speed, generally a 45° cross hatch angle will do a very good job.

[Pete Munroe]

Guys,

OH, puhlleeze...it is due to CORIOLIS effect...rotation of the earth...northern vs. southern hemisphere...the guys down in Oz have similar, but opposite problem.

If you have any doubts, go flush the toilet to see which way the...ah...stuff rotates...there's the definitive answer...maybe

Crosshatch, smoshhatch...sheeshhh...

[DanEC]

Well - a follow up question. I've always heard of "stuck rings" and efforts people will go through to free them up. Never had a situation I could relate to that problem or completely understood the issue. Is this typically in relationship to the rings being carbon gummed up and no longer able to rotate?? It always seems to be attributed to an old motor that has been sitting and blowing oil or having low compression when restarted (like the thing isn't just worn out). But, I'm not clear how anyone would relate it to the rings not rotating without pulling the motor apart?

Dan

[DanEC]

Originally Posted by olddog

This is the only mention I found on that page.

Cross hatch angles can also vary depending on the application, These angles determine the critical ring rotation speed, generally a 45° cross hatch angle will do a very good job.

OK - I apparently over-shot it.

Thanks

[Woodz428]

Originally Posted by DanEC

Well - a follow up question. I've always heard of "stuck rings" and efforts people will go through to free them up. Never had a situation I could relate to that problem or completely understood the issue. Is this typically in relationship to the rings being carbon gummed up and no longer able to rotate??

Dan

There are a number of things that can cause sticky rings. You are correct in that they are mostly in older engines or ones that sat for an extended period. If they are stuck, the big problem is they can't seal the cylinder or worse they gouge one. Gummy rings from excess oil, corrosion from setting too long with a valve open allowing atmosphere to eneter with mosture, those are the most common ones I've seen.. I have also seen, though more rarely, damage to the top of the piston, whether detonation or FOD, that pinches the top ring and causes it to not function properly. Those are usually pinched at one point,though I have seen one that the whole circumference of the piston top had melted from lean/detonation and the complete top ring land was pinched.
While I have known for many years about ring movement, I doubt they actually "rotate completely around the cylinder. I would suggest that they work back and forth as they move up and down. Pulled a lot of engines apart and never saw rings too far from their point of installation. The rings are usualy still close to the installed phasing as well, so I'd have to see some that "spin" completely before I'd buy it. Of course just a little movement within a 2 stroke engine can get a ring hooked in a port and ...well I'll save the description.

[wideglidejoe]

I always figured they moved around a little, but not full rotation.

I really like the northern vs. southern hemisphere analogy!!

My theory......the drivers side bank of cylinders, the rings rotate clockwise, and the other side, they rotate counterclockwise. kinda like 392Cobra's avatar......oh wait, that's something else that's rotating.

[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.

[ACademic]

Originally Posted by redmt

How did we ever get questions answered before the internet?

You hoofed it and asked the local hot rodders or grease monkeys what they knew. Then headed over to the local service station and asked the local mechanic what he knew. If a consensus wasn't clear and you still were not convinced, then the really determined would pick up the phone and place a long distance call to someone at Hot Rod Magazine in So Cal and maybe they fielded your question (again, with their knowledge and not a manufacturer's). Or they just hung up thinking it was one of their friends making a crank call.

[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.

[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!

[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

[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.


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