Do rings rotate?

Chuck Sea/Tac

Chuck Sea/Tac

Well-known member
We had an interesting discussion today at the swap meet regarding ring gap, and the question came up whether spacing the gaps made any real difference, because they rotate anyway. One thought, if they don't rotate, and like many gaps, it doesn't close all the way up, wouldn't it leave a small vertical ridge as the cylinder wears? Anyway does anyone have any insight on this?
 
Rings are supposed to be installed such that the gaps don't line up from ring to ring. So if one ring tended to cause a ridge the other rings would cancel that out. That is, wear it off.
 
I see no reason as to why they would not rotate. They are not pined in place. The actual question in my opinion is how much do they rotate.

As for how come we care about spacing the gaps, we do know with 100% certainty the negative effects of a gap from the top on the piston down the side.
 
well they may rotate slightly but eventually will wear in and kinda seat themselves, if they rotated willy nilly there would be no such thing as stuck rings and would have worn out piston ring grooves in the pistons.
 
In the 60's I overhauled an engine where someone had installed the rings with all the gaps in a straight line on one piston. That cylinder had a line of metal where the rings didn't wear it away. That's the only time I've ever seen such a thing, but does show those rings didn't rotate.
 
Rings do rotate. I saw it fairly recently in an 0-200 Continental that an 'engine shop' had supposedly overhauled. The engine was returned to that shop twice for low compression and excessive oil consumption which continued.
We jerked the cylinders off it and found them tapered quite badly and the rings were lined up on 2 cylinders within 10 hours. Straightened them out, new rings and balanced the new pistons as they were out quite a bit. Engine has been running fine for about 3 or 4 years now. Knock on wood.
Maybe the engine was stuck together with those ring gaps all lined up, but, I doubt anyone would do that. But, they never took the taper out of the cylinders so who knows.
 
Years ago, I asked this same question and came to the conclusion that ,no, they didn't rotate. What would drive the rotation? would it be CW or CCW would the upper ring rotate CW while the lower ring rotated CCW? Would one ring rotate faster than the others? Wouldn't the cross hatch prevent it? Until the cylinder wore ever slowly out of round? Once the cylinder is out of round, the rings couldn't possibly rotate.
Terry
 
SeaSlugs said:
well they may rotate slightly but eventually will wear in and kinda seat themselves, if they rotated willy nilly there would be no such thing as stuck rings and would have worn out piston ring grooves in the pistons.
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Sorry, SeaSlugs, but I have to disagree. The rings will move a lot. The only way to prevent it is with a pin in the groove at the gap, which I have seen. I can't remember what engine it was, this was long ago, but I know it has been done.

And piston ring grooves will wear out from ring movement and they can become bell-mouthed. Although they can be machined square again and have a ring spacer installed, it is really time to replace the piston.

Sticking rings can result from overheating, fried oil, varnish, dirt or other Acts of God not understood by Man. Sometimes it is just plain magic. Maybe even ethanol in the gas, it does everything else. :)
 
Question! How come the ends of the the comp. rings are not "lapped" over to gain a 100% seal instead of having a ring gap? In other words, the ends of the ring would be lapped over each other and there would be no ring gap. Just askin'.
Terry
 
Motorcycle two strokes almost always had the pins in the pistions to prevent ring rotation. I think because they didn't want the ring gap to occur in the port area.



Cool Hand Lurker said:
Sorry, SeaSlugs, but I have to disagree. The rings will move a lot. The only way to prevent it is with a pin in the groove at the gap, which I have seen. I can't remember what engine it was, this was long ago, but I know it has been done.

And piston ring grooves will wear out from ring movement and they can become bell-mouthed. Although they can be machined square again and have a ring spacer installed, it is really time to replace the piston.

Sticking rings can result from overheating, fried oil, varnish, dirt or other Acts of God not understood by Man. Sometimes it is just plain magic. Maybe even ethanol in the gas, it does everything else. :)
Click to expand...
 
A guy I knew went to a tech school in the '60's. He had lots of time to play, so he built engines and mapped where the ring gaps were when assembled. Even run for a few seconds when torn down the gaps would be at a different place. The only reason for staggered placement is for initial start up.
 
JonC said:
Motorcycle two strokes almost always had the pins in the pistions to prevent ring rotation. I think because they didn't want the ring gap to occur in the port area.
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YES! That was the engine. Thanks Jon.
I raced a two-stroke motorcycle back in the 60's and tore it down many times. I should have remembered.

One thing I do remember well about those days was when the chain broke under extreme acceleration and the end of the chain came whipping around the rear wheel and snapped me on the hinder like a wet towel. I coasted to a stop on the track. Standing up. Stood up for quite awhile after that too. :)
 
It's pretty common with aircraft piston engines to see a sudden drop in compression go away after a few additional hours of operation. It was always explained as several of the ring gaps lining up. This differs from a slow degradation, which is due to wear. Of course there's many explanations for sudden losses of compression, but absent other signs of serious issues (i.e. an engine suddenly experiencing severe oil consumption, or uneven values of cylinder head temps) we would just run the engine for 10 hrs or so, watch it closely, and retest; compression would always go back to normal after a few hours.
 
Terry said:
Question! How come the ends of the the comp. rings are not "lapped" over to gain a 100% seal instead of having a ring gap? In other words, the ends of the ring would be lapped over each other and there would be no ring gap. Just askin'.
Terry
Click to expand...

Childs & Albert makes step-gapped rings.
 
Cool Hand Lurker said:
The only way to prevent it is with a pin in the groove at the gap, which I have seen. I can't remember what engine it was, this was long ago, but I know it has been done.
Click to expand...

All two stroke engines have their rings pinned to prevent rotation (and to ensure they are installed correctly in the first place). Otherwise if/when they rotate the ends will get hung up in one of the ports and BAD things will happen.

Oops, see this was already mentioned...
 
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Rings start to move around in cylinders as soon as the gaps find a worn area to move to....old worn, out of round cylinders can be found to have all ring gaps lined up......after tear down,a dial bore gauge should be used to determined if you need to hone for slight wear or a complete rebore is necessary.....
 
Please explain where does the force that rotates the rings comes from? Pistons cannot rotate. The cylinder does not rotate. So how is it you say the rings rotate in operation?
 
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