As the title and if they do, what average RPM?
Do Piston Rings Rotate in their grooves whilst the engine's running? At approximately how many RPM?
- Thread starter Donald64
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Not really. I suppose they can and that is why 2 stroke stuff has a pin holding them but once it is assembled they don’t go anywhere much.
I would expect piston rings to move fractionally sideways in both directions but I cannot see them developing consistent rotation. In two-stroke engines, ring gap pins prevent the rings from rotating.
I thought, with little evidence, that the whole notion if ring “seating” was to wear away small amount of ring and cylinder wall metals to create a near-perfect seal at each point. Any rotation would compromise this seal.
Does the width of a piston ring change relatively evenly over its lifespan?
Hi, yes in some applications piston rings rotate, at least in common recip aircraft engines. The result can be a temporary increase in oil consumption if the gaps align, but that should cure itself. I would expect the same in other engines unless they are positively located.
Yes they rotate.
Many years ago when Cadillac switched to robotic assembly of engines the robots were designed with software that put all of the gaps in the piston rings aligned. The result was that a batch of engines was produced with the gaps all aligned that had very high oil consumption. It was so bad that Cadillac had to do a recall and the fix was that the tecks at the dealers had to take the engines apart and rotate the rings on all the Pistons so that none of the gaps aligned. Imagine having to rip an engine down just to access the Rings to change the positioning of the gaps. But that is what they had to do. Of course they change the software from then on so that whenever robots assembled the engines the gaps in the piston rings were no longer aligned. So I guess the Rings don't really rotate that much because if they did the problem would have gone away without having to rip the engines apart and redo the positioning, and it didn't.
Correct, they do indeed rotate. In most conventional engines at a rate of around 4-8RPM. The Cadillac story is interesting btw. My source is Modern Engine Technology, Heinz Heisler. A truly excellent 300+ page read, available on eBay for under $10 from time to time. The actual rate of rotation took some time to find and was from an SAE paper, when I had access to them. Thanks for the replies and interest.
I would suggest the alignment of the rings created a raised ridge, effectively pegging the rings?
Interesting, as the paper I read stated they do rotate. I once had eight Citroen XUD Diesel engines in bits. I messed up on rebuilding one and ordered a 1.7 head gasket for a 1.9 engine. Upon starting, a faint tapping noise could be heard. I drove the car over the weekend and on Sunday evening, I remembered what I'd done wrong. Upon stripping the engine one piston had contacted the gasket, so I removed it. The rings were close to being perfectly in alignment, even though I'd spaced them equally, avoiding gaps at the thrust face...
Even after nearly 45 years working on cars, I still have a keen interest and learn even more as time goes by.
I’ve reassembled plenty of engines and clocked the rings according to the manufacturer’s instructions. Torn down plenty also and never observed rings stacked. For large stroke industrial engines I’d assume there maybe some rotation. Automotive not so much. There would be random fouled plugs, skipping, and inconsistent idle smoothness due to loss of compression if so. If rings are rotation an automotive engine there’s excessive piston to cylinder clearance.
We find the rings to be in a different position than installation. So, yes, they rotate. However, a cylinder with a significant wear pattern may hold the rings stationary.
I read that paper a long time ago, they used radiotracer technique to observe rotation.
Tell that to the diagonal crosshatch that’s sliding across the rings at a couple thousand feet per minute. To rotate 8-10’ over 3-4000 feet traveled is nothing.
Sometimes someone will post that an engine suddenly used oil. Then mysteriously quit using oil. Did the rings line up for a while?
That is quite possible, if the ring lands get varnish and carbon it can cause sticking of one or all of the rings.
Do the rings rotate continually in the same direction or do they rotate fractionally in either direction?
The way I understand it they are all over the place CW/CCW, faster and slower and a more aggressive cylinder crosshatch pattern can increase the movement.
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