The rotation and movement is what probably helps with keeping them clean and also delays in development of wear patterns which keeps the compression in spec for longer.
Do Piston Rings Rotate in their grooves whilst the engine's running? At approximately how many RPM?
- Thread starter Donald64
- Start date
If they didn't rotate some, I think they would wear out faster. There is some side loading of pistons in a V engine or even more in a horizontally opposed engine like a Porsche, VW, or Subaru.
Could be, that scenario is somewhat common with GA aircraft engines. I've experienced it on aircraft that I've owned, some more so than others.
I would guess that the rotation also helps prevent the rings from sticking in their grooves, losing the tension against the cylinder walls.
I suppose that will result in very even wear and ring width should be very consistent over the lifespan of the rings.
They rotate all the time. In fact, if they're not rotating, that's indication of stuck rings and/or really poor cylinder surface. I've torn apart several engines that I've built, after being run, and the rings are never where I set them. It doesn't matter the type of hone, ring thickness or tension, or piston to wall clearance. Doesn't matter if the top ring is .100" down or .350" down, if it's barrel faced or napier cut, reverse twist, etc.... they all rotate.
They did! When the British Leyland A Series A+ engine was designed, they irradiated the piston rings and then took samples of the engine oil to determine the wear rate. When I was a school science tech, I had a poster behind my desk detailing this.
I'd forgotten the technique they used to determine the rate of rotation. I wasn't expecting much response to my post, so thank you all.
But they do. And it's a good thing that they do?
In the early eighties' all of my family lost their jobs within a few weeks. We opened a car repair business and did quite a few engine rebuilds. Older low value cars were, if not too worn, fitted with AE Hepolite oil control piston ring sets. The top ring had a 'ridge-dodger' profile to clear the cylinder bore's unworn portion. Many other brands had a similar product.
They worked very well. Compression test figure
Not case closed 'proof' by any means. I'll look at my notes & bookmarks tomorrow evening. I've spent the last four hours struggling to remove a single Tork bolt from BMW E36 starter motor. Now I know why I've been putting the job off since 2020
Thanks for all of your replies.
They worked very well. Compression test figure
https://www.partinfo.co.uk/articles/292
Not case closed 'proof' by any means. I'll look at my notes & bookmarks tomorrow evening. I've spent the last four hours struggling to remove a single Tork bolt from BMW E36 starter motor. Now I know why I've been putting the job off since 2020
Thanks for all of your replies.Sorry, the link is in the title. Also the YouTube video posted by anther member, earlier.In the early eighties' all of my family lost their jobs within a few weeks. We opened a car repair business and did quite a few engine rebuilds. Older low value cars were, if not too worn, fitted with AE Hepolite oil control piston ring sets. The top ring had a 'ridge-dodger' profile to clear the cylinder bore's unworn portion. Many other brands had a similar product.
They worked very well. Compression test figure
https://www.partinfo.co.uk/articles/292
Not case closed 'proof' by any means. I'll look at my notes & bookmarks tomorrow evening. I've spent the last four hours struggling to remove a single Tork bolt from BMW E36 starter motor. Now I know why I've been putting the job off since 2020
I have observed movement in engines I have built as well. My standard ring installation pattern is always: Oil ring gap towards camshaft, top ring to rear of engine parallel to the piston pin, 2nd ring to front of engine parallel to the piston pin. When I have gone back into engines I have rebuilt, ring orientation is not the same. I can't say how many revolutions were made, what direction etc. of course, but they definitely moved. I have sometimes wondered if it even matters how I put it together given they move... 
but it is still good practice to offset the gaps in my opinion and I always will.
but it is still good practice to offset the gaps in my opinion and I always will.
But why do they rotate?
My guess would be the combined effect of the cyclic gas
A piston on the power stroke will compress the ring unevenly owing to the effect of the thrust side causing a ring to naturally rotate as the ring's gap is nearly always at an offset angle to the thrust?
Cross hatching, gas cycling forces and possibly vibration too?
I've a old Honda 50cc piston and if I repeatedly compress and very slightly release the piston rings with a simple ring compressor tool, it has a tendency to gradually progress the ring around the groove. It takes around ten cycles to visibly move the ring.
Last edited:
slightly off topic here- but some big mining companies in Australia decided to sack their truck drivers and run driverless trucks - with in a few weeks there was deep ruts in the dirt mining roads and enormous problems when the rains came - the good old human drivers "wandered" over the road way and kept the whole road compacted evenly. the stupid AI dimwits ran all trucks on exactly the same track and destroyed the roads, especially for the other smaller vehicles running around the minesite. such stupidity going to robotics en masse and depriving kids of good old simple jobs manufacturing and driving. such managerial arrogance is the death of a good living for many people.
https://www.sae.org/publications/technical-papers/content/2019-01-2366/
https://www.sae.org/publications/technical-papers/content/900224/
https://www.jstor.org/stable/44548521
https://trid.trb.org/view/1830190
Finally, not on actual piston ring rotation, but lots of links within the paper:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6630038/
Case closed?
Last edited:
That's cool
Similar threads
