Do piston rings rotate on the piston?

[olddog]

Originally Posted by FWB

this is some tech from a abrasive manufacturer

Crosshatch
Crosshatch is also important because the amount, depth and angle of the crosshatch in the cylinder bores determines how much lubrication the rings receive and the rate of ring rotation.

Excessive shallow crosshatch angles can hinder or slow down the necessary ring rotation that allows the rings to dissipate heat. It can also leave too much oil on the cylinder wall allowing the rings to skate over the surface and the engine to use oil. Too steep of a crosshatch angle may not provide enough oil retention and can result in dry starts and premature ring wear. A steep crosshatch angle can also create excessive ring rotation that accelerates ring and piston groove wear.

Ring manufacturers typically recommend a crosshatch angle of 22° to 32° as measured from horizontal and uniform in both directions.

Can someone please explain how a ring rotating is going to dissipate heat? Unless explained, I say myth busted.

If the cross hatch is perfectly uniform in both directions, the drag forces of the cross hatch will be equal in both directions, therefore the opposing forces will cancel, yielding no rotation.

I have pulled engines back down, and the rings had moved. Yes, I believe they can rotate. I also pulled an engine down that burned oil from day one, with ~5000 miles on it. All ring gaps were in a straight line on all 8 pistons, as the assembler admitted he did and didn't know any better.

I suspect they move because the cross hatch is not perfect. I do not believe they rotate at any considerable speed by design or necessity. Where is myth busters when you need them? I'm not a believer that they need to rotate or for that matter that they continuously rotate. I'm thinking it is kinda random.

Well second thought some movement might be nice to keep the gaps from wearing a line in the cylinder. So some movement is desirable.

Happy to be proved wrong and open minded to learn.