I don't think it should rotate because the action of scrubbing against the
cylinder walls will wear "micro" grooves in the rings that match up against
corresponding ridges on the cylinder wall. If the rings rotated there would
never be this ridge/groove result. Since you can see and sometimes feel the
grooves and ridges, I can only assume the rotation of the ring is not
happening.

--
Jim Carter
wrote in message
om...

....

Put it another way - why shouldn't it rotate?