Do piston rings rotate on the piston?

[DMXF]

Originally Posted by olddog

I don't understand - my lack of knowledge, I'm sure.

Ring loading variations caused by cylinder pressure changing with the throttle position?

or

Gap-less rings have a variation in loading due to their nature/design?

How data is interpreted can be an art all in itself. Some comparisons I've heard about used a gapless style that has opposing notches at the ends of the compression ring gaps with the thin parts overlapping. These rings tend to be thicker/heavier than other gapless designs because of the stress concentration from the discontinuity of the notch. Most input I've heard is that the weight is the main factor in any dynamic anomolies. This makes sense because if it were due to lack of gap alone, a standard ring should have the same problem in circumferential areas where there is no gap. In addition feedback is that engine builders in the top eschelons of racing simulate a gapless design by having the ends virtually butt (they close it up till they see evidence of rubbing after use, then open up a couple of thousandths from there), so if gapless in itself were a problem they would see it there too.