Do piston rings rotate on the piston?

[olddog]

Some where in this thread someone mentioned that what pressure leaks past the first compression ring is trapped by the second compression ring. If I recall correctly they said something to the affect of the pressure trapped between the two rings, pushes the top ring off the land causing it to flutter and loose it's seal. Maybe they didn't exactly say this, but it was how I interpreted what ever was said. I think this is along the lines of what Barry_R is talking about.

What about using one gap-less and one normal compression ring? Has this been tried? I'm not sure if the top should be the gap-less or not, but it would seem the logical place.

[DMXF]

Originally Posted by olddog

What about using one gap-less and one normal compression ring? Has this been tried? I'm not sure if the top should be the gap-less or not, but it would seem the logical place.

I recall that is the standard gapless configuration, they all use one gapless and one gapped compression ring. Various manufacturers have tried the gapless in different grooves and I think the top groove is the one most people feel is optimal (?).

[Dominik]

In his book Power Secrets Yunick elborated around the gap and power loss, and 20 years ago when I read it, lost me.

It relates to a more than linear (cube?) loss depending on the gap. I shall dig out that book.

I did, and he also wrote about rings spinning in the grooves (or was is Bill Jenkins?):


Page 50, center column
Smokey Yunick's Power secrets

"If the head gaskets, the rings and the valves are all sealed tightly, there should not be very much leakage when the the high-pressure air (from a leak-down tester) is fed into the cylinder. It is not possible to gain a 100% mechanical seal in the cylinder, but if everything is in top notch condition, there should not be more than about 4% leakage.

..., if the average is over 8%, you don't have an engine,...

This doesn't sound like much to worry about, but you have to remember that only 1/3 of the heat energy (pressure) developed by each cylinder is actually going to push the piston down. So, if 8% of the cylinder pressure is leaking away, you are theoretically losing 24% of the recoverable flywheel horsepower."