there's a page on rings here:
www.fme-cat.com/TechTips.aspx?brand=Sealed Power

I have no idea why I can't post the link correctly, it's like the site won't allow the word 'Power' in a link.
Add a space and the word 'Power' to the link in your address bar after you click on it.

Piston compression rings seal on the inside top edge and the bottom outside edge of the ring lands under compression and just the opposite when the is cylinder firing or on the intake stroke, I think. That is what I have figure out anyways, So here goes on the rings sealing and breaking in, as the crankshaft, pistons and rods rotate the pressures inside the cylindes change on every stroke from sucking in and pushing up or down, the piston stops twice on each stroke so there is negative pressure on the rings and piston ringlands, they float in the transession from up to down motion So that is when the rings can rotate a small amount in the ringlands. I have assemble and dyno tuned a lot of motors and then took the motors apart for inspection before racing them or giving them to the customer. I have seen rings move all the way around the pistons, I have also seen them end up with the rings gaps aligned on some cylinders and not on others I'm sure that at some time the rings stop moving or rotating in the ringlands, but maybe not IHTHs BTW, I have taken race motors apart after several hundred runs for inspection that leak down well, had no damages to the cylinder walls, pistons or rings so I put back together and race them some more Some of them went over four hundred runs + bracket racing before needing reringing and honing That is with the air cleaners on and good maintenance on the engine

What will it do to a new motor if the valves stop working on a cylinder for a while? Like if the rockers break and don't work on a cylinder. And it is run for a while before it is fixed. Ronnie

An easy way to visualize this is handrails on stairs.
Notice that older ones are smooth where many hands have glided on them?
They are seated.
If you want another example, look at a door threshold that has the seal. It's also worn in or seated.

Its my opinion that once the ring is "seated" it
doesnt rotate... I believe thats the part you are
having a hard time with...again my opinion... the
first time the engine fires up, the flame front and
the way the pressure builds moves the rings some then
its there for good ..................JMO

Doggonit, Rapid! I just spent a half hour reading most of the entire post! There were a lot of interesting points and one confirmation of my idea of squish. This guy is a lot like Smokey Yunick before he began to believe himself to always be right.

R.

They seat by taking the car out and doing a big juicy burn-out. That's how they "seat"

It's easier to think of them as sealing. The motoworks url above gives a good explanation. The ring has to seal between the ring and the land, and between the edge of the ring and the bore. It seals or seats by coming in very very close to the surfaces it's sealing against. There should be a very thin film of oil between all three surfaces.
There is an unbalanced radial force from the cylinder pressure that loads the ring against the cylinder wall. Think about it. Pressure from the cylinder pushes outwards on the ring while once it is in very very close contact with the cylinder wall there is no pressure pushing it back. I believe the ring is "seated" when the cylinder wall and ring outside edge has worn to let them exclude pressure from the cylinder.
The force of the gas on the ring pushes it against the ring land to seal the sides.

In modern times piston manufacturers like Mahle have found that making the ring lands extremely flat, like within 6 millionths of an inch, increases power by giving a better seal. The radial edges are designed to wear in quickly. The rings also twist when in service which is probably why a new compression ring has very sharp corners, those would be the intended wear points.

The only rings that do not move on a piston are either stuck or there is a pin stuck in the ring slot by a designer. Long ago I read that certain chevy race engines of the early '60s had a problem with ring wear because the rings would spin too rapidly. But rings, like valves, will rotate by themselves.

Keep in mind that the rings are wearing at the cylinder walls when the walls are loaded by bolts or studs and hot. I believe they actually make the cylinder more round in its true operating condition.

R

Here's one I like to refer to:
http://www.ktm950.info/how/breakin/engine_breakin.html

Based on teh info it contains, the earlier question of 'what happens to a cylinder where the valves don't open?'.

I think that cylinder would not get seated, as the high pressure of combustion pushes the rings against the walls for seating, and seating = sealing. The oil film would stay on teh wall and the rings would glide over and glaze it.

RodStRace is right on the money with his analogy. Rings scuff against the crosshatch surface in the cylinder and "bed" themselves in to form a seal. why it is so important to have a plateau finish on your cylinder walls if running any kind if moly rings.

All good and correct info the only part not covered are the different types of rings ie: reverse torsional,bevel back,beveled. all rings will rotate. If you have a vibration problem you'll find them all the gaps coming to the same point. The rings seat at the ring land as well as the bore surface. They use a combination of physics already in place in the cylinder,as well as the film of oil in place on the cyl wall. Would reusing old ring work? I suppose it could but I've never tried it in two stroke engines. Too much work to take a chance.