Just wanted to see some discussion on 1 ring VS 2 ring engines. I have had both and there doesn't seem to be a power difference. What would be the +'s and -'s of either design?

2 ring: Better compression, lasts longer between re-builds.
1 ring: Easier to break in? Cheaper?

Single ring - less friction, but the wrist pin better be located at the right height in the piston or you'll experience severe piston skirt scuffing.

Twin ring - less compression loss from blow by. More friction. A little harder to assemble.

I don't know which is easier to break in. I would think both rings on a twin would break in at the same time, but I don't know for sure.

I never noticed a difference either. Have had both designs in many different engines.

Most ringed glow engines have a single ring. They run fine.

2 rings also help transfer heat faster

single ring makes more power because less friction

Single ring will have more piston slap and sooner than a 2 ring piston will.

Bill, Waco Brother #1

One ring is enough for me.

Early two stroke engine designers found that single ring pistons had a measurable advantage over 8000 rpm and double ring pistons better at lower rpms. This can still be observed in many modern designs. Single rings should be fine for a model since propellers impose little load below top rpms.

Engines running under more demanding loads deal with heat better using twin rings.

I think single ring pistons would be an advantage over dual rings in our airplanes because the prop puts a constant load on the engines. With a constant load the vapors will build up between the rings and form carbon deposits more rapidly than most other uses 2 cycle engines experience.
That said if all out performance is wanted it's my opinion a dual ringed piston will have better compression, leading to more consistent power. And more power.

Did you ever see a 3 ring RC engine. Well here is a photo of the one that I have. I don't remember the displacement but it will turn an 18x10 prop about the same as a G-38. It starts very easy by hand and is about the smoothest single that I've run. I think this is due to the fact that it is well balanced and weighs 7 pounds. It uses points and is called a Kioritz. Compression is great. I believe the original use was as a backpack blower. They were popular in the late 70s and early 80s.

You have to admit, it's real hard to wear out engines. Especially the older designs. Easy to destroy one through misuse though.

Do you have any preference for ring count T.O.M.? I know you like 3 dubbs.

With proper ring design/material selection there will not be a big difference in engine performance unless it is a very high speed engine (10000 RPM) and higher. There are many ring designs and ring materials, as piston speeds go up with the higher performance engines, ring type selection gets more critical, for example many high speed engines use quite narrow piston rings to prevent ring flutter, the practiced ear can hear sometimes ring flutter, it can produce a distinct exhaust note warble, when this happens power definitely falls off.
Some high speed engines run fairly close piston skirt to cylinder wall dimensions so piston rocking with a single ring is greatly reduced in those cases.

For other engines, keeping the cylinder round under increased cylinder temperature (because of all the ports) could show a greater gain in power than the selection of a one ring design over a two ring design.

Joe,

Most single ring engines work just fine. The twin ring engines make a better showing on hot running or long endurance stuff. I really don't have an engine preference, they only have to work the way they are supposed to for a long time.

WRK- very interesting.

Yeah no kidding. Thanks for that info WRK.

There was a, (somewhat), popular weed whacker conversion engine that came out with a thinner single ring back around 2001. Eventually the thin ring became less favored than the older thicker ring. By then the conversion engines were moving more into cheaper chain saws.