what is there difference between a ringed and non ringed engine? Is one or the other better?

There have been a lot of threads on this in the past, so this is the "short answer".

The obvious answer is that a ringed engine has a piston ring, while a non-ringed engine doesn't.

Most (but not all) non-ringed engines are of ABC or ABN construction (both of which I'll just call ABC).

ABC engines are broken in differently than ringed or some other construction types.

Ringed engines can last longer than ABC types, and are usually more tolerate of dusty envrionments. ABC engines usually produce a slightly higher RPM than a ringed engine. (I don't know if anyone still does, but years ago, you could get the same engine from OS and some others in ringed and ABC variants. The ABC type usually put out a tad more power, and was a tad more expensive. Which is funny, since ABC engines are actually less costly to make than ringed engines, though that might not have been the case then).

However, the bottom line is that for the most part, for 99% of flyers, there is little or no real world difference between the types in day-to-day flying, and there are a bunch of different types and configurations out there, more than ringed/non-ringed would indicate.

I've got an old OS MAX .49 from about '62. The guy at my hobby store had some strange name for its type of piston head, the top of the piston is the ring, but it looks like an ABC motor.

Montague's answer is terrific (as usual), and I'll add just one more bit of info; in addition to lasting longer, a ringed engine will usually take quite a bit longer to break in.
Dennis-

I really can't comment on which type of engine lasts the longest since mine usually last until I'm tired of them and something newer and "better" comes out.

It is my opinion the reason nearly all 2-strokes are ringless, ABC type construction is the flood of new fliers and the reluctance of most to break in their engines. In this nearly instantaneous world, we don't went to run tank after tank of fuel through an engine to get it to run correctly, we want to go right now.

With a ringed engine, you risk warping the ring if you don't run it somewhat rich at the start. Slobbering rich for a couple of tanks is better and a gallon rich is best. I did this to all my Saito 4-strokes and they run great.

An ABC engine, for all practical purposes, is very hard to hurt if you drop it in a plane, lean it out and go fly. Running it rich is bad for engines of this type. So the manufacturers are probably thinking that it's worth the slightly higher manufacturing costs of the ABC type to let people crank up and go. They probably don't get as many returns or complaints, either.

Joe Doaks can put his new Widget .46 in his new fun fly plane, crank up and by the time he has a couple of trim flights on the plane, the engine is mostly broken in and reaching max power.

His buddy with the ringed engine, a 4-stroke, for example, is still putzing around, running rich while Joe is scooting around the sky.

LEDZx,
I think you might be talking about a engine with a Dykes ring on it. That type has the ring near the top edge of the piston, or actually overlaps the top edge. Don't see those around too much.

Jesse

That's it whstlngdeath. Its amazing to see the amount of knowledge you can gain just from one thread.

uhh montague?
while ringed engines are more tolorate of dusty conditions ringed engine put out more power and rpm than abc. let me explain why.
let's say that your piston on an abc engine is an inch from surface to the bottom of the skirt. that means that all that is rubbing on the side walls. on a ringed engine, the ring is in most rc cases, an eighth inch tall, so, using the one inch piston thing, you have one eighth the contact on a ringed engine and therefore have less friction and resistance resulting in more power. that extra power is usually put out in higher rpms. it is like going to a smaller prop. for instance, the os .46 fx and .50 sk ringed are made from the same materials, same case, same intenal parts, but the .50 is .04 cubic inches larger. it is also ringed. it produces 15% more power than the .46. that .04 ci isn't enough to justify all that gain in power. i have both engines. the .46 turns a 10x7 at the same rpm (give or take a few just because it isn't the same engine) as the .50 when turning an 11x7 prop

On the contrary,
The only location that a ABC piston seals the bore is at the top of the stroke. The bore of the cylinder is tapered, being narrower at the top. The piston is "loose" in the bore until the top of the piston reaches the pinch point at the top of the bore. A ringed piston's
ring is in constant contact with the entire length of the bore from top to bottom, which would be in constant friction. The ABC seal at the top of the piston is greater than the seal of a ringed piston, giving you more compression. All of this assumes that the piston to sleeve fit is good on the ABC type and that the piston to bore fit is good on the ringed type.
Also, the internal components of a ABC engine, (sleeve mainly), is made of a different material than that of a ringed engine.

Jesse

he also mentioned abn. the 46 fx is abn. all i know is on the same amount of nitro and a .04 ci difference, when broken in the same on the same fuel the .50 has more power. besides the ring, the internal parts of the two are the same.

Ringed engines have more friction when running than ABC/N engines. Believe me on this one. Take the OS .40 FSR. They made two versions, a ringed version and an ABC version. They were identical except for the pison and liner. The ABC engine was more expensive but put out more RPM.

In your case, there are more differences between those two engines than you think there are. They don't appear to share the same crankshaft or connecting rod. For your statement to be the same, the stroke of both engines would be the same, the .50 would just have a larger bore. In fact, the .50 has a stroke of .847in compared to just .770 for the .46. I looked at the parts listings and specs on www.osengines.com

On the other hand, the .40FX and .46FX ARE the same engine with just a larger bore on the .46, both have a stroke of .770, but the .46 has a .06in larger bore (.810 vs .870)

So comparing the .46 and the .50 is a non-starter, they're way to different.

whstlngdeath is right on in his description.

So, being a novice, I have to voice an opinion...

I have done a fair amount of reading, and yes, the bore of non-ringed engines is "conical" in that it is slightly narower at the compression end of the stroke.

The reasoning for this is *not* to get better compression/seal, but because a running engine is hotter at the top than at the bottom (the combustion happens at the top of the stroke, and cools throughout the descent). Thus, the top end of the cylinder head expands more than the lower end, and thus the heat of the combustion expands the con-shape into a cylinder, or as near as dammit!

The intention is to make the "conical" cylinder a cylinder with expansion.

Then again, I may be wrong.

gus

I know you can replace the ring on an engine after it's worn out, but can you renew/replace the piston on an ABC? I reckon it will cost more to replace the piston. Am I correct? Will the ABC engine cost more to maintain due to a higher price in piston v.s. ring?

You can, in fact replace the piston and liner of an ABC engine (or a ringed engine for that matter). But in an ABC engine, I've always heard you replace them together. So it does cost more than just replacing a ring on a ringed engine. On the other hand, I suspect it's actually rather rare for an engine to actually get "worn out". Most, it seems, die from other causes long before normal wear.

Gus, I think you are right about the why of the taper. I was agreeing with the fact that the effect of this is that the surface friction of an ABC engine is lower than a ringed engine when running. I've seen that written more than once by guys who know a lot more about engines than I do. I'm under the impression that the taper plays a part in that, though I could be wrong on the overall effect of the taper.

Well I'll weigh in here by saying my personal preference is for a ringed engine (given the option). I'm not concerned about the longer and more critical running in required because I value the longer life the far more dirt tolerant rings will give and then the far cheaper cost of overhaul when it's needed. On that point it should be noted that where you can just buy a ring by itself, you can only get a matched ABC piston/liner because they're not available seperately.

One area where ABC is better though is at extreme high revs (20K+) because rings can start to flutter which wears out the ring groove. Piston drag (friction) is virtually the same though no matter what type of set up is used because all drag comes from the parasitic drag of the oil film and not metal to metal contact. Any additional drag (enough to noticeably reduce power output) would be converted into heat and yet both ABC and ringed run at much the same temperatures.

I guess what it comes down to as far as the original question goes is that if you're a typical modeller who just wants to get out and fly with the minimum fuss and buys a new engine because the latest one is a different colour then an ABC will suit perfectly.

I make over 200 model engine rings for most model engines. Email for details. Thanks Frank
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