I would like to know what are the main differences between ringed and ABC engines and which one you prefer.

At the same size/brand. Which one is more powerful, durable, easy to handle, etc?

Thank you.

Jose Jimenez.
Club Aeromodelismo Madrilenio.
Mostoles - Madrid - Spain

The only one of your questions that can be given an answer that almost can't be disputed is engine life.

A ringed engine, given proper care, is almost impossible to destroy or wear out. The best of the ringed engines have a chrome plated cylinder bore. All Saito and many K&Bs have the chromed sleeve and ringed piston.

I just did an overhaul on a 30 year old Saito, all I had to replace was the piston ring, bearings, and the valve springs. That made it essentially a brand new engine. It's not uncommon to see a 40 year old K&B 61 still running like new.

If made by hand the ABC engines would be more expensive than ringed engines dur to the required precision, but CNC machinery has brought the price below the ringed engines. ABC uses an Alunimum piston in a Brass Chrome plated sleeve. The sleeve bore is tapered a small amount, being smaller at the top. At normal running temperatures the top is hotter than the bottom, if the taper is right at the running temperature the bore is straight when the engine is warm. While an ABC engine can be ringed, generally "ABC" refers to a lapped fit piston. The lapped piston ABC design gives good engine life and quick break-in. Probably the most common model engine type currently on the market.

AAC is a variant on ABC, substituting aluminum for the brass sleeve. Same characteristics as ABC.

ABN is a cheap variation on ABC, instead of using a chrome plating it has nickel plating on the sleeve. Thunder Tiger has given excellent service with ABN, and their selling price is low, probably in a large part because of the inexpensive ABN process. OS. the other current user of ABN, has a continuing problem with failure of the plating which effectively ruins the engine due to the excessive price of repair parts. Side note: The OS engines with ringed pistons are still of good quality and long engine life. ABN is cheap to make, and is easily damaged.

The early Norvel/AME engines used a variant on ABN, substituting aluminum for the sleeve, becoming AAN. They no longer build any AAN engines.

Other material and construction methods are still in use, but I think I've pretty well covered what you asked about.

Bill.

Does that mean my O.S. LA engines are junk prone to fast wearout? I should try to buy FX or AX in the future?

Who makes the AAC engines?

Enya has made AAC engines in the past, the .11CX is one example (the newer Ultra is ABC though).

Parra makes both AAC, ABC and steel/iron (you can choose) for their .15 engine.

Jett and Enya are the only two manufacturers that utilize AAC cylinders that I personally know of. If money were no object, AAC is the way to go. Similar to a lapped iron piston in a steel liner, they will last virtually forever with the proper care and good fuel. AAC is an upgrade to a Jett, true ABC is the standard with those guys, though some models only come AAC.

The most common ringed engine I've seen are the Super Tigres. They are great engines for the price but take a long time to break in.

Why does breakin take so long?

Aren't Saito engines AAC?

I think some are, but I don't own or have ever owned one to know one way or another.

The rings are pretty hard and take awhile to seat. Until they hit around 2-3 gallons of fuel, they have to idle high and transition is usually a little blubbery rich. The carbs require a little more finesse to get adjusted properly as well.

Enya was the first to use AAC in mass production way back in 1974 with their 60X (also their first Schneurle ported). The Bluebird range (called Brat in America) from .21 to .45 were also AAC but for some reason their .51 is ABC. The Norvels were what was called AAO because they used an alloy piston and liner but the liner was plated with aluminium oxide which is otherwise known as a ceramic liner.

There should be no noticeable difference in power or handling between two identical ringed or ABx type engines but AFAIK only OS offer this with their ABN plane engines or the optional ringed heli engine. Talking about OS though, one thing I found interesting was that their top of the line Hanno Special started life as an ABN but later became a ringed engine with the Hanno II.

Given a choice, I'd prefer ringed unless it's for very high speed (20K+?) use where rings will start to flutter in the groove.

OS LAs are great engines; just not hotrods. I have the series before the LA and it just keeps running. 20+ years old; on my sons trainer. No lean runs and a little castor in the fuel and it will last about 3 airplanes.

Yes, all are AAC except for one. I think that is a twin, but I forget which engine.

Ibeliever the K&B Sportster is AAC. LAengines are notorious for wearing out liners quickly, also the FX series. In my experience it takes about a gallon of fuel in most engines (except OS) to make them run well.

The K&B Sportster engines use a unusual high silicon alloy in the cylinder/sleeve. But they chrome the piston instead. But barring abuse or inadequate oil lubrication the Sportster engines hold up really well. A big plus was that the cylinder and piston costs are quite reasonable too.

The Russians did produce model engines using a ceramic coating on the cylinder wall. Norvel used this as well as some engines that Fox Manufacturing produces too.


Now then the piston ring is the main limiting factor in getting more speed or RPMs out of a engine. Depending on the engine displacement and the ring thickness there is a RPM limit than when reached the ring begins to flutter and stop sealing properly. A variation was the Dykes rings that are much more thin and use the combustion pressures to help force the ring into the cylinder wall, thus they can get a moderate increase in RPMs using the Dykes rings. Years ago people noticed with the conventional lapped piston engines that they could get more RPMs than a ringed engine could. That lead to the development of ABC engines with a more tapered cylinder that was chromed and a special high silicon content piston that was carefully fitted to it. The more radical tapered bore of the cylinder expands when hot to become more straight, while the piston doesn't expand that much and maintains a more precision fit in the cylinder bore. Thus they got even more performance out of the ABC engine setup like that. Then CNC methods came along enabling more mass production to take over.

Generally the ABC engine will develop more power and turn higher RPMs than a ringed piston engine.
Generally a ringed piston engine will last longer than a ABC engine, but a ABC engine, that is well taken care of, can last about as long as a ringed engine can.
A ABC engine is more tolerant of a engine running too lean or overheating than a ringed engine. If a ABC engine overheats the cylinder expands more than the piston does and the piston to cylinder fit loosens up and the engine looses power before it can sieze or be galled.
A ringed piston engine tends to be much more forgiving of dirt or debris scratching the cylinder walls than a ABC engine and tends to produce its power for a longer time like that.
With CNC machining methods a ringed engine can be made with interchangeable cylinder sleeves and pistons. But a ABC engine requires the cylinder and piston to be carefully matched with each other.

The point is, "ringed engines" are also AAC, ABC, etc.

The OP's question is ambiguous.

Another difference between ringed and ABC/ABN/AAN/AAC non-ringed engines is that the non-ringed engines depend on temperature for a proper piston/bore fit. Prolonged idle, such as a long final, allows them to cool down to a less-than-optimum fit. Ringed engines have no such issues, therefore, all else being equal, they idle better. Plus, it is far cheaper to "freshen-up" the compression with a new ring than to buy a new P/L set. Also, for those of us that love the older O.S. SF-series engines, Frank Bowman makes rings that are at least as good as the hard to find OEM rings. Less expensive, too.