Ringed Engines vs. ABC Engines

Many R/C Engines come in both ABC and Ringed versions. The ABC type engine has an Aluminum piston, a Bronze cylinder sleeve, and Chrome plating on the cylinder sleeve or a variation where Nickel plating is substituted for the Chrome plating. These engines have a tapered cylinder which changes to a non-taper when at operating temperature.

The other type of engine is the ringed engine. This engine has a piston ring. The cylinder is not tapered. It is the ring which prevents gas from passing by the piston (blow-by). The ring has spring tension which forces it against the cylinder wall at all times. This is why it is not necessary to taper the cylinder walls during construction. There is one other important difference. The cylinder walls are not plated bronze. Instead, they are constructed of a porous metal. This means that it has many tiny holes in the metal structure. During engine operation, carbon from the burnt gases will begin to fill these holes on the surface of the cylinder. This carbon makes an excellent lubricant. The piston ring is not porous.

What does this mean to the user? The ABC type engines can typically withstand more heat before they are damaged. More horse power is available from these engines if the fuel mixture and prop sizes are changed to push the engine harder. However, because the cylinder walls are tapered at low temperatures, they can be harder to start.

The ringed engines start easily since the ring prevents blow-by even when the engine is cold. However, all of the friction in a ringed engine takes place at the ring itself, a relatively small area. Also the porous cylinder material does not dissipate heat as fast as the bronze cylinder in the ABC type engine. This means that the engine is more easily damaged by too much heat.

Because of these characteristics, you can expect that the safe operating temperature range of the ringed engine to be shifted lower than the ABC type engine. This means that the ringed engine will require good lubrication at high r.p.m. Since castor oil has a much higher flash-point than synthetic oil, your fuel should contain at least some castor oil. You should also avoid running your engine too lean.

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