ABC/Non-Ringed: These letters stand for aluminum, brass and chrome (or a composite, such as nickel). “ABC” engines have an aluminum piston and a chrome or composite-coated brass cylinder sleeve, which improves their efficiency and performance. They have no piston ring and rely on a very tight piston/cylinder fit. Because of the tight fit, it is very important that the engine is broken in properly.

After-Run Oil: Lubricant worked through an engine between runs and before storing it for the winter. After-run oil prevents varnish and gum build-up and protects engine parts from rust and corrosion.

Air Filter: Also called “air cleaners,” they serve the same purpose on R/C car and truck engines as they do in full-size automobiles — to capture dirt and dust before it can infiltrate and damage the engine. Many use foam or paper elements that must regularly be replaced, or removed and cleaned, so that air can easily pass through.

BB: These letters indicate that the engine features a ball-bearing supported crankshaft — which makes the engine run smoother and last longer.

Carburetor: The part of the engine which controls the throttle setting, and allows you to adjust the mixture of air and fuel for proper combustion.

Crankshaft: When the piston pumps up and down, it turns a shaft called the crankshaft. The turning crankshaft transfers power out into the model —whether to an airplane’s propeller, a boat’s driveshaft, or a car’s gears.

Cylinder Head: The tallest part of the engine, marked by ridges or fins. The ridges increase the head’s surface area, which allows more air to circulate past it and draw away heat.

Cylinder Sleeve: The channel inside the cylinder head in which the piston moves up and down.

Four-Stroke (Four-Cycle): Although a 4-stroke engine has less power than a 2-stroke engine of comparable size, there are advantages to 4-stroke engines. They produce a quieter, more realistic sound than most 2-strokes. They can swing a bigger prop than the same size 2-stroke engine (this is an asset in large, slow-flying aerobatic and scale models). Lastly, the fuel economy is better.

Fuel Overflow Line (Vent): Several “lines” (of tubing) enter or leave a model’s fuel tank. This is the line through which fuel will overflow when the tank is full.

Fuel Pick-Up Line: The line in the fuel tank through which fuel travels to the carburetor. Typically, it’s a flexible tube with a weight or “clunk” on the end. The weight keeps the line submerged in fuel no matter how the model is oriented. This is also the line through which the tank is filled.

Glow Plug: The heat source that ignites the fuel/air mixture in the engine. A battery is used initially to heat the glow plug’s filament. After the engine is running, the battery can be removed. The wire filament inside the plug is kept hot by the “explosions” in the engine’s cylinder.

Glow Plug Clip/Battery: A 1.5 volt battery, which is connected to the glow plug on a model’s engine for starting. The battery is removed once the engine is running steadily.

Idle Bar Plug: This type of glow plug has a “bar” across the tip to help prevent raw fuel from being splashed onto the glow element. Too much raw fuel will cool the plug and prevent it from igniting the fuel/air mixture. Most plugs are now designed without idle bars, to avoid any risk of the bar falling off and into the engine’s cylinder.

Laydown: Refers to a car engine designed without a tall cylinder head — the engine “lays down” in the chassis, cooled by a fan unit. Laydown engines boost the realism of the model and help lower its center of gravity to hold to the track better.

Mount: Engines rarely bolt directly to a model; usually, they are fastened to an engine mount which is attached to the model. The crucial benefit of engine mounts is that they absorb some of the vibration created by the running engine — vibration which could otherwise weaken the structure of the model itself.

Muffler: A device attached to the exhaust stack of the engine to reduce noise and increase back pressure, which helps low-speed performance. Note: Most R/C clubs require the use of mufflers.

Muffler Baffle: A plate inside the muffler which reduces engine noise. This plate can be removed to increase power, but only if there are no noise restrictions where you fly.

Needle Valve: Adjustment on a carburetor used to set the proper fuel/air mixture for combustion. Some carburetors have separate needle adjustments for low and high throttle. Typically, turning the needle clockwise leans the mixture (allows in less fuel), and turning it counter-clockwise richens the mixture (allows in more fuel). However, there are a few exceptions — refer to the engine manufacturer’s instructions.

NiCd Starter: A self-contained battery and glow plug clip, used when starting the engine (see Glow Plug Clip).

RE: These letters stand for Rear Exhaust, in which the muffler is positioned behind the engine. Such a setup decreases drag in airplanes, and may also be necessary with certain car chassis layouts.

Remote Needle Valve: (See Needle Valve) An engine with a remote needle valve increases the pilot’s safety by enabling him or her to make adjustments well out of the way of the spinning propeller. The Tower Hobbies .46 ABC is one example of such an engine.

SE: These letters stand for Side Exhaust, in which the muffler is positioned to the side of the engine.

Tuned Pipe: Similar to a muffler in that it reduces the noise output of the engine; however, a tuned pipe also boosts power and speed by using sound wave pressure and reflections to increase the amount of combustion mixture.

U/C or C/L: A U-Control (or Control Line) engine has no throttle and runs wide open until it is out of fuel under the category of “radio-control.”

Water Cooling Jacket: Method used with marine (boat) engines to reduce operating temperatures. The boat’s propeller forces water into a “pickup tube” which leads to and coils around the engine’s cylinder head. That cool water absorbs the heat of the engine. It’s then routed back into the lake or pond.