4cycle

4cycle, commonly written as 4-cycle or four-stroke, denotes the four-stroke cycle used in many internal combustion engines. The term describes engines that complete a power-producing cycle in four piston strokes over two crankshaft revolutions: intake, compression, power, and exhaust. During intake, the piston moves down, drawing air-fuel mixture through the intake valve; during compression, the piston moves up, compressing the mixture; the power stroke follows ignition, pushing the piston down; finally, exhaust expels burnt gases as the exhaust valve opens.

Historically, the four-stroke cycle was developed by Nicolaus Otto and others in the late 19th century, becoming the standard for automotive and many other engines due to its efficiency and smoother operation compared to two-stroke designs.

4-cycle engines are widely used in automobiles, motorcycles, lawn and garden equipment, generators, and some aircraft. They typically use a lubrication system and can incorporate various valve configurations (inlet/outlet) such as overhead camshaft (OHC) or overhead valve (OHV) designs, as well as pushrod architectures.

Compared with two-stroke engines, four-stroke engines generally offer higher fuel efficiency, lower emissions, and longer service intervals but tend to be heavier, more complex, and more expensive to manufacture. Maintenance centers on valve clearance, timing, and lubrication.

Terminology varies; some sources write 4-cycle or four-stroke, while marketing names may use 4cycle as a brand or product line. The term can also appear in contexts describing engine technology rather than a separate entity named "4cycle."