This is the most common engine design found in street motorcycles today. It refers to the number of times a piston moves up and down through each power cycle. 1) A downward stroke brings in the fuel/air mixture; 2) an upward stroke compresses the fuel/air mixture; 3) a downward stroke results when that mixture is ignited and expands, and finally; 4) an upward stroke expels the exhaust gases.

an internal-combustion engine in which an explosive mixture is drawn into the cylinder on the first stroke and is compressed and ignited on the second stroke; work is done on the third stroke and the products of combustion are exhausted on the fourth stroke

Internal-combustion engine operating on the Otto cycle principle of intake, compression, expansion and exhaust.

The staple configuration of virtually every piston car engine. As each piston goes up and down there are four stages in the process: intake, where combustible gasses are sucked in; compression, where the gasses are squeezed before combustion; the actual combustion of the mixture, and then exhaust as the burnt gasses are forced out again.

an internal combustion engine which works on four-stroke cycle, ie power is developed once every four strokes compare two-stroke engine

An engine in which the piston travels up and down twice to achieve combustion. Produces more torque (power) than 2-stroke engines of similar size, as well as a more “scale” sound, greater economy and the ability to swing bigger props. Less common than 2-stroke engines, but more often used in large- or giant-scale airplanes. Where engine requirements for a kit are listed, 4-stroke engines are usually the second range listed and marked as such. See also Two-Stroke Engine.