What is the Difference Between Two-Stroke and Four-Stroke Engines?

[DiLucas]

The difference between two-stroke and four-stroke engines lies in their valve train mechanisms and lubrication methods. Difference in Valve Train Mechanisms: In a two-stroke engine, the air-fuel mixture entering the crankcase controls the opening and closing of the intake and scavenging ports through piston movement under certain pressure, completing the scavenging and exhaust processes. In a four-stroke engine, the rotation of the crankshaft is transmitted to the camshaft via a timing chain. During rotation, the intake and exhaust cams push the rocker arms to swing, and under the action of valve springs, the intake and exhaust valves open and close at specific times. Difference in Lubrication Methods: Two-stroke engines generally use either mixed lubrication or separate lubrication. In the case of separate lubrication, components such as the crankshaft-connecting rod assembly in the crankcase, cylinder, and piston assembly are lubricated by a mist-like mixture of oil, gasoline, and air. The lubricating oil plays roles in lubrication, cooling, sealing, and cleaning within the engine, affecting component wear and service life. Four-stroke engines use crankshaft splash lubrication for the piston-connecting rod mechanism, while the camshaft, rocker arms, valves, etc., employ pump-pressure lubrication.