What's the difference between two-stroke and four-stroke

Different structure: The hot part of two-stroke motorcycle is mainly composed of cylinder head, cylinder, piston and piston ring. The hot part of a four-stroke motorcycle is mainly composed of cylinder head, cylinder head cover, cylinder, piston, piston ring and valve train.

The valve mechanism consists of valve, valve guide, valve seat, valve spring, valve cam, valve chain, valve sprocket, chain tensioner, rocker arm and other parts. Comparatively speaking, a two-stroke motorcycle is smaller, simpler in structure, lighter in weight and easier to manufacture and maintain than a four-stroke motorcycle.

The working process is different: the crank of a two-stroke engine rotates 360 degrees to complete a working cycle, that is, the crank rotates once, the engine burns and does work once, and it completes the intake and exhaust process through the scavenging port and exhaust port on the cylinder wall. The crank of a four-stroke engine rotates 720 degrees to complete a working cycle,

Because the crank of two-stroke engine rotates once to do work and the crank of four-stroke engine rotates twice to do work, the torque of two-stroke engine is more uniform than that of four-stroke engine.

At the same time, under the condition of the same crankshaft speed and working volume, the output power of two-stroke engine is twice as high as that of four-stroke engine, but the actual output power of two-stroke engine is only 50% ~ 70% higher than that of four-stroke engine because of scavenging loss and effective working stroke reduction during ventilation.

Working principle of four-stroke engine;

Intake stroke:

When the piston is at a specified crank angle before TDC, the intake valve opens and the combustible mixture is sucked into the cylinder. When the piston moves from the top dead center to the bottom dead center, the exhaust valve closes at a certain crank angle at the top dead center, and at the same time, the volume of the cylinder above the piston increases, which makes the cylinder form a vacuum degree, and the combustible mixture continues to be sucked through the intake valve.

When the piston travels to the specified crank angle after the bottom dead center, the intake valve closes, and at this time, the intake process ends.