Two-stroke engine

A two-stroke engine completes its working cycle in two strokes of the piston, which is one revolution of the crankshaft. As the piston rises, it compresses the mixture above it while drawing fresh mixture into the crankcase below. After ignition, the piston moves down, uncovers the exhaust port and then the transfer ports, which push the fresh charge into the cylinder.

There are usually no valves or camshafts; ports in the cylinder wall do the job, often with a reed valve and an exhaust power valve. The result is a light, simple engine with a lot of power for its size, popular in enduro, motocross, trials and older scooters.

Lubrication comes from oil mixed with the fuel (premix) or injected separately. Use the correct ratio and two-stroke oil, and follow the manual's top-end service intervals.