A four-stroke engine, or internal combustion engine, has four separate processes that follow on from one another in order to produce power. These steps are: induction, compression, power, exhaust. Quite simple, in principle, but technically a fair bit more complicated than a two-stroke engine, as many more moving parts are needed to make the engine produce useful work.

The four-stroke engine has a piston connected to the crankshaft via a con rod and moves up and down in the cylinder. The crankshaft transmits this rotational movement to the gearbox which drives the rear wheel. On the first stroke, the intake valve located in the cylinder head is opened, so that the fuel-air mixture is sucked into the cylinder. At the same time, the piston is pulled down to the bottom of the cylinder bore by the crankshaft. In the next step, the second stroke, the intake valve is closed, the piston is forced up and the fuel-air mixture is compressed in the cylinder head. The intake and exhaust valves are opened and closed by cams, driven via a toothed belt or timing chain by the crankshaft.

On the third stroke, the power stroke, the four-stroke engine delivers actual work. The spark plug sparks, causing the compressed fuel-air mixture to ignite and burn with explosive force. The piston shoots back down due to this conversion of chemical energy into mechanical energy. On the fourth and final stroke, the exhaust valve opens, the piston moves upward again, pushing the resulting exhaust gases out of the cylinder, and then the entire process starts all over again.