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An internal combustion engine (which is also called a four-cycle engine) in which an engine block (which also has water cooling chambers within the block) houses several cylinders, each having a piston, which is attached to a crankshaft by a connecting rod, and an inlet (intake) and outlet (exhaust) valve. The piston moves twice up and twice down the cylinder, making four separate strokes, with each stroke being 180 degrees of movement, therefore two complete revolutions of the crankshaft. Ignition is either by a spark plug in petrol engines or through compression of air (which increase the temperature within the cylinder, and this ignites the atomised diesel fuel) in diesel engines. The majority of vehicles and turf machinery are 4-stroke engines, with increasing numbers of electric battery powered items becoming available since 2020, whilst many smaller handheld items, such as trimmers and hedge cutters are two-stroke, or battery powered.

The sequence of the four-stroke engine is as follows:
1. The initial stroke, usually called the induction stroke, starts with the piston at the top of the cylinder, referred to as top dead centre (TDC). As the piston starts to move downwards, the inlet valve opens and draws in (by suction) a mixture of air and fuel through the inlet port, which originated in the carburettor. When the piston reaches the bottom of the cylinder, the top of the piston is now at bottom dead centre (BDC) and the inlet valve is now closed.
2. The second stroke is called the compression stroke. This starts at BDC and moves upwards compressing the mixture of fuel and air, finishing at TDC. Both the inlet and outlet valves are closed during this stroke.
3. At the third stroke, which can be called either ignition, power or combustion stroke, the compressed mixture is initially ignited by the spark plug in a petrol engine or the heat created by the compressed mixture in a diesel engine, and with both valves staying closed, the piston is forced downwards. The crankshaft will be connected to a drive shaft to power a machine.
4. The final stroke is called the exhaust stroke. With the piston now starting at BDC, the inlet valve staying closed whilst the outlet valve opens, and the exhaust gases (from the burnt fuel) are expelled through the open outlet valve and outlet port. When the piston reaches TDC for the second time, this completes one instance of the four-stroke process and the engine is ready to start again with the induction stroke.