An engine’s camshaft controls the operation of the valves in a cylinder head. Without it, the engine won’t work.
To understand how the valves work, you need to know a little about how a typical four-stroke engine operates. The first step is intake, where the fuel/air mixture is introduced to the cylinder as the piston descends into the cylinder. The second step is compression, where the piston rises in the cylinder to pressurise the fuel.
It is then ignited with a spark plug (gasoline) or self-ignites (diesel), forcing the piston back down. The fourth stage is exhaust, where the piston rises again and the spent fuel/air mixture is expelled.
The fuel/air mixture is admitted and the exhaust gases are expelled to/from the cylinder through respective intake and exhaust valves, and it’s these that are controlled by the camshaft.
The opening and closing of the valves is achieved by asymmetrical lobes that are fitted to the to the camshaft, so when the shaft rotates the valves operate in a certain order.
The camshaft is connected to the crankshaft (which is driven by the operation of the pistons) by the timing belt, so the operation of both is closely intertwined.
If the timing belt or chain should snap while the engine is running, the pistons may hit the valves, causing extensive damage.
This is why it is so important to check the condition of the belt on a regular basis and to change it at the manufacturer’s prescribed intervals.
Some larger modern engines have dual overhead camshafts, where one camshaft operates the intake valves and the other controls the exhaust valves.
This is often done to increase the number of valves per cylinder, which increases the engine’s power output.