Why does a cam shaft run at half the speed of the crankshaft?

Answer 1

The four strokes of a four-stroke engine are intake, compression, power and exhaust. The crankshaft controls the upward and downward motion of the pistons. The camshaft controls the opening and closing of the intake and exhaust valves.

Intake stroke- the intake valve is open and the exhaust valve is closed. The piston moves downward, decreasing the pressure in the cylinder, which draws the fuel-air mixture in through the intake valve.

Compression stroke- both the intake valve and the exhaust valve are closed. The piston moves upward, compressing the fuel-air mixture. When the piston nears TDC (top dead center), the fuel-air mixture is ignited by the spark plug.

Power stroke- both the intake valve and the exhaust valve are closed. The explosion caused by the ignition of the fuel-air mixture (combustion) forces the piston downward.

Exhaust stroke- the intake valve is closed and the exhaust valve is open. The piston moves upward, forcing the gases produced by combustion out of the cylinder through the exhaust valve.

So, for each firing of a given cylinder, the intake valve opens once and the exhaust valve opens once. But, for each firing of a given cylinder, the piston must travel downward and then upward twice (in each direction.). Therefore, the crankshaft must rotate twice per given cylinder firing, while the camshaft rotates only once per given cylinder firing.

Answer 2

The Camshaft turns half as fast as the Crankshaft.

Answer 3

The camshaft controls the valves, each pair or set of four controls one cylinder. One cylinder fires at a time, which rotates the crankshaft.