The position of the piston is just as crucial in this 2-stroke diesel engine. Its exhaust valve must open and close at the right point in the engine cycle.
In one 2-stroke engine cycle, the crankshaft makes one revolution. How does this compare with a 4-stroke engine cycle? How many revolutions does its crankshaft complete from Intake, through Compression, Ignition, and Power, to Exhaust? It makes two revolutions. In that time, what happens to the valves? They open and close once. So the cams must make just one revolution. And if the cams make one revolution, so must the camshaft.
But in each 4-stroke cycle, the crankshaft rotates completely twice. So the camshaft must rotate at half the speed of the crankshaft. This can be achieved by gears.
Take two gears with teeth the same size - one with forty teeth and the other, the driving gear, with twenty. When they mesh, the larger one rotates at half the speed of the smaller one. The gear with twice as many teeth turns at half the speed of the other.
These gears turn in opposite directions and the one with fewer teeth rotates faster. Now let them be separated but linked by a chain. They turn in the same direction, at the same speeds as when they were meshed.
If the smaller gear is attached to the crankshaft and the other to the camshaft, how fast will the camshaft turn compared with the crankshaft? It will turn at half the speed. Just what the system needs.
Everything happens at the right time. The piston leaves top dead center, the crankshaft turns, and the camshaft turns too. The cam acts on the rocker arm. It opens the valve - as required.
This is a 2-stroke diesel engine. How many revolutions does the crankshaft make in one cycle, from Intake, Compression, Ignition, Power to Exhaust? It makes one revolution. During that revolution, the valve opens and closes once. The camshaft makes one revolution too.
Camshaft and crankshaft must rotate at the same speed.
The gears must be the same size.
The power stroke pushes the piston down. The crankshaft turns, as does the camshaft. The cam acts on the rocker arm, which opens the valve - at the right time.
