In a 2-stroke petrol engine, the oil and petrol are usually mixed before they enter the engine. Different engines use different ratios, as given in manufacturer’s specifications.
Oil, air and petrol enter the crankcase. The high temperatures vaporize the petrol and the oil lubricates the moving parts.
A 4-stroke petrol engine crankshaft is basically the same as that in a 2-stroke. At first, the shape may be a surprise.
Why won’t a simpler shape do the job? It’s all to do with balancing forces.
With its weight evenly balanced, this top spins properly. By adding a magnet it now becomes unbalanced. Without removing this magnet, how can the top be made to spin properly again? Put an identical magnet on the other side. Then the weight is balanced again. The second magnet acts as a counterweight.
Counterweights appear in unusual places. They are essential for some systems to work at all.
Crankshaft counterweights help keep the rotating components in balance. They help keep the crankshaft turning as smoothly as possible.
The crankshaft turns because of the forces transmitted through the connecting rods. At the same time, it must be held in place. That’s done by bearings. They reduce friction, and allow free movement.
The Crankshaft is held in place in the engine block by main bearings at points called journals. Different bearings do different jobs These bearings support the crankshaft in place but let it turn freely. The crankshaft also needs to be located to stop lateral movement. This is done by using flanges.
Between the connecting rod and the crankshaft are connecting rod bearings. They protect the spinning crankshaft at points also called journals.
On the rear of the crankshaft is a heavy flywheel.
It stores up energy from the power stroke and helps keep the crankshaft turning. In a 4-stroke engine, only 1 of the 4 strokes in a cycle delivers power. In one cycle the crankshaft makes 2 revolutions. In a 2-stroke, every second stroke is a power stroke. Without the flywheel to store energy from the power stroke, the crankshaft will slow down and stop.
