Crankshaft:

The crankshaft transforms the linear motion of the pistons into a rotational motion which is transmited to the load. These are made of forged steel. The forged crankshaft is machined to generate the crankshaft bearing and connecting rod bearing surfaces. A rod bearings are eccentric or offset, from the middle of the crankshaft as described in Figure. This offset converts the reciprocating (up and down) motion of the piston within the rotary motion of the crankshaft. An amount of offset determines the stroke (distance the piston travels) of the engine.

The crankshaft does not ride straightly on the cast iron block crankshaft supports, other than rides on special bearing material as display in Figure. The connecting rods also have bearings inserted among the crankshaft and the connecting rods. A bearing material is a soft alloy of metals which gives a replaceable wear surface and avoids galling among two same metals that is crankshaft and connecting rod. Every bearing is split into halves to permit assembly of the engine. The crankshaft is drilled along with oil passages which permits the engine to feed oil to each of the crankshaft bearings and connection rod bearings and up into the connecting rod itself.

The crankshaft has huge weights, known as counter weights that balance the weight of the connecting rods. These weights guarantee an even (balance) force in during the rotation of the moving elements.

Figure: Diesel Engine Crankshaft and Bearings