Crankcase is attached to the bottom face of the cylinder block in I.C.engine. It acts as the base of the engine. It supports the crankshaft an camshaft in suitable bearings and provides the arms for supporting the engine on the frame. The oil pan and the lower part of the cylinder block together are called the crankcase.

The cylinder block and upper half of the crankcase are cast as a single integral unit. This casting is usually made of a ferrous alloy or semi-steel to provide a stronger and harder casting. The use of stronger and tougher material permits thinner casting valves, thus saving weight and improving cooling, although it is more difficult to machine than gray iron. Aluminium alloy is also a potentially attractive material for crankcase. This is because of its light weight, good thermal conductivity and good cooling effect.