The crankcase is a central component in the engine. It is a drilled metal frame that houses several parts – the entire crank mechanism including the crankshaft, the pistons, cylinders and connecting rods. It also proctects everything from debris.
Accessories, the transmission/gearbox, and the engine control system with cylinder head are attached to the crankcase.
The crankcase is the most complex part cast part in a combustion engine. Thisi s because it has numerous oil and cooling channels that are required for, you guessed it, cooling and lubricating the engine.
It is worth mentioning that all engines, as part of their normal operation, allow small amounts of unburned fuel and exhaust gasses to escape into the crankcase. This collective material is known and refferred to as blow-by.
This is where a positive crankcase ventilation valce, or a PCV valve, is employed as part of an overall pressure control system to regulate de amount of blow-by ejected from the crankcase. The expelled blow-by that passes through the PCV valve is returned back to the intake mainfold, where it is reused in the combustion process.