How does Crankcase work? | What is the Function of Crankcase?

An engine is a most vital part of your vehicle. It contains a crankcase, fuel system, crankshaft, piston, fuel pump, fuel injector, connecting rod, and many other parts. The crankcase is the most vital part of the IC engine. The main purpose of the crankcase is to shield the engine crankshaft. It is a part of the engine block installed below the cylinder. This article mainly explains the crankcase working, function, construction, and some other aspects.

What is a Crankcase?

The crankcase is the “body” that holds all the internal parts of the engine together. It’s the largest part of the engine but must be designed to be strong and light.

The crankcase is formed by the portion of the cylinder block below the cylinder bores and the stamped or cast metal oil pan that forms the lower enclosure of the engine and also serves as a lubricating oil reservoir or sump.


Two-stroke engines typically use a crankcase-compression design, resulting in the fuel/air mixture passing through the crankcase before entering the cylinder. This design of the engine does not include an oil sump in the crankcase.

Four-stroke engines typically have an oil sump at the bottom of the crankcase, and the majority of the engine’s oil is held within the crankcase. The fuel/air mixture does not pass through the crankcase in a four-stroke engine; however, a small amount of exhaust gasses often enters as “blow-by” from the combustion chamber.

The crankcase often forms the lower half of the main bearing journals (with the bearing caps forming the other half), although, in some engines, the crankcase completely surrounds the main bearing journals.

Construction and Parts of Crankcase

A crankcase is a metal cast case used to cover the crankshaft of a reciprocating engine. In most modern engines, the crankcase is integrated into the engine block. The crankshaft of the engine is mounted onto the grooves of the crankcase. It is an assembly.

The crankcase has the following major parts:

1) Upper Crankcase

This is the upper part of the crankcase. It carries a camshaft and valve mechanism. It has bores for the inlet and exhaust manifold where valves and valve sheets are placed. The camshaft is connected to the crankshaft via belt drive or chain drive of the engine.

2) Lower Crankcase

This is one of the main component of the engine. It is directly connected to the engine block by bolts. The lower crankcase carries the crankshaft of the engine, which is mounted onto the case, and the case is poured with oil to cool and lubricate the shaft.

The crankshaft is mounted with the help of thrust bearings which won’t let the crankshaft move from its position. One end of the crankshaft carries the dead load, which spills oil onto the crankshaft by rotating inside the crankcase.

3) Valve

The valve installs at the bottom part. This valve uses to change the oil. When you open it, the oil will flow downwards due to gravity.

Crankcase Function

The crankcase is the central component of the engine. It houses the entire crank mechanism, including pistons, cylinders, and connecting rods. Accessories, the transmission/gearbox, and the engine control system with the cylinder head are attached to the crankcase.

The main universal function of the crankcase is to shield the crankshaft and the connecting rods from debris. In simple two-stroke engines, the crankcase serves several roles and is used as the pressurization chamber for the fuel-air mixture.

In more complex four-stroke designs, it is sealed off from the fuel-air mixture by the pistons and instead works mainly to store and circulate the oil. It also works as a safety feature to keep people from moving parts, but that’s a stretch.

Advantages of Crankcase

  • The crankcase surrounds the connecting rod and crankshaft, and prevents them from damage due to contaimination.
  • It stops the entry of debris into crankshaft and connecting rod.
  • In complex engines, it helps to circulate the oil.
  • It also acts as a pressurization chamber for the fuel-air mixture.
  • This part of engine ensures a sealed enclosure to keep moisture and dirt away from the rotating components.

Leave a Comment