What is a Crankcase and What Does it Do?

What is Crankcase In an Engine?

A crankcase is the housing for the crankshaft in a reciprocating internal combustion engine. In most modern engines, the crankcase is integrated into the engine block. It also functions as housing and protects the engine parts against dust, water, and splashing mud.

The crankcase stores lubricating oil required for lubricating the engine parts. The size of a crankcase is sufficiently large as it accommodates the revolving crankshaft with the connecting rod.

Various accessories like a carburetor, fuel pump, generator, water pump, air cleaner, starting motor, fan, oil filter, oil body of cooler, etc. are also mounted on the crankcase.

The crankcase not only gives support to the engine parts and engine mountings, but also withstands the loads caused by piston thrust, gas pressure, primary and secondary forces, couples, etc.

Therefore, the crankcase must be strong to withstand these loads and pressures. When the cylinder block and the crankcase are cast together in one unit, grey cast iron is used because it has rigidity, low cost, and high wear resistance.

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.

An open-crank engine has no crankcase. This design was used in early engines and remains in use in some large diesel engines, such as used in ships.

crankcase

Types of Crankcases

The cylinder block and the upper part of the crankcase are from an integral cast. Thus, a crankcase is usually divided into an upper and a lower section. The lower section is known as the ‘oil pan’ and acts as a reservoir for the storage of lubricating oil.

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The lubricating oil is splashed due to the rotation of the crank and is also pumped to the engine bearings, thus lubricating the various engine parts. For cooling the lubricating oil, fins or ribs are provided on the outside of the oil pan.

These fins also increase the strength of the oil pan.

The joints between the upper section of the crankcase and the oil pan may be either on the level of the crankshaft axis or below this axis. The assembly of the upper section of the crankcase with the oil pan has been shown.

The main forces acting on a cylinder block are due to:

  • Gas pressure includes the force of the explosion, and
  • Inertial forces due to reciprocating masses.

Both these forces act along the connecting rod, i.e., the line of stroke. These forces tend to lift the cylinder blocks from the crankcase.

Therefore, in the case of a single-cylinder engine having a crankcase joint on the axis of the crankshaft, resisting forces are induced in the threads of the retaining bolts used at the joints. Note that the angularity of the connecting rod results in the horizontal forces on the cylinder walls and the crankshaft bearing.

Decreasing the length of the connecting rod increases the side forces. In the case of a multi-cylinder engine, the resulting stresses are divided between a greater number of bolts. In the case of 90° V-type engines, the component of stresses is equally divided in vertical and horizontal directions.

Therefore, the crankcase is split through the crankshaft axis. Such assembly makes the crankcase lighter because the oil pan size is increased which is usually made of aluminum alloy.

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To minimize the resisting forces in the bolts used in the crankcase joint, the upper section of the crankcase is further extended below the axis of the crankshaft. The extension is from 50 mm to 75 mm below the crankshaft.

This decreases the size of the oil pan, but the crankcase rigidity is increased in the vertical direction. The upper section of the crankcase takes up the force of the explosion, whereas the oil pan bolts take only inertial forces.

A four-stroke cycle engine needs a heavier flywheel than a two-stroke cycle engine. Therefore, the crankcase of the four-stroke cycle engine is more robust than the two-stroke cycle engine. An engine following a mixed cycle has a high compression ratio and a large force of the explosion and therefore needs a stronger crankcase.

FAQs.

What is the crankcase in an engine?

The crankcase is the “body” that holds all of the other engine parts together. It’s the largest part of the engine, but must be designed to be both strong and light. To keep the weight low, the brothers used aluminum to make the crankcase. The crankcase was cast at a foundry in Dayton.

What is a crankcase and what does it do?

An intrinsic component of an internal combustion engine, the crankcase is a drilled metal frame that houses several parts, notably the crankshaft. Its main universal function is to shield the crankshaft and the connecting rods from debris.

Is crankcase oil the same as engine oil?

engine oil (crankcase oil, motor oil) – oil carried in the crankcase, sump, or oil pan of a reciprocating internal combustion engine to lubricate all major engine parts; also used in reciprocating compressors and in steam engines of crankcase design.

Where is the crankcase located?

The crankcase is usually located on the bottom of the cylinder block. The crankcase is defined as the area around the crankshaft and crankshaft bearings. This area encloses the rotating crankshaft and crankshaft counterweights and directs returning oil into the oil pan.

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What is an ignition of a crankcase?

The ignition can be caused by the same “hot spot” which caused the oil mist. If a large amount of oil mist has developed before ignition, the burning can cause a tremendous rise of pressure in the crankcase (explosion), which forces a momentary opening of the relief valves.

What is the purpose of crankcase ventilation?

A crankcase ventilation system removes unwanted gases from the crankcase of an internal combustion engine. The system usually consists of a tube, a one-way valve and a vacuum source (such as the intake manifold).

Does engine oil go into the crankcase?

Unlike other types of engines, there is no supply of oil to the crankcase, because it handles the fuel/air mixture. Instead, two-stroke oil is mixed with the fuel used by the engine and burned in the combustion chamber.

How much does it cost to replace the crankcase oil filter?

On average, expect to pay between $200 and $300 to replace your crankcase breather filter. Note that the parts alone will cost you about $100 to $105, and expect to pay a labor cost of between $90 and $120.

Is crankcase cleaning necessary?

You probably don’t need a crankcase flush. The vast majority of engines on the road are quite clean inside, and will stay that way as long as their maintenance is kept up. Change your oil regularly; use a quality filter; and you’ll be just fine.

What is the difference between engine block and crankcase?

The cylinder heads are integrated into the engine block, but the crankcase is separate. The bottom half of the crankcase also includes the oil sump.