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Crankcase And How It Works

What is a Crankcase?

A crankcase is an integral component of internal combustion engines, providing housing and structural support for key engine parts like the crankshaft, connecting rods, and pistons. It also contains the engine’s lubricating oil, which is essential for reducing friction and dissipating heat generated during engine operation.
Construction and Parts of Crankcase
A crankcase serves as a protective enclosure for the reciprocating engine’s crankshaft and related components, often integrated within the engine block.
1. Upper Crankcase: The upper crankcase constitutes the upper section of the crankcase assembly. It houses the camshaft and valve mechanism, featuring bores for inlet and exhaust manifolds, where valves and valve sheets are positioned.
2. Camshaft: The camshaft connects to the crankshaft through belt or chain drives.
3. Lower Crankcase: The lower crankcase directly secures the engine block using bolts. It serves as the foundation for the engine’s crankshaft, providing support while being continuously lubricated and cooled by the circulating oil.
4. Crankshaft Mounting: Thrust bearings ensure the crankshaft remains securely in place, preventing movement. One end of the crankshaft carries the dead load, distributing oil as it rotates inside the crankcase.
5. Valve: It is positioned at the bottom part of the crankcase. The valve serves as an oil drain, facilitating the flow of oil when opened, allowing it to drain due to gravity.
Types Of Crankcases
Crankcases come in various types to accommodate the diverse needs of different engine designs. One common classification is based on the number of pieces comprising the case. Monoblock or single-piece crankcases are cast as one unit, providing structural integrity and simplicity.
The various types of crankcases are:
1. Dry Crankcase: A dry crankcase is a type of engine design where the crankshaft and connecting rods operate in an enclosed space that is entirely separate from the engine’s lubrication system. In this setup, oil is not present in the crankcase, and lubrication is achieved through oil pumps and channels that deliver oil directly to critical engine components. Dry crankcases are commonly found in many modern automotive engines, offering advantages in oil control and reduced internal friction.
2. Wet Crankcase: In contrast to a dry crankcase, a wet crankcase incorporates oil directly into the crankcase housing. The crankshaft, connecting rods, and other moving parts are partially submerged in oil, providing continuous lubrication and cooling. This design is often seen in two-stroke engines, small gasoline engines, and some older automotive engines. While it simplifies lubrication, it can lead to oil contamination and increased internal drag.
3. Semi-Wet Crankcase: A semi-wet crankcase strikes a balance between the dry and wet designs. In this configuration, the crankshaft and connecting rods partially dip into an oil reservoir, which ensures adequate lubrication without submerging the entire assembly. Semi-wet crankcases are seen in various engines, including some motorcycles and recreational vehicles, offering the benefits of both wet and dry designs.
4. Closed Crankcase: A closed crankcase refers to an engine design where the crankcase is sealed and isolated from the environment. This closed system prevents the release of engine emissions into the atmosphere, making it environmentally friendly. Closed crankcases are common in modern, emission-compliant automotive engines, helping reduce pollution and meet stringent environmental standards.
5. Open Crankcase: An open crankcase design allows the engine’s interior to be in direct contact with the surrounding atmosphere. While this setup simplifies engine construction and cooling, it can result in the release of unburned hydrocarbons and emissions into the air, making it less environmentally friendly. Open crankcases are typically found in older engines and some small equipment engines.
Advantages of Crankcase
The advantages include:
1. The crankcase serves as a protective enclosure, safeguarding the connecting rod and crankshaft from potential contamination and damage.
2. It effectively blocks the ingress of debris, preventing it from reaching the critical crankshaft and connecting rod components.
3. In intricate engine designs, the crankcase plays a vital role in facilitating the circulation of oil, ensuring proper lubrication.
4. It functions as a pressurisation chamber, aiding in the management of the fuel-air mixture within the engine.
5. This essential engine component establishes a sealed environment, effectively shielding the rotating elements from moisture and dirt infiltration.
Function of a Crankcase
1. The crankcase stands at the heart of the engine, providing shelter for the entire crank mechanism, including pistons, cylinders, and connecting rods. Additionally, it serves as the anchor point for various accessories, the transmission/gearbox, the engine control system, and the cylinder head, all connected to the crankcase.
2. A fundamental and consistent role of the crankcase is safeguarding the crankshaft and connecting rods, effectively shielding them from potentially damaging debris. In simpler two-stroke engines, the crankcase undertakes multiple functions, doubling as the pressurisation chamber for the fuel-air mixture.
3. In more intricate four-stroke engine designs, the crankcase is hermetically separated from the fuel-air mixture by the pistons. Instead, its primary function becomes the storage and circulation of oil, which is crucial for engine lubrication. Additionally, it plays a role in enhancing safety by preventing access to moving parts, albeit to a limited extent.
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