The Function of a Crankshaft in Engines

Imagining a reciprocating engine without a crankshaft is impossible. A crankshaft converts reciprocating motion from the piston and connecting rod into rotary motion, which is then used to rotate the propeller assembly of an aircraft. A crankshaft consists of one or more cranks placed at specific lengths where the piston is mounted. The crankshaft is placed in the crankcase on a longitudinal axis supported by a bearing between each throw.

Crankshafts need to be extremely strong for proper energy conversion and reliability, so they are often forged using some of the strongest alloys, such as chromium nickel molybdenum steel. They can be constructed in two ways, using either single-piece  or multi-piece construction methods. Furthermore, the number of throws in a crankshaft depends on the engine. For instance, if the engine is a single row type, then a single-throw crankshaft will be used. Meanwhile if the engine is a twin-row type, then a two-throw crankshaft will be applicable. Similarly, there are four-throw and six-throw crankshaft types available for four-cylinder horizontally opposed engines, four-cylinder inline engines, six-cylinder inline engines, 12-cylinder V-type engines, and six-cylinder opposed engines, respectively. Moreover, the crankshaft is a significant part of the reciprocating engine. Irrespective of the number of throws, every crankshaft has three crucial components: a journal, crankpin, and crank cheek. Apart from these, counterweights and dampers are attached to the crankshaft.

A journal provides a point where the connecting rod connects with the crankshaft. The main bearing offers the necessary support, rotating with the crankshaft. It is also helpful in determining the throw or the stroke of the engine. Generally, the throw or stroke can be calculated by measuring the distance between the crankshaft's center and the crankpin journal's center. The crankpin is a hollow part and is generally off-center from the prominent journals at the point where the connecting rod is attached to the crankshaft. A crankpin and two crank cheeks combined are called a throw. The crankpin's hollow structure helps reduce the overall weight of the crankshaft and assists as a passage for the movement of lubricants such as oil.

The crank cheek is critical in connecting the crankshaft to the leading journal. Therefore, it must be made of a sturdy material and have enough rigidity. Additionally, the crank cheek often has a counterweight on its opposite end to help support the crankshaft and keep things balanced. Sometimes crank cheeks are drilled, making passages for the oil to be sprayed on the cylinder walls. The crankshaft is the central machinery component that allows an engine to run efficiently. While there are many types and sizes for such elements, they must all match up with their corresponding cylinder arrangement.


A crankshaft is crucial for an engine to function, and if you are looking for a crankshaft or any other aircraft parts, get in touch with NSN Unlimited. As a parts distributor for aviation and marine industries, we are the latest platform where you can get all the parts you require. Our inventory has a wide array of products, ranging from engine components to GSE tools. With 100% quality assurance, we can quickly get our customers new, used, obsolete, and even hard-to-find components. Contact us for more details, and one of our dedicated account executives will serve you with quick and competitive quotes in 15 minutes. In addition, we offer 24/7x365 customer service.


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