What is crankshaft?

July 28, 2021
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A crankshaft is a rotating shaft which (in conjunction with the connecting rods) converts reciprocating motion of the pistons into rotational motion. Crankshafts are commonly used in internal combustion engines and consist of a series of cranks and crankpins to which the connecting rods are attached.

The crankshaft rotates within the engine block through use of main bearings, and the crankpins rotate within the connecting rods using rod bearings. Crankshafts are usually made from metal, with most modern crankshafts being constructed using forged steel.

Types of Crankshaft

There are three different types of cranks you can use in an engine.
1. Cast Cranks
These types of cranks are around for a long time and are found in a lot of diesel and petrol engine. As the name suggests, these are made from Malleable Iron through a casting process.
These are pretty cheap to make and works fine too hence they are a common choice for manufacturers.
A flat plane crank is one where the journals are 180 degrees apart common in all in-line four engines. Whereas a cross-plane crank, on the other hand, needs a module of multiple parts because the journals and counterweights are not symmetrical.
Cast cranks can be flame hardened to improve wear resistance in particular areas.

2. Forged Cranks
These are a more robust crankshaft than a cast crank. They are more commonly found in higher stressed engines and come standard with some 16v engine.
A forged crank is made in a totally different way. A set of dies are machined to the approximate shape of the crank.
These dies to sit in a very large hydraulic press having a clamping force of many tons. A hot bar of high-grade steel alloy is placed onto the bottom die and the dies are closed.
Once the dies are closed the metal is squeezed in very tightly. The material is then both compacted and aligned better than the casting process.
These type cranks are also hardened like the cast types but it uses Induction Hardening.

3. Billet Cranks

Billet cranks are the best type of crank you can have in your engine if you want to get the most from it.
4340 steel is normally used to manufacture this kind of crank. This contains nickel, chromium, aluminum, and molybdenum amongst other elements.
These cranks are popular because of lowest crankshaft machining time. They also require minimal balancing due to the uniform makeup of the material.