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One of the most critical components of the internal combustion engine is the crankshaft. Unfortunately, very few vehicle owners understand what crankshafts are and how important they are in their automotive engines. But with a little bit of education, and a better comprehension of basic terminology, we can explore the importance of these vital engine parts together.

A crankshaft sits within the engine block and is secured with main caps. The crankshaft main journals run perfectly in line, which allows ideal placement in the engine block. Between the block and the crankshaft are engine bearings, which are composed of a variety of materials including aluminum outer and steel backings. The connecting rods, which are what the pistons attach to, are secured to the crankshaft in the same manner as the mains. The distance between the engine bearings and the crankshaft is known in the industry as oil bearing clearance and in most cases approximately .003″ is desired. This allows ample room for the oil to lubricate these reciprocating parts and helps to extend the life of the entire engine.

Problems with oil are typically what leads engine bearings to fail. These conditions may be the result of dirty oil or oil starvation. When the engine bearings are not properly lubricated, they will come into direct contact with the crankshaft journals and begin breaking down. As bearings lose their outer aluminum coating, the wear will quickly cut into the copper and steel backings. This can result in serious damage to the crankshaft. Additionally, the particles being distributed throughout the engine can also harm the engine block cylinder walls and other components which are dependent on oil.

When crankshafts are only slightly worn, they can be repaired by a process called crankshaft grinding. By grinding the journals on a crankshaft, this engine part can be reconditioned for use with thicker bearings. Badly damaged crankshafts may also be repaired, but typically require that the severely damaged journal be welded prior to grinding.

When crankshafts are too severely damaged for repair, or a performance upgrade is required, vehicle owners do have aftermarket options available to them. Generally speaking, there are three types of crankshafts available including those that are made from cast, forgings and billet steel. Below I will explain more about these options and how a specific type of crankshaft may be more ideal for your engine.

Cast Crankshafts

As the name implies, cast crankshafts are made from castings. Molten iron is poured into a mold to make the engine part. This is a quick and efficient procedure for manufacturers to produce engine parts. Unfortunately, cast iron shrinks when it cools and may also contain voids. The voids and shrinking during the cooling process create conditions of weakness within the part. Regardless, cast iron crankshafts are ideal for most ordinary automotive engines as they are not required to handle the stress from the production of high horsepower.

Forged Crankshafts

In the automotive performance industry, forged internal engine parts are quite common because they are much stronger then those parts which have been cast. Forged crankshafts are normally made with alloy steel, which is much stronger than cast iron. This alloy steel is heated and then mechanically forced into a crankshaft die to produce the forging. With a superior alloy steel being forced into a die, forged crankshafts are capable of handling the horsepower produced by modern day performance engines. The most commonly forged crankshafts are made with 4340 steel and also 4130 steel.

Billet Steel Crankshafts

Unlike the casting and forging process, billet steel is never molten and is actually machined from a large chunk of steel. While billet steel crankshafts can be far superior to even forged crankshafts, ultimately their strength is determined by the material used to manufacture the crankshaft. It is quite common to see 4340 billet steel crankshafts available in the automotive performance industry, but other materials may be used as well. Billet steel crankshafts are ordinarily only used by those in the professional automotive racing industry and in extreme horsepower engines.

With a greater understanding of the crankshaft, and the different crankshaft options available to vehicle owners, you are better prepared to understand how important this engine part truly is. Additionally, references to the different types of crankshafts will provide you with a better understanding of the terminology used to describe crankshafts and other internal engine parts which were produced using different materials and manufacturing processes.