What is a crankshaft in a car engine?

This blog post will answer the question, ‘What is a crankshaft in a car engine?’, and cover topics like, components that make up a crankshaft, method of manufacturing a crankshaft, crankshaft defects, and crankshaft maintenance.

What is a crankshaft in car engine?

The crankshaft of an internal combustion engine receives the power from the pistons down to the connecting rods via the crank pins. The crankshaft is responsible for converting the reciprocating motion into rotating motion which helps turn the wheels of the car.

The crankshaft mounts in bearings that encircle the journals to help them rotate freely. The crankshaft is made of high carbon steel by the forging process.

Components that make up a crankshaft

These are the following components that make up a crankshaft.


There are two kinds of crankshaft journals, main journals, and connecting rod journals.

Main journals

They are also known as the main bearing journals and the engine rotates around these same journals. These journals are machined to retain completed roundness and a smooth texture. They are placed into saddles, in which a bearing insert is fitted. The journal is bolted by the main bearing cap which is bolted and sealed according to a particular torque specification.

Connecting rod journals

These journals attach to the freely rotating and larger end of the connecting rod. They are also known as crank pins. These journals have grooves made into them to provide a pathway for lubricant to enter the connecting rod and get sprayed into the cylinder.


They are also called crank throws and determine the distance between the main bearing journal and the center of the crankshaft. This distance helps in understanding the range of motion the piston has.


They act as a link between the rod and the main bearing journals.


They are also referred to as counterweights and act as balancing weights for the crankshaft because they suffer a lot of rotational forces and need to stay intact to supply power to the wheels.

The counterweights help balance these rotational forces out so that the crankshaft is able to run smoothly and also at high speeds without any power loss.

Method of manufacturing of a crankshaft

Generally, cars are equipped with an iron crankshaft that is made by pouring molten iron into a mold cavity. 

Performance cars, on the other hand, use forged crankshafts that are made by heating a steel block until it appears red hot, followed by the application of high pressure on it to form it into the desired shape.

After the forging or casting process of the crankshaft has been completed, the bearing journals are sent to be machined to achieve top-quality smoothness. This is followed by the drilling of the oil pathways. 

This entire manufacturing process must aim at making the journals tougher and sturdier than the bearings as they are irreplaceable and cannot suffer any kind of damage. This is done by hardening these areas by using heat treatment.

Crankshaft defects

These are the following visible defects that can occur in crankshafts.

Crankshaft faults

Although a rare occurrence, crankshaft faults are caused when the engine is subjected to extreme conditions or is unable to handle the current operating load.

Journals are worn out

This mainly occurs due to inadequate oil pressure and causes the journals to rub against the bearings and suffer wear and tear, thus causing the oil pressure to decrease and the clearance between them to increase.

Crankshaft fatigue

Continuous exposure to high-intensity rotational forces results in the formation of fractures on the crankshaft. These are usually located in the areas where the journals meet the web.

The process of magnafluxing can be used to check for the presence of cracks in the crankshaft and hence, determine the structural integrity of the crankshaft.

Crankshaft maintenance

The wearing of crankshaft main bearings and journals occurs due to the following reasons:

  • Lack of oil
  • Scratches by dirt in the oil’Poor seating in the bore
  • Out of round bearing or journals
  • Fatigue

Precision insert type main bearings are mostly used in modern automotive engines, which can be easily replaced without replacing the crankshaft.

The oil pressure leak detector is used to determine any oil leaks in the main bearings.

When the bearing wear seems to be uneven, then remove the crankshaft from the engine block and check both separately for alignment and clogged air passages.

To compensate for excessive clearance caused by a worn crankshaft journal, an undersized bearing must be used. If the journals are found to be worn more than 0.0125 mm to 0.325 mm, a new crankshaft needs to be used.

To check for crankshaft alignment, use a dial gauge by supporting the crankshaft on V-blocks. The crankshaft is rotated in V-blocks and the dial indicator shows signs of misalignment. A bent crankshaft can be straightened using a heavy press.

The bearing surfaces of the crankshaft are finished to extreme smoothness. Journals and crankpins are ground to fit the next undersized bearings available.

While servicing the crankshaft, it should be thoroughly cleaned by means of a suitable cleaning solvent. Oil passages should be cleaned by using a rifle-type brush. The bearing surfaces should be immediately reoiled after they have been cleaned to protect them from rusting.

Research has shown the different types of crankshafts that have been produced to date.


This blog post addressed the question, ‘What is a crankshaft in a car engine?’

We came across the various components that make up a crankshaft and the methods of manufacturing them depending on the desired build of vehicle. Furthermore, steps for crankshaft maintenance have also been provided. Please feel free to comment on the content or ask any questions in the comments section below.

Frequently Asked Questions (FAQs): What is a crankshaft in a car engine?

What is the strongest type of crankshaft?

The strongest type of crankshaft is the billet steel crankshaft.

Which is the best crankshaft?

The best crankshaft used in high-performance vehicles is the 4340 chrome-moly and it is the strongest due to the presence of nickel and chrome in it.

What is the function of crankcase?

The crankcase acts as a housing for the entire mechanism of the crank along with the pistons, the engine cylinders, and the connecting rods.