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Crankshaft: Function, Design & Importance (Explained)

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Last Updated on: 16th November 2023, 01:35 am

The vehicle crankshaft plays a crucial role in an engine’s operation. Its primary function is to transform the linear movement of pistons into rotational motion, driving the wheels of a vehicle.

In this article, we delve into the design of the crankshaft, function, types, and more.

crankshaft engine part

Design & Components

A crankshaft is composed of several key parts, including the following.

  • main journals
  • rod journals
  • counterweights
  • thrust bearing faces
  • crankshaft webs

The main and rod journals are where the bearings of the crankshaft are located.

The counterweights are used to balance the crankshaft, while the thrust bearing faces help control its movement along the axis of rotation, stabilising it.

Lastly, the crankshaft webs connect the main journals to the rod journals.

Crankshafts are commonly made from cast iron or forged steel due to their high strength and resistance to wear and fatigue.

These materials provide the durability required to withstand the high rotational speeds and pressures encountered during operation.

Function & Importance

At the heart of a combustion engine, the crankshaft plays a vital role in converting the linear motion from the piston into rotational motion needed to drive a vehicle.

This transformation of motion occurs during the four-stroke engine cycle: intake, compression, power, and exhaust.

As the pistons move up and down within the cylinder, the crankshaft rotates, turning the engine’s mechanical energy into a rotational force that propels the vehicle.

Types of Crankshafts

There are mainly two types of crankshafts – the flat plane and cross plane.

The flat plane crankshaft, often found in high-performance vehicles, offers the advantage of less rotational inertia, allowing the engine to rev faster. However, they can create more vibrations.

The cross plane crankshaft, commonly found in V8 engines, is known for its smooth operation and better balance but has more rotational inertia.

flat plane vs cross plane crankshaft

Potential Problems and Maintenance

Like any mechanical component, crankshafts are susceptible to various problems.

These include wear and tear from regular use, bending from excessive loads, or complete failure due to poor maintenance or manufacturing defects.

Regular inspections, proper lubrication (in the form of oil), and timely repairs can mitigate these issues and ensure the crankshaft’s long and efficient service life.

What is the most common failure of a crankshaft?

The most common cause of crankshaft failure is fatigue failure. The crankshaft is always subjected to a cyclical load along with bending and shear forces, causing fatigue over time.

What happens when a crankshaft fails?

If the crankshaft fails the engine will most likely cease up and stop running. You’ll likely notice loud banging and knocking sounds along with harsh vibrations.

  • Andy Lewin

    Andy Lewin is a senior mechanic, ASE qualified master technician, and an experienced automotive engineer. He's passionate about serving the automotive community with the highest-quality and trustworthy information on all things automotive. He loves to write about car repairs, maintenance, car modifications and tuning, faults, and much more.

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