What Is a Crankshaft,  Functions of a Crankshaft in an Engine?

Crankshaft which is the heart of an engine. The internal combustion process of an engine depends heavily on the crankshaft, which plays a crucial role in converting the linear motion into the rotational motion. The main journal, crankpin, connecting rods, counterweights, and thrust surfaces are just a few of the pieces that cooperate to make sure the engine runs smoothly and effectively.


Complex machines called engines use fuel to produce mechanical energy. The crankshaft plays a crucial role among the many parts that cooperate to complete this modification. The conversion of linear motion into rotational motion occurs in the field of engines, due in large part to the crankshaft. It supports the engine from the inside out to make sure it runs smoothly and effectively. This can help in Engine maintenance. This article will examine the specifics of a crankshaft and its main function in an engine.

What is a Crankshaft?

The internal combustion process of an engine depends heavily on the crankshaft. It enables the production of power by connecting the pistons to the drivetrain. An engine’s crankshaft plays a crucial role in its operation. It is normally constructed of high-strength steel and has multiple carefully engineered parts that work together to ensure the engine runs smoothly.

Crankshaft Materials

Cast iron or high-strength alloy steel are frequently used to make crankshafts. The engine’s power output, weight restrictions, and cost concerns are only a few of the variables that influence the material selection. Because of their higher strength and longevity, forged steel crankshafts are frequently utilized in high-performance engines.

Parts of a Crankshaft:

Main Journal : The center portion of the crankshaft that attaches to the engine block is called the main journal. It transmits power to the flywheel, or flexplate, as it rotates inside the engine block and is supported by bearings.

Crankpin: The parts of the crankshaft that attach to the connecting rods are known as crankpins. They translate the pistons’ linear action into rotating motion, and they are offset from the main journal.

Connecting Rods: The pistons and the crankshaft’s crankpins are joined by connecting rods. They are essential in converting the pistons’ reciprocating action to the crankshaft’s spinning motion.

Counterweights: On the crankshaft, counterweights are carefully positioned to balance the rotational forces generated by the reciprocating motion of the pistons and connecting rods.

Thrust Surfaces: The crankshaft has thrust surfaces that restrict axial movement. They restrict the crankshaft’s excessive forward or backward movement when the engine is running.

Working Principle of a Crankshaft

  • Reciprocating Motion

The fundamental idea behind a crankshaft is to transform the pistons’ reciprocating action into rotating motion. The connecting rods push and pull on the crankpins as the pistons rise and fall inside the cylinders. The pistons’ linear motion is converted into rotational motion by this action, which also rotates the crankshaft.

  • Rotational Motion

The crankshaft’s rotational motion is important for driving a number of engine parts, including the camshaft, water pump, and alternator. Each cylinder fires at the appropriate time throughout the engine’s combustion cycle because the crankshaft’s rotation is coordinated with the combustion order.

  • Firing Order

The cylinders in a multi-cylinder engine fire in a specified order, which is referred to as the firing order. It is chosen in accordance with the engine design and is essential for preserving smooth engine running. The firing order is greatly influenced by the design of the crankshaft and the placement of the crankpins.

  • Engine Balance

A well-performing engine requires careful attention to engine balance. To reduce vibrations and guarantee smooth performance, the crankshaft and its counterweights are properly balanced. Reduced wear and tear, increased fuel efficiency, and higher overall performance are all benefits of proper engine balance.

The Functions of the Crankshaft

The crankshaft’s main function is to change the pistons’ reciprocating action into rotary motion. The connecting rods are compelled when the pistons travel up and down in the cylinders, and the connecting rods then transfer that force to the crankshaft through the crankpins. The gearing system receives power from the crankshaft’s revolution and uses it to drive the car’s wheels.

Primary Function

Conversion of Linear to Rotational Motion :

A crankshaft’s essential role is to transform the pistons’ linear motion into rotational motion. The connecting rods linked to the crankpins transmit the reciprocating motion to the crankshaft when the pistons rise and fall inside the cylinders. The crankshaft’s offset crank throws make sure the linear action is converted to a circular motion.

Secondary Functions of a Crankshaft

Balancing and Vibration Dampening

In addition to converting motion, the crankshaft is a key element in keeping the engine balanced. In order to balance out the weight of the pistons and connecting rods and keep the engine operating smoothly, the crankshaft has counterweights.

Distributing rotational force

The oil pump, camshaft, and other parts of the engine receive the rotational force produced by the pistons via the crankshaft. This enables the engines to run in sync with one another and makes sure that power is effectively distributed throughout the system.

Connecting a rod attachment

Connecting rod attachment points are provided by the crankpins on the crankshaft. The reliable transfer of power from the pistons to the drivetrain depends on the tight fit between the crankshaft and connecting rods.

Signs of a Failing Crankshaft

For quick repairs, recognizing the symptoms of a problem crankshaft is essential. Excessive engine vibration, knocking noises, poor engine performance, and oil leaks are a few typical warning signs. It is advised to get the crankshaft evaluated by a skilled mechanic if any of these symptoms are present in order to prevent additional damage.

Common Issues and Maintenance

Crankshafts are at risk of wear and damage over time, just like any mechanical component. The most frequent problems that can occur are fatigue failures, crankshaft bending, and journal wear. For the crankshaft to last a long time and to perform at its best, regular maintenance is necessary, including oil changes and checking the bearing clearances.

Importance of a Well-Designed Crankshaft

A well-designed crankshaft is essential for an engine to run smoothly and effectively. Its careful engineering guarantees optimal balancing, lowers vibrations, and puts less strain on engine parts. A superior crankshaft improves the durability, fuel economy, and overall performance of the engine.

Advancements in Crankshaft Technology
Innovative crankshaft designs and materials have come into being as a result of the ongoing improvements in automotive engineering. The power-to-weight ratio of crankshafts, for instance, has improved with the development of lightweight materials like carbon fiber-reinforced composites, improving total engine performance and fuel efficiency.


In summary, the crankshaft is an essential part of an engine’s operation since it converts linear action into rotating motion. The main journal, crankpin, connecting rods, counterweights, and thrust surfaces are just a few of the pieces that cooperate to make sure the engine runs smoothly and effectively. We can guarantee dependable and smooth engine operation by maintaining the crankshaft’s strength through routine maintenance and taking care of any problems as soon as they arise.


Q1. Is it true that all crankshafts are the same size?

No, the size and design of crankshafts vary based on the engine’s configuration, displacement, and required power output.
Q2. Can the performance of an engine be improved by a lighter crankshaft?

A lighter crankshaft does indeed lower rotational inertia, allowing the engine to rev more easily and perhaps enhancing overall performance.
Q3. What do counterweights in a crankshaft serve for?
Counterweights reduce vibrations and promote smooth engine performance by balancing the rotating forces produced by the pistons’ and connecting rods’ reciprocating motion.

Q4. Can a crankshaft that is damaged be fixed?
While minor faults can frequently be fixed using reconditioning methods, significant damage can require replacing the crankshaft.
Q5. Are there types of crankshafts available?
Yes, there are various types of crankshafts, such as cross plane and flat-plane crankshafts, as well as some unique designs for particular engine designs.

Q6. How long does a crankshaft last?
A crankshaft’s lifespan is influenced by a number of variables, such as the type of engine, the operating environment, and maintenance procedures. A crankshaft can last for many years with the right upkeep and care.