The crankshaft is one of the central components of the combustion engine. However, this component is not readily visible in a car engine. In our article, you will learn everything about the structure and function of the crankshaft in the combustion engine.

Structure and function of the crankshaft

A crankshaft in the engine transmits the force generated during combustion and acting on the pistons. At the same time, the shaft converts the linear movement of the pistons into a rotary movement. For this purpose, each piston in the engine is connected to the crankshaft via a connecting rod. The crankshaft transmits the rotary motion to the clutch via the flywheel. From here, the power is transmitted to the gearbox. The rotary motion is then transmitted to the wheels of the car. In addition to the flywheel, the crankshaft also drives the belt drive for the auxiliary units and the camshaft.

Components of crankshafts

A crankshaft is made up of several components. This also applies if the shaft was forged in one piece and does not consist of individual parts. This type of construction is common in today’s car engines in order to better absorb the occurring torque. In most cases, the crankshaft is made of alloyed steel, which is hardened and partially polished.

• Shaft journals: The shaft journals form the axis of rotation of the crankshaft. The crankshaft is rotatably mounted in the engine block at these points. Crankshaft bearings reduce friction.
• Crankpin: The crankshaft is connected to the individual connecting rods via the crankpin or connecting rod journals. During operation, this part forms a circular path around the axis of the crankshaft.
• Crank webs: Each crankshaft crank is made up of two crank webs. These parts of the crankshaft act as crank arms between the crank and shaft journals.
• Counterweights: Counterweights integrated into the crankshaft ensure that the engine runs smoothly and rotates evenly. The weights are located opposite the crank pins.

Different crankshafts depending on the engine

The design and function of the crankshaft differ depending on the engine type. The arrangement and number of cranks and bearing points vary according to the number of cylinders. The crankshafts are designed differently depending on the force and torque applied. The material and design of the crankshaft can also vary.

The function of the crankshaft in combustion engines

The energy released during the combustion of fuel and air sets the piston in the cylinder in motion. This force is transmitted to the crankshaft via the connecting rod. The engine piston and connecting rod move in the direction of the crankshaft. The design of the crankshaft ensures that the linear movements occurring are transmitted as torque. At the same time, the crankshaft ensures that the piston moves in the direction of the cylinder after bottom dead centre has been exceeded. As the piston is pushed back, it compresses the mixture required for combustion or expels the combustion exhaust gases. In engines with several cylinders, the specific design of the crankshaft ultimately determines the firing order of the engine.

Defects in the crankshaft

A defect in the crankshaft occurs rather rarely and can have various causes. Diagnosing a crankshaft defect is not always easy. After removing the oil pan, the condition and function of the crankshaft can be checked. Sometimes it is not the crankshaft itself that is defective, but one or more of the installed crankshaft bearings.

Causes of crankshaft defects

The crankshafts of modern car engines are designed to be robust and durable. Nevertheless, crankshaft wear can occur in engines with high mileage. A common cause of defects is the inadequate lubrication of crankshafts. Excessive engine speed rarely occurs in modern engines, but can also damage the crankshaft.

Typical symptoms of a defective crankshaft

The symptoms of a defective crankshaft can be varied. There are often banging or rumbling noises when the engine is running. Rattling or knocking noises, for example when accelerating, also occur from time to time. In addition, unusually strong vibrations or generally uneven engine running may indicate defective crankshafts.

Repair and replacement of defective crankshafts

Replacing or repairing a crankshaft usually involves a great deal of work. As a rule, the engine must be removed from the car in order to dismantle the shaft. All bearing points on the engine block and the connecting rod bearings on the crankshaft must then be loosened. The same applies to the connections to the flywheel, belt drive and valve train.

Having the crankshaft repaired

In principle, it is possible to repair a defective crankshaft. Specialist companies often overhaul crankshafts as part of an engine overhaul. It is possible to balance or grind the crankshaft removed from the engine. Beforehand, the shaft is thoroughly checked for damage and measured. The crankshaft is then machined, which is usually a complex process.

Repairing the crankshaft or replacing the engine

Repairing an engine is always possible, but does not always seem economical. Especially with older vehicles, the repair costs sometimes exceed the value of the vehicle. In this case, it may be worth replacing the entire engine with a used engine.