Crankshaft overview by mechanic

The information in this article is from an expert mechanic, and it seeks to break down the crankshaft for ordinary folks. Hence, we'll be talking about crankshafts and crankshaft position sensors, their functions, how they work, and why they are important to the overall performance of the vehicle. We tried to avoid industry-specific jargon as much as possible. Enjoy!

 Crankshaft assembly



Vehicles are similar to human bodies in many ways. For instance, the spinal column (or the backbone) acts as the structural center of the human body.  In vehicles, the crankshaft is basically the backbone of the internal combustion (IC) engine. It ensures that the car engine functions properly.

Crankshafts are rotating shafts that translate the linear motions of the pistons into rotational ones in the IC engine. Crankshafts experience high cyclical loading levels as a result, making them prone to wear and fatigue. They should therefore have very high fatigue strength and wear resistance to ensure long service life.

Importance of lubrication to the crankshaft

Lubrication plays a vital role in the general efficiency of any engine. This is especially so because their working mechanism actively involves metals rubbing against one another. To prevent unnecessary stress on the crankshaft, both its main journals and rod journals run on a film of oil.

The film is situated on the surface of the bearings. Here's how the lubrication process works: The engine block supplies oil to the main bearing through the oil galleries. It flows to various crankshaft saddles from there. The corresponding holes in the bearing shell then receive the oil to the journal.

Types of crankshafts

The monolithic and the assembled crankshafts are generally the two main types of crankshafts.

Monolithic crankshafts

Multi-cylinder car engines employ this type of crankshafts.

Assembled crankshafts

Assembled crankshafts are also known as fabricated crankshafts. Different components come together to make them. Mostly found in motorcycles, cars also use it.

Pro tip: The crankshaft type determines the kind of connecting rods used.

Components of a crankshaft

Components of a crankshaft

The main journals, crankpins, crank webs, and counterweights constitute the crankshaft. We'll discuss each one after the other.

Main journals

The main journals perform the function of carrying the main bearings and defining the axis of the shaft rotation.Two types of journals are present on a crankshaft:

  1. The main bearing journals. These form the axis of the crankshaft rotation.
  2. The connecting rod journals. They fasten to the ends of the connecting rods and go up to the pistons


This is the component of the crankshaft that links the connecting rods.

Crank webs

This component connects the crankpins to the main journals.


They connect to the crank webs where they provide balance for the crankshaft. Pro tip: The engine build, bearing numbers, and stroke size determine the design of the crankshaft. And it's ultimately based on the firing ability of the engine and cylinder numbers.

Function of crankshafts

The crankshaft is a moving component of the Internal Combustion (IC) engine. It connects to the piston via the connecting rod and is located within the engine block.

Function of crankshafts

The combustion of the air-fuel mixture (also known as the charge) produces power and pushes the piston straight down the cylinder. The crankshaft functions primarily to convert this vertical motion of the piston into rotational motion. It does it by swinging about and shooting the piston back up the cylinder.

The counterweights help to smoothen the engine revolutions in the process. To put it simply, the crankshaft offers a smoother ride to considerable motors bearing multiple cylinders. The crankshaft functions secondarily to transmit power to other engine parts such as valve timing, oil pump, cooling (water) pump, air conditioning compressor, alternator, to mention only a few.

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Crankshaft materials

Crankshafts are generally made up of cast iron. Modern crankshafts are, however, made of forged steel. It's gotten by heating a block of steel to red hotness, where it's then formed into the desired shape under extremely high pressure. Alloyed heat-treatment steel and nitride steel materials are also used.

How does it work?

The crankshaft workings are quite straightforward.There's a gap (crank radius or the crank throw) between the centers of the main journal and the crankshaft pin. The piston's range of travel is dependent on its measurement as the crankshaft commences rotation.

A flywheel flange supports the rear end of the crankshaft, which extends outside the crankcase. The flange is a precision component that comes attached to the flywheel.

Its considerable weight helps smoother the pulsation of the pistons at every point in time. The crankshaft is mounted on the ring gear of automated drives. It bears the torque converter and translates it to the automatic transmission.

Common crankshaft problems

Problems on a crankshaft are rare, its components are built to be sturdy and long-lasting. Nonetheless, they still tend to fail with time.Common problems include:

Worn journals

This results from insufficient oil pressure that causes the main journal to make direct forceful contact with the bearing surface. This sees a gradual increase in the clearance, thereby worsening the oil pressure.A worn journal can cause severe damage to the engine if it's allowed to persist. Destroyed bearings are usually where it starts.

Fatigue cracks

Fatigue cracks occur when consistent forces on the crankshaft result in fracture. Installing a good fillet radius can prevent this.Pro tip: Magnafluxing is the technique for detecting crankshaft cracks.

Can you repair a crankshaft?

Yes, you can. The repair can range from polishing and bearing replacement to crankshaft pulley repair and canal cleaning. Crankshafts are also brought in for balancing, dressing, and grinding.These repairs, however, involve very tedious processes that definitely require great mechanical know-how. For all intent and purposes, a professional should handle it.

Crankshaft position sensor

A crank position sensor (also known as a crank sensor) is an electronic component used in an internal combustion engine that monitors and measures rotation speed (revolutions per minute–rpm) and the precise position of the engine crankshaft.

The information gotten is what the engine management system (ECU/ems) uses to control the ignition system timing, as well as other engine parameters.

Crankshaft position sensor

In most modern technical literature, CKP is the standard abbreviation for the crankshaft position sensor.

Can it stop a car from starting?

Yes, it can. It can range from difficulty starting the vehicle to not starting at all if the sensor is bad.

Where is it located?

The crank sensor is situated close to the main pulley (harmonic balancer). Other cars have it installed at the transmission bell housing, or in the engine cylinder block.

crankshaft position sensor's location

Crankshaft position sensor failure

The position sensor is in virtually all modern cars running on internal combustion engines. Its failure is often a result of several issues, but two common ones are overheating engine and circuitry problems.

Overheating engine

The excessive build-up of heat in the internal combustion engine can result in damage to the crankshaft sensor. The plastic covering almost always melts.

Circuitry problems

This can range from fluctuating voltage to worn-out and damaged wiring. They can interfere with the correctness of the signals flowing to and from the crankshaft sensor.

Symptoms of a bad sensor

Bad crankshaft position sensor

The following are the typical signs of a bad crankshaft position sensor:

  •     Difficulty in starting the vehicle
  •     Check engine light comes on
  •     Intermittent stalling
  •     Uneven acceleration
  •     Engine misfire
  •     Rough engine idle (vibrating engine)
  •     Poor gas mileage


You know by now the critical role of the crankshaft and how it impacts the general performance of the engine. We also explored in detail the technical importance of the position sensor Always pay attention to the general health of both the crankshaft and its position sensor. Take it to the mechanic as soon as you notice something off. Delay could be disastrous to your vehicle.

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