• Sat. Jun 22nd, 2024


El crankshaft is one of the key parts of a piston engine. That is, the type of engines used by virtually all motorcycles, cars, vans, trucks, etc.

In this article we will tell you what the crankshaft is, how it works and what parts it has. In addition to its possible breakdowns and some details on its manufacture, dismantling and balancing. That is to say everything necessary to fully understand this part of the engine.

what is the crankshaft

It is a shaft placed in the lower part of the engine composed of several cranks, which are those that receive the movement of the pistons through the connecting rods. This provides the rotational motion needed to move the car or other motorized vehicle.

crankshaft operation

To understand how the crankshaft works, one must know what plays inside a car. It is the part responsible for transforming the vertical movement of the pistons into a circular movement. It can therefore be used to move the wheels in Transmisión.

The comparison that helps the most to understand this is that the crankshaft does the same thing as the pedals of a bicycle. Only, instead of rotating by the action of the legs, it is moved by the explosions produced inside the combustion chambers, which push the pistons downwards with cranks.

At one of its ends, the crankshaft has the flywheel, which is a disk (usually double mass) to which the clutch is coupled and decoupled. Something that we control through clutch pedal, if it is a Manual gearbox or, by itself, if it is an Automatic gearbox.

From there, almost all cars work the same way. The rotational movement passes through the gearbox, which regulates its speed according to the gear engaged.

From there the torsion is transmitted to the transmission shaft (if the motor is on a different axle from the drive wheels), from there to the differential, which allows this turn to be bifurcated into two bearings and turn at different speeds in a curve.

Finally, these rotate the wheels of the car by constant velocity joints. If you want to know in detail how each element works, go to the links inserted throughout the text.

Crankshaft of an engine with connecting rods and pistons

As you can see, a whole chain of rotating components that allow the car to move. Although it all depends on the crankshaft performing its function in the engine: converting vertical motion into rotation.

Therefore, rotary or Wankel engines they do not need a crankshaft, since the combustions generated inside already produce a circular movement.

Parts of a crankshaft

Among its constituent elements, we can note:

the accessories that make a turn on the same box
the crankpins which support the rotation of the connecting rods
arms joining the crankpins and
counterweights that allow no vibration.

The supports must be hardened, like the crankpins, by various heat treatments. A process in which absolute precision is required to achieve the right tolerances to be sustainable. Any failure in this process can cause fatigue cracks.

crankshaft manufacturing

Materials such as wrought iron, which was then is, mechanize there balances.  It is given a very compact shape which gives it great rigidity. Although this increases the possibility of loss or deformation of the material due to friction. However, this is not a problem due to the constant lubrication it receives.

The inside of the crankshaft can be hollow, to reduce weight and save on manufacturing materials. A structure that is used to drive the oil under pressure which keeps it lubricated. The support bearings and the crankpins receive the oil through small holes made in different areas of the crankshaft.

Crankshaft Failure Symptoms

It is very rare for a crankshaft to fail. They are designed in such a way that they last the life of the car to be spared. However, when failures do occur, most come down to these possibilities:

The crankpins They must be perfectly lubricated at all times. Otherwise, they will gradually wear out. This fault can be caused by:

Not having the correct oil level at all times
An oil pump failure that is not fixed in time
Do not change the oil at the time, to the point that its degradation is very great.

These causes will not only deteriorate the crankshaft and its pins. Other parts of the engine will suffer significant damage, usually before the crankshaft itself. For example, him camshaft, cylinders, piston rings or connecting rods.


It’s weird, but the crankshaft can break too. Although if it is not due to a manufacturing defect, the most common is that it is due to abnormal use. circle at low revs and with a lot of load the crankshaft suffers a little more.

But it is not likely to break the crankshaft of a car. In other types of heavy vehicles this may be something plausible. Reprogramming or modifying the engine, in such a way that it gives much more than normal, is also a probable cause.

In our country they are not common due to the limits imposed by the legislation, but in other countries much greater improvements can be observed frequently. For example, he Toyota Yaris GR Powertune 500 hp from Australia.

Of course, if for some reason the crankshaft was out of balance, it can also break easily after a few hundred miles. But it is very rare if the car has all its factory components. In any case, it is more likely about modifications or deep repairs of an engine, in which the calculations to balance it have not been done well.

How to remove the crankshaft

Crankshaft with connecting rod and piston

As you may have seen in the description of the crankshaft, it is attached to the engine because the connecting rods are attached to their crankpins. It is also linked to the transmission via the flywheel.

For this reason, the crankshaft extraction process is very long and complex, and therefore represents a very high invoice in the workshop.

To extract it, it is necessary to remove the chains or belts from the engine. What’s included auxiliary strap and timing belt. Then you need to remove the auxiliary pulley or damper and the crankshaft damper or harmonic balancer.

Next you need to remove the sump to reach the crankshaft through the bottom of the engine and in many cases remove the oil pump. Then it is the turn of the caps of each connecting rod, remove the bearing caps which fix the crankshaft to the engine. When disassembling it, care must be taken because the crankshaft is very heavy.

These are the most common steps to disassemble an engine’s crankshaft, but each model is different. It is also possible that the water pump must be removed in the process, which should empty the refrigeration circuit.

crankshaft balancing

Crankshaft balancing is a process not normally done in conventional cars. However, you have to do deep modifications to the engine, in which some kind of lightening was done to increase power.

This involves reducing or increasing the weight of the engine’s counterweights so that it can run vibration-free. It also balances complex repairs, which are usually not done in normal cars.

This requires specialized equipment that works on the same principle as tire balancers. In other words, we want the mass balance point to always be in the same place throughout the rotational path of each part.

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