The engine crankshaft: what it is, how it works, parts, breakdowns and manufacturing

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

In this article we are going to tell you what the crankshaft is, how it works and what parts it has. In addition to its possible breakdowns and some details about its manufacture, disassembly and balancing. That is, everything necessary to understand this part of the engine well.

what is the crankshaft

It is a shaft placed in the lower part of the engine made up of several cranks, which are the ones that receive the movement of the pistons through the connecting rods. This provides the rotary motion necessary to move the car or other motorized vehicle.

crankshaft operation

To understand how the crankshaft works, you have to know what role plays inside a car. It is the piece in charge of transform vertical movement of the pistons in a circular motion. So it can be used to move the wheels by transmission.

The comparison that helps the most to understand this is that the crankshaft does the same thing as the pedals on a bicycle. Only, instead of turning by the action of the legs, it is moved by the explosions produced within the combustion chambers, which push the pistons down along with Rods.

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

From here, almost all cars work the same. The turning movement passes through the gearbox, which regulates its speed depending on the gear engaged. From there, the twist is transmitted to the transmission shaft (if the engine is on a different axle than the drive wheels), from there to differential, which allows to bifurcate that turn in two bearings and rotate at different speeds in a curve. Lastly, these spin the wheels of the car through CV joints. If you want to know in detail how each element works, go to the links inserted throughout the text.

As you can see, a whole chain of rotating components that allow the car to move. Although everything depends on the crankshaft fulfilling its function in the engine: convert vertical motion to rotary. Therefore, rotary or Wankel engines they do not need a crankshaft, because the combustions that are generated inside them already produce a circular movement.

Parts of a crankshaft

Among its constituent parts can be noted:

that props that make a turn on the same casing
the crankpins that support the turning of the connecting rods
that arms that join the crankpins and
that counterweights that allow no vibrations.

Supports must be hardened, like the crank pins, by various heat treatments. A process in which absolute precision is required to achieve the right tolerances to be durable. Any failure in this process can cause fatigue cracks.

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crankshaft manufacturing

Materials such as forged steel, which was subsequently treats, mechanize y balances.

It is given a very compact shape so that it has great rigidity. Although this increases the possibility of losses or deformation of the material due to friction. However, this is not a problem because of 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 pressurized oil that keeps it lubricated. The bearings of the supports and the crankpins receive the oil through small holes made in various areas of the crankshaft.

Symptoms of crankshaft failure

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

Wear

All the crankpins They must be perfectly lubricated at all times. If not they will wear out little by little. This fault can be caused by:

Not having the proper 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 crankpins. Other parts of the engine will suffer to major damage, usually before the crankshaft itself. For example, him camshaft, cylinders, piston rings or the connecting rods.

Break

It's weird, but the crankshaft too can break. Although if it is not due to a manufacturing defect, the most common is that it is due to a abnormal use. circle to low revs and with a lot of load it makes the crankshaft suffer a little more. But this isn't likely to break a car's crankshaft. In other types of heavy vehicles it may be something plausible.

Reprogram or modify the engine, in such a way that it yields 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 enhancements can be seen frequently. For example, him Toyota Yaris GR Powertune 500 hp from Australia.

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

How to remove the crankshaft

As you 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 bill in the workshop.

To extract it you have to remove the chains or belts from the engine. What includes the auxiliary strap and Timing belt. Then you have to remove the auxiliary pulley or damper and the crankshaft damper or harmonic balancer.

Then you have to remove the sump to reach the crankshaft from the bottom of the engine and, in many cases, remove the oil pump. Then it's the turn of the caps of each connecting rod, remove the bearing caps that secure the crankshaft to the engine. When it is removed, care must be taken because the crankshaft is very heavy.

These are the most common steps to disassemble the crankshaft of an engine, but each model is different. It is also possible that the water pump will have to be removed in the process, which would have to empty the cooling circuit.

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how it balances

Balancing the crankshaft is a process that normally not to be done in conventional cars. However, you do have to do it deep engine modifications, in which some type of lightening has been done to increase power. It is about reducing or increasing the weight of the engine counterweights so that it can rotate without vibrations. It also balances complex repairs, which are not usually undertaken in normal cars.

For this it is required specialized material that works thanks to the same principle as the balancing machines of the tires. In other words, what is intended is that the balance point of the masses is always in the same place throughout the rotation path of each part.

Images – Kojach, Jan Willem Broekema, Brian Burger, Photodesaster, Dvortygirl, Kevin Rheese, OK Foundry Company, Inc., Abilene Machine

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