A Car's crank shaft

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Function, structure, and symptoms of malfunction

The crankshaft is a particularly important part of your combustion engine. Although it is very robust nowadays, damage to it can still occur. Primarily, it is its high load, since this makes sure that the impact movements of the engine pistons are converted into the necessary rotary movement for your vehicle drive. Extremely high forces are at work here and this component has a complex structure. It’s not hard to imagine that a defect in this part often is the cause of very expensive repair costs. In order to keep this from happening in the first place, we will go into depth about the function of the crankshaft and how you can make sure that it works without problems for as long as possible. Should problems still come up, it is essential to intervene as soon as you can in order to avoid even greater damage.

function and structure

 

Engine crankshaft serves to generate a rotary motion or torque from the up and down movements of the pistons. This is done in conjunction with the corresponding connecting rods, which also connect the pistons to the crankshaft. Another important component is the flywheel. The high load on the above-mentioned parts is caused in particular by the constant and, what is more, very abrupt changes in the direction of movement. This not only causes torsional vibrations, but also exposes the shaft and the corresponding bearings to torsional and bending forces.

Because of the way they work, crankshafts are made of an especially tough inner core and materials with very hard surfaces. This is also the reason why most crankshafts are still forged.The raw material used for this is a so-called nitriding steel or a specially alloyed tempering steel. In addition, parts that are not subject to particular stress, such as the bearing journals, also have a surface hardening. The basic components of a crankshaft are crankpins, crank webs, journal bearings, and corresponding counterweights. The corresponding main bearings accommodate the shaft journals, so that the axis of the rotary movement is also determined by these. The crank pins, on the other hand, are used to connect the connecting rods. The crank webs in turn provide the connection between the two types of journals mentioned. To ensure that the rotary movement is as smooth as possible and that no imbalances occur, the counterweights are also connected to the crank webs. However, the precise crankshaft design depends on the exact engine type. The number of cylinders, stroke length, engine design, and engine firing order determine the composition. The movement of the crankshaft is monitored by the crankshaft sensor. The crankshaft gear is a component that is responsible for torque distribution in the vehicle. For example, it drives the oil pump and the intake and exhaust valves of your engine. This component is not one of thecar engine parts components that must always be replaced after a certain period of time. On the contrary, the crankshaft sprocket is only replaced in the event of problems or a defect.

What causes crankshaft damage and symptoms of a defective one.

If your crankshaft is defective, you will recognise this by various symptoms. Several often appear at the same time. Some of these can also be recognised as early warning signs, while others only appear when there has been severe damage to the crankshaft. Some of these are not always specific to crankshaft bearing damage or similar defects, but can also occur with other problems. In this case, we recommend that you proceed using the process of elimination and gradually rule out all possible sources of error. Basically, an incorrect, i.e. too large or too small, axial play of the crankshaft plays an important role regarding problems with this component.

With modern engines, serious damage to the crankshaft isn’t common because these components can now withstand even more extreme loads. Nevertheless, engine damage can still happen if there is a lack of engine oil or if the engine speed is much too high. Whereas a clearly too high speed is actually reliably prevented by the engine electronics. However, an error when changing gears can definitely cause the crankshaft to break. Imagine that you are driving at high speed in third gear and now want to shift into fourth gear; Now you catch second gear instead – with a bit of bad luck you have now caused very serious damage to your engine.

Here is a much more common cause: a lack of engine oil. Sooner or later, this can not only cause not crankshaft bearing damage, but the connecting rod bearings will be affected. If there is no oil left at all, the dry friction usually takes its full toll after 10-15 minutes, if not sooner. Since a turbocharger, which is often present in modern vehicles, is usually even more sensitive (after 10 minutes without oil, much damage has already been done), the crankshaft is usually not so badly affected. You can usually recognise crankshaft damage by the typical noise it makes. If you hear a clacking sound that matches the engine speed, this commonly indicates a defect in the connecting rod bearings. If you can hear a rumbling or grumbling coming from deep within your engine, the crankshaft bearings have been  affected. Do not continue to drive and turn off your engine right away if you notice this type of symptom so that you can avoid even more serious damage.

Crankshaft repair and costs

Of course, every home mechanic is “happy” to remove a crankshaft and grind the affected bearing points to undersize. They then have to check the hardness of the bearing journals and may have to subject them to heat treatment, because bearings that are too soft would wear out quickly. After heat treatment, the concentricity must be checked; most shafts must not deviate more than a hundredth of a millimetre, because they could have warped during hardening. The straightening of a crankshaft is a demanding task and requires real specialists; there is no machine for this. After that, everything has to be reassembled with oversize bearings – and now you’re done. Or in short: it's really not worth it. For a standard four-cylinder, it is cheaper to either get a good used replacement engine from a trusted recycler. It does not necessarily have to come from the manufacturer, the independent aftermarket also offers quality refurbished engines.

Summary

The crankshaft is one of the most stressed engine parts of all. The bearing shells of the crankshaft can wear out quite easily. Nevertheless, this engine component is low-maintenance and only needs to be replaced or repaired when a problem occurs. In most cases, it is then essential to take apart the engine, so that the repair costs rise very quickly. It is best to ask your specialist workshop for their advice on how economical an engine repair would be in this case.

Even today, there are still specialists or specialist companies that carry out the grinding of crankshafts. This is a special form of repair that can partially restore the engine's running smoothness. However, for such a procedure to be successful at all, extremely precise measurement and machining of this sensitive engine component are necessary. Moreover, this form of repair can only be used for minor component damage, so you should always pay attention to symptoms we mentioned so that it won't be too late in the end and much greater damage occurs.