Crankshaft: without which the engine is not the engine

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The engine has no “main” and “not main” details – all the details are equally important and breakage of any of them influences performance of the power unit. But there is one detail that makes an engine of an engine – this is a crankshaft that converts the reciprocating motion of the pistons and connecting rods into rotational motion. Read about the crankshaft, its structure and role in the engine in our article.

One of the most serious problems of technique is the conversion of reciprocating motion into rotational motion, and vice versa. This problem was solved 2.5 thousand years ago, and the solution created then has remained practically unchanged to this day. This is a crank.

In modern internal combustion engines, it is also necessary to convert the reciprocating motion of the pistons and connecting rods into the rotational movement of the shaft, flywheel and, ultimately, the wheels. The same crank, or rather the crank mechanism, the main part of which is the crankshaft, copes with this task.

If the engine “knocks” – this is a possible sign of failure of the crankshaft. When the necks are worn out or there are serious cracks on the detail, a replacement is necessary. Otherwise, you may need a major overhaul of the power unit or the purchase of a new one, which is not cheap.

How crankshaft works

The crankshaft has a rather simple structure: it consists of knees containing the main and rod necks, separated by cheeks. The main necks are the axis of the crankshaft, so they pass exactly along its center. The connecting rod journals, as the name implies, are used for clamping and receiving forces from the connecting rods. As the crankshaft is a crank, the connecting rod journals are removed relative to the axis of the shaft and are held by cheeks.
The number of conrod lathes is equal to the number of cylinders, however, in most V-engines, two cylinders lean on one neck at once. On the other hand, on modern V- engines, crankshafts can be found in which there is one neck for each connecting rod, but the twin necks are shifted 18 degrees to each other. The root necks have a larger diameter than the connecting rods.

Cheeks perform several functions. They do not only connect the necks in a single construction, but also play the role of counterweights to balance the connecting rod necks and connecting rods. The absence of counterweights can cause significant vibrations, which in high-speed engines can lead to destruction of the engine.

Вал коленчатый

The greatest loads on the crankshaft are at the joints of the necks and cheeks, therefore, to evenly distribute the loads on these sections, they are performed by the fillet, that is, the transition from the neck to the cheek is made with a radius of rounding.

Generally, the position of the necks and cheeks in the crankshaft should ensure the most efficient conversion of the reciprocating motion into rotational motion, prevent the occurrence of vibration and hesitation, balance the engine and, finally, reliably withstand bending loads.

Full-support and not full-support crankshafts

The main crankshaft journals serve not only as an axis, but also as a support for the entire crank mechanism. Loads from the crankshaft are transferred to the engine through the main journals, which are supported by the main bearings embedded in the crankcase.

There are two types of crankshafts that differ from each other with the type of support:

– Full-support. In such shafts, there are more root necks than connecting rods, while the root necks are located on both sides of the connecting rod necks, alternating with them (and there are one more root necks than the connecting rods);

– Not full-support. In such shafts, the main necks are smaller than the connecting rods, while on both sides of the cheek there can be two crank pins displaced by a certain angle.

Not full-support crankshafts have a simpler design, however, due to the smaller number of support points on the engine crankcase, they must be more rigid and durable, and therefore heavier. Therefore, today, full-support crankshafts, which with more complex production are more light and reliable, are more common.



The crankshaft is supported by plain bearings (also called liners) embedded in the crankcase. Bearings are also provided for the support of the connecting rods on the crankshaft. These bearings are made of steel tape covered with a special anti-friction alloy, which reduces friction between the bearing and the shaft.

Lubrication of the crankshaft and crank mechanism parts

A special issue is the lubrication of parts of the crankshaft and the whole crank mechanism. This question is really very important as plain bearings are used to support the main journals on the crankcase and the connecting rods on the crank pins, which can work normally only with constant lubrication.

Коленчатый вал

Channels are provided for supplying oil to the rubbing parts and parts inside the crankshaft in all its necks and cheeks. And to ensure reliable oil flow to the bearings, its supply is carried out under pressure.

Interaction of crankshaft with other details

As it was said above, the crankshaft takes the load from the connecting rods, converting them into the torque. The torque is transmitted through the shank (back shaft output) to the flywheel and then to the transmission. The torque is transmitted to the camshaft and auxiliary engine systems through another part of the shaft (front) or toe.

The torsional balancer is also often mounted on the toe – a simple device of two disks connected through springs, rubber gasket, silicone fluid or other elastic material. The balancer minimizes torsional vibrations of the shaft that occur during engine operation, reducing the risk of damage to the shaft.

The Production of Crankshafts

During its operation the crankshaft experiences heavy loads, so this part is produced whole even for powerful diesel engines. Combined crankshafts have failed in high-speed engines, and now they are practically not used in automobile engines. For the manufacture of shafts, steel or cast iron is used. Cast iron crankshafts are made by casting, cast iron shafts are forged or stamped. In the future, both types of crankshafts are exposed to various kinds of machining to achieve the necessary parameters – the cleanliness of the necks surface, balancing, etc.

Where can you order a reliable crankshaft?

AgroBelContract, Ltd. company is the official distributor of GENMOT in the Republic of Belarus. We offer you only original crankshafts from the European manufacturer. You can check the models available on stock as well as look through the models available for order in our catalogue.

68 thoughts on “Crankshaft: without which the engine is not the engine”

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