The crankshaft is one of the main elements of the engine. It is part of the crank mechanism. It has a complex device. What is this mechanism? Let's take a look.
Design and purpose
The crankshaft takes the forces from the piston and converts them into mechanical energy. Rotational forces act on this mechanism. It works constantly under high load. Therefore, so that the part does not fail prematurely, crankshafts are made of high-quality, high-strength cast iron alloys. Then all parts are hardened by high frequency current. There are shafts with a double counterweight or no counterweight at all. The crank shaft is located directly in the motor housing. As for the design, it generally depends on the engine.
Despite some differences, the designs have a lot in common. The crankshaft is a complex of several parts. Main journals are used as a support for this design - models with four necks are more common, but there are also three-bearing ones. Shafts are installed in six-cylinder engines, where there are 7 such supports. In order for the crankshaft to be balanced,counterweights are used. If the cylinders have a small diameter, then single counterweights are used. Due to these parts, the smoothest operation of the power unit is ensured.
So, knowing what the engine crankshaft is designed for and what forces act on it during operation, you can understand why the interfaces between the cheeks and the connecting rod journals are slightly rounded. This prevents premature failure.
There is a connecting rod between the cheeks. Mechanics who service engines call it "knee". It is designed to ensure uniform ignition, so that the operation of the engine is as balanced as possible, so that minimal torsional and bending forces act on the shaft. The crankshaft is a part that operates at high speeds. The rotation of the connecting rods and the shaft itself on the supports is provided by plain bearings. Thrust elements are installed on the extreme or middle root neck. The purpose of this bearing is to prevent axial movement and move the mechanism.
If you consider how many parts must work smoothly and accurately in one mechanism, it is easy to say that the crankshaft is carefully balanced during the production process. But sometimes it is possible to detect unbalanced details. These products are not available for sale.
Crankshaft inside operation
The principle of operation is generally simple. When the piston is as far away as possible, the cheeks and connecting rod of the crankshaftline up in one line. At this moment, fuel ignites in the combustion chambers and gases are released that move the piston to the crankshaft. The connecting rod moves with the piston, the head of which turns the crankshaft. When the latter turns, the connecting rod neck moves up and the piston moves with it.
Lubrication plays an important role. The crankshaft is a rotating part, which means it will experience friction.
From the common lubrication line to the journal bearings, a supply of lubricant is provided. Then, through the channels in the cheeks, the oil will also get to the necks of the connecting rods. Lubrication significantly increases the wear resistance of all shaft parts.
Due to high loads, this mechanism fails. Among typical malfunctions, accelerated wear of the necks can be distinguished. It is associated with problems in the cylinder block. It is also not uncommon to experience scuffing on the surfaces of the necks.
This happens due to poor circulation or lack of lubrication, or due to temperature violations. Scratches on the surfaces of the necks can be seen especially often. It is necessary to distinguish between just scratches and cracks that are formed due to metal fatigue. Often there are beats and deflection of the part. This is especially true for high-revving car engines.
Another typical malfunction is the deviation of the necks from their factory size. But this is a more natural process than all the others. It must be taken into account that the dimensionscrankshafts have a tolerance of no more than 0.02 millimeters. Any discrepancy is eliminated by turning on specialized equipment.
How do I replace?
Of course, for some types of malfunctions, you can get by with repairs - grinding or turning. But sometimes the shaft cannot be restored. In this case, you can replace the old mechanism with a new one. By the way, in the engine it is the most expensive component. Especially in diesel powertrains.
Before the crankshaft is replaced, the end play is checked. This will simplify the selection of axial bearings. It is necessary to find marks on the liner and cylinder block. They indicate the installation direction of the main bearing caps. All parts that interfere with the dismantling of the shaft must also be removed. Repair manuals describe the dismantling process in different ways, as there are 8 and 16-valve engines, with in-line or V-shaped cylinder arrangement. Then you need to install a new crankshaft in place of the old one - you must strictly follow the instructions of the car manufacturer and do not confuse the position of the crankshaft. Due to the high responsibility, all work must be carried out in a specialized service.
So, we found out the device, purpose and principle of operation of the car crankshaft.