Absolutely any engine is a rather complicated mechanism, which consists of many different components. Every detail of this mechanism ensures the smooth and correct operation of the entire system as a whole. At the same time, some details in a large mechanism can play serious roles, while others are not so functional. The crankshaft, like other components and parts that are directly related to it, is the most significant part of the internal combustion engine. It is he who provides the rotation of the flywheel by converting the combustion energy of the fuel mixture into mechanical work.
One of the important details in the engine design is the main bearing. This is a small part in the form of a half ring made of medium hard metal with a special anti-friction coating. When the engine has been used for a long time, these bearings or liners undergo severe wear. The article will take a closer look at these small, but very important elements of the internal combustion engine.
general description
The main bearing of the engine or the liner is nothing more than a plain bearing, providing the possibility of rotation of the crankshaft. The rotation process takes place as a result of the combustion of the fuel mixture in the combustion chamber. During active operation of the engine, the parts experience friction - increased loads, as well as a high speed mode, can damage the motor. To prevent this situation and minimize the degree of friction, the main significant elements are coated with a thin layer of lubricant - in this case, engine oil. The main bearings of the crankshaft are lubricated by means of a standard lubrication system. In this case, an oil film is formed only under the influence of high oil pressure. On the working surface of the liners there are holes, as well as annular grooves for supplying lubricating fluid to the necks of the crankshaft.
Appointment
In engines of any design and any type, crankshafts are constantly subject to enormous loads - physical and thermal. During engine operation, the main bearing holds the crankshaft on the axis. The operation of the crank mechanism is supported and provided only by these inserts. The crankshaft journals are presented in the form of inner cages, and the main bearings are external. These parts, as already noted, are lubricated through oil channels.
Device in detail
So, a thin-walled liner is a steel tape curved into a half-ring shape. A special anti-friction layer is applied to the working surface of the part. These are tin-aluminum alloys. In engines with increased loads, lead bronze is used as an antifriction coating.
Materials
The main bearing is made of several layers. The first layer is predominantly copper - the percentage of copper is from 69 to 75 percent. The second is made from lead - it is contained in an amount of 21 to 25 percent. As the third layer, tin is used - not more than 4 percent.
Dimensions
The thickness of the main bearing shell is about 1.5-2 millimeters. It should be noted that sometimes a different composition can be used as materials for the production of this part - instead of copper and lead-tin alloys, special alloys based on aluminum are used.
But there is no standardization of materials for the manufacture of these products - each manufacturer makes an insert according to its unique formulas. The only thing that unites products among themselves is a steel tape.
Practice shows that the following layer sizes are used in the production of plain bearings. So, the thickness of the steel base is from 0.9 mm or more. The base layer has a thickness of up to 0.75 mm. Nickel layer is 0.001. The tin and lead alloy layer is 0.02-0.04 mm. The tin layer is 0.005.
Any alloys used in the production are individually selected for each motor and are calculated taking into account the hardness of the materials from which the crankshaft is made. To increase the resource and performance of new or repair motors, it is recommended to use only those parts that are recommended by the manufacturer.
The thinner the main bearing, the higher its characteristics. Thinner products lie much better on the bed, have better heat dissipation, the gaps in them are lower. In modern motors, manufacturers try to use thinner plain bearings.
The liner must be made not only of correctly selected components. Form is also very important. The fact is that for proper installation it is necessary that the bearing has an interference fit on the diameter of the crankshaft bed.
Preload is done not only by the diameter of the product, but also by its length. In this way, excellent contact between the bearing shell and the bed is achieved. For shafts with a diameter of up to 40 millimeters, the interference must be between 0.03 and 0.05 millimeters. For larger shafts (70 millimeters) and above, the interference is between 0.06 and 0.08 millimeters.
The device of this part also has an upper part - these are the covers of the main bearings. They are fixed with bolts or studs on the crankcase.
This part is produced, namely the liner, by stamping from steel tape. The stamp gives the details a form. And then the end parts and the working surface are processed. This part is very accurate. Tolerance from nominal size to 0.02 millimeters in length and up to 0.005 in thickness.
Groove and its features
So that lubricant is constantly supplied to the part, a groove is cut through the entire length of the crankshaft main bearing - its width is 3.0-4.5 millimeters, and its depth is up to 1.2. On engines of an old design, this groove was made on the liner and on its cover. In modern motors, the bottom liner does not have a groove. If there is still a groove, then it has a reduced maximum load.
Failure to cut the groove leads to the fact that the level of maximum loads increases significantly. This reduces the bearing area.
Castle
Often, when stamping these parts, a lock is made on it. The device of the main bearings provides a lock near the middle. To keep the castle strong, it is made without breaks.
According to the traditions of designing internal combustion engines, locks are located depending on which side the crankshaft rotates. On the root liner, it is needed more for alignment during its installation and for safety against turning. When the engine experiences oil starvation, the bearing heats up intensely, and then no locks will save it - the liner rotates.
Main types
Liners are made for each type of engine. However, they vary in inner diameter. Depending on the motor model, the diameter of the liners will be different even for one specific motor. The step size is 0.25 mm. Size range - 0.25 mm, 0.5 mm, 0.75 mm and beyond.
These or other types of bearings are selected according to the condition in which the crankshaft journals are located. Over time, due to natural wear and tear, the necks collapse. To compensate for this wear, manufacturers produce the so-called repair main bearings. To fit the neck of the crankshaft for one or another bearing, the shaft is ground to the next size.
Check and Replace
Since the crankshaft operates in severe conditions under the influence of high temperature and other loads, only these bearings can hold it on its axis. The necks serve as the inner cage, and the liners - the outer. Like other engine elements, these parts also need to be periodically changed.
Change the liners more often due to wear and tear, as well as due to rotation. You can crank the liner for the following reasons. This is a viscous oil, ingress of abrasive oil, a small tightness when installing the cover, insufficient viscosity of the lubricant, operation under overload conditions.
Signs of a need for replacement
To determine the need to replace the main bearings, it will be necessary to take measurements with a micrometer. But often it is possible to identify the breakdown visually. If the liners are rotated, then removal and installation of new ones instead of them should be carried out very quickly. You can understand whether a replacement is necessary by the loud knock of the shaft, the decrease in power, or the attempts of the motor to stall.
Conclusion
So, we found out what the main bearing is. As you can see, this is a very important element in the crank mechanism. The health of the entire engine of the car depends on its condition. Therefore, the bearing should be as reliable as possible and have a high service life.