However, there are bearings there. And not just any, but very specific ones. They are durable, but not eternal, and when they fail, you cannot do without understanding the essence of the matter. Well, for professional repairmen this is simply an ordinary matter.
How does a bearing work?
In modern automobile engines, the crankshafts and camshafts are supported almost exclusively by plain bearings. Rolling bearings (ball, roller, needle) they are used for such purposes only in small motorcycle engines.
The required performance of plain bearings is achieved by using the so-called oil wedge effect. When the smooth shaft rotates, oil is supplied into the gap between the shaft and the hole. Since the load acting on the shaft causes its eccentric displacement, the oil is drawn into the narrowing part of the gap and forms an oil wedge that prevents the shaft from coming into contact with the walls of the hole. The greater the pressure and viscosity of the oil in the gap, the greater the load (before the surfaces touch) withstands plain bearing.
The actual oil pressure in the wedge zone reaches 50-80 MPa (500-800 kg/cm²), and in some designs even more. This is hundreds of times higher than in the feed system. However, one should not think that the feed pressure has little effect on the operation of the bearing. The larger it is, the more intensively the oil is pumped through the bearing and the better its cooling.
Under certain conditions, low friction operation mode (it is also called liquid) may be violated. This happens when the viscosity of the oil decreases (for example, due to its overheating due to insufficient supply) and a decrease in rotation speed as the load increases.
Often, especially after engine repairs, the non-optimal geometry of the unit also plays a role. With a slight deviation of the shape of the surfaces from the cylindrical, with a skew of the axes and other defects of the parts, a local increase in the specific load is possible (that is, the load referred to the surface area) above the permissible limit. Then the oil film in these places becomes thin, and the surfaces of the shaft and bearing begin to touch along micro-roughnesses. A semi-liquid lubrication regime arises, characterized by an increase in friction and gradual heating of the bearing. This can then lead to so-called boundary friction with full contact of the surfaces, which will result in overheating, seizure (scuffing), sticking, melting and destruction of the bearing.
It is clear that the boundary friction mode is unacceptable in operation. However, it appears when the oil supply is disrupted, and this most often occurs due to its lack in the crankcase, that is, either due to the driver's oversight, or when the oil pan is damaged as a result of hitting an obstacle.
The semi-liquid lubrication mode is only permissible for a short time, when it does not have time to affect the wear of the bearing. Example: starting a cold engine. True, there is another danger here: at very low temperatures, the oil may be too viscous and its normal supply takes a long time to restore (20-30 seconds or more). Here, semi-liquid lubricant can already significantly affect the wear of parts.
The improvement of automobile engines is associated with a constant increase in rotation speed and power. At the same time, an increase in the compactness of designs is observed, including a reduction in the width and diameter of bearings. This means that the specific stresses in the node increase. And since the load on the bearing during engine operation cyclically changes in magnitude and direction, so-called fatigue failure of parts becomes a reality. To ensure the performance of bearings under such conditions, special designs, materials and technologies are required.
How it works
Typically, crankshaft bearings in modern engines are made in the form of thin-walled liners or bushings with a thickness of 1.0-2.5 mm (rarely more). The crankshaft main bearing shells are made thicker due to the need to accommodate a circular groove for supplying oil to the connecting rod bearings. The general trend is a reduction in the thickness of the bearing shells, which now averages 1.8-2.0 mm for main bearings and 1.4-1.5 mm for connecting rod bearings. The thinner the liners, the better they fit to the surface of the housing (bed), the better the heat dissipation from the bearing, the more accurate the geometry, the smaller the permissible gap and noise during operation, the longer the service life of the unit.
In order for the insert to take its exact shape when installed in the bed, it must be tensioned according to the bed diameter when free (so-called straightening)and a non-cylindrical shape of variable radius. In addition, for good adhesion to the surface and to prevent rotation, tension is also required along the length of the liner - this is called protrusion. All these parameters depend on the thickness, width and diameter of the liners, with the straightening being on average 0.5-1.0 mm, and the protrusion being 0.04-0.08 mm. However, this is still not enough for the bearing to operate reliably. Near the connector, the thickness of the liners is reduced by 0.010-0.015 mm to avoid scoring in these areas. They can appear due to deformation of the hole in the housing under the action of the working load, when the working clearance in the bearing is small.
The materials for the liners can vary. Their choice is linked to the material of the crankshaft and its heat treatment, the degree of engine boost and the specified service life. To a certain extent, the traditions of the automobile company also play a role here.
The inserts are always made multi-layered. The base of the insert is a steel strip, which ensures strength and reliability of the fit in the case. A layer (or layers) of a special antifriction material 0.3-0.5 mm thick is applied to the base using various methods. The main requirements for the antifriction material are low friction on the shaft, high strength and thermal conductivity (that is, the ability to conduct heat well from the surface to the bearing housing). The first requirement is best met by soft metals, such as alloys with a high tin and lead content (in particular, the widely known babbitts).
In the past, babbitts were widely used in low-power, low-speed engines. As loads increased, the strength of such liners with a thick layer of babbitt turned out to be insufficient. The problem was solved by replacing this entire layer with a kind of sandwich - lead-tin bronze covered with a thin layer (0.03-0.05 mm) a layer of the same babbitt. The insert has become multi-layered. In modern engines, "steel-bronze-babbitt" liners are usually made in 4 layers (under the babbitt there is still a very thin sublayer of nickel) and even 5-layer, when a thin layer of tin is applied to the working surface to improve the running-in. This is exactly what bearings look like on many foreign engines.
Along with this, steel-aluminum liners have also become widely used. The antifriction material here is an alloy of aluminum with tin, lead, silicon, zinc or cadmium, both with and without coatings. The most commonly used alloy in world practice is aluminum with 20% tin without coating. It withstands high loads and rotation speeds of modern engines, including diesels, and at the same time has satisfactory "softness". However, steel-aluminum liners are harder than babbitt ones (or with a babbitt coating), therefore more prone to scuffing under conditions of insufficient lubrication.
Auxiliary and camshafts of engines usually rotate at a lower frequency than crankshafts and experience much lower loads, so their operating conditions are easier. The liners and bushings of these shafts are usually made from materials similar to those described above. In addition, babbitt or uncoated bronze is sometimes used here. Often these bearings do not have bushings or liners at all and are formed directly by boring holes in the cylinder head. In such designs, the head is made of an aluminum-silicon alloy, which has good antifriction properties.
What modern engine bearings have in common, especially when it comes to crankshaft bearings, is that the material and design of the bearings match the material and operating conditions of the shaft (rotation speed, loads, lubrication conditions, etc.). Therefore, arbitrary replacement of parts, when, for example, during repairs, liners from another engine are installed, cannot be recommended. Otherwise, the service life of the repaired unit may be very short. To decide on such a step, you need to have the relevant information.
The inserts are very precise (precision) details. To ensure small (but quite specific - on average 0.03-0.06 mm) working clearances in bearings, during manufacturing the thickness of the liner is maintained with an accuracy of about 5-8 microns, and the length - 10-20 microns. Violation of these requirements can lead to a change in the working clearance in the bearing or the density of the fit of the liner in the housing, which is unacceptable due to a decrease in the reliability and service life of the entire engine as a whole.
Who produces them?
The complexity of the entire range of problems associated with the creation of high-quality automotive plain bearings has led to their production gradually being transferred to specialized firms. Abroad, many of these companies simultaneously produce other engine parts, and supplies go both to automobile plant conveyors and as spare parts. Some firms of this kind are part of well-known transnational manufacturing and trade and industrial corporations. Among the world manufacturers of bearings for engines, the following companies should be noted first of all: Kolbenschmidt (KS), Glyco, TRW, Sealed Power, Glacier, Clevite, Bimet. In recent years, such "luminaries" as Mahle and Goetze have also begun to make bearings. Among the "young" ones, it is worth mentioning the specialized company King (Israel), which began producing bearings in the early 80s.
Most of the listed manufacturers produce a huge range of bearings and supply their products as spare parts everywhere, including our market (through dealers or wholesale trading companies). Basically, of course, these are bearings for foreign engines - European, Japanese and American.
You can find both standard and various repair sizes of liners on sale (as a rule, no more than 0.75 mm) for most common models of Audi-Volkswagen, BMW, Mercedes, Ford, Opel, Fiat, Toyota, Nissan, Mitsubishi, Mazda, etc. For less common models, as well as when it is necessary to purchase liners of a larger repair size, you usually have to place an order and wait an average of 5-10 days (these terms vary among different trading companies).
The quality of such products usually does not raise any doubts either in terms of geometry or materials. However, if there is a choice and doubts about which manufacturer to give preference to, you should keep the following in mind. Companies such as Kolbenschmidt, Glyco, Glacier are some of the main suppliers of mass production. When buying their products, you can even get the same liners that were on the engine "from birth". The only difference will be the absence of the car manufacturer's emblem on the new parts. By the way, search for "relatives" (or so-called original) the use of repair size liners can be problematic. Not all automobile companies supply repair inserts in spare parts, and the price of inserts in "original" packaging is usually significantly higher than directly from their manufacturer.
Inserts from other, less reputable companies are usually cheaper, although it is difficult to detect differences in quality. Moreover, if there is a choice, then here you can try to take into account the operating conditions of the car. Thus, comparatively cheap liners, oddly enough, are somewhat better at resisting low-quality oils and oil filters that "walk" around our stores and markets than more expensive steel-bronze-babbitt ones. This, in particular, was demonstrated by the practice of using steel-aluminum liners from the King company in repairs instead of the standard bronze-babbitt ones - such a replacement does not harm the reliability of the engines, but allows for significant savings.
Some of the listed companies also produce liners for our machines. On our market you can already find these products for VAZ engines manufactured by Clevite, Bimet and Glacier. Of course, they are noticeably more expensive than domestic ones. However, it is not worth saving on liners when repairing domestic engines. Domestic products usually cannot stand comparison with imported ones. Thickness deviations for some of our commercial items reach 25-30 microns instead of the 8 microns specified by the tolerance. As a result, after being clamped by the cover, the inner surface of the bearing takes on an irregular shape, in which, for example, a gap of 0.07-0.09 mm in one section of the bearing can even turn into tension in another.
(Based on materials from the website: HondaBook.ru)