Types of crankshaft liners. Typical examples of crankshaft bearing shell wear. Incorrect processing of the crankshaft journals

Often on numerous forums devoted to automotive topics, you can read topics about knocking in the engine or about cranked liners. This is an emergency situation in the ICE. When they say that the liner has turned, this means that the plain bearings on and on the connecting rods have been pulled out of their seats and they have become unusable. This is a serious breakdown that happens quite often. Motorists see the reason in low-quality engine oils from an unknown manufacturer.

But there are much more reasons, and they are not directly related to the lubricant and its quality. As proof of this, there are many examples when the main liners fail if branded original oil is poured into the engine. Or vice versa - bearings work for more than one hundred thousand kilometers on medium-quality oils. Let's see why it cranks, what factors influence it and what is the main reason for this phenomenon.

Connecting rod bushing - what is it?

There is one very highly loaded part in the internal combustion engine. This is the crankshaft. The element is not installed on traditional bearings. Due to the design features used, the design of these same parts may be different. But the constant improvement of engines has led to the fact that now a sheet of steel is used, covered with a special anti-friction layer.

This is what these elements are installed in special places - beds. Inserts are fixed. The need to fix these parts is due to the fact that they have holes for the movement of oil. They must necessarily correspond to those in the beds. Also, with the help of fixation, friction is provided on special surfaces intended for this purpose. The connecting rod bearing is a kind of protective element, due to which the service life of the crankshaft is significantly increased.

The difference between main and connecting rod bearings

You need to know that there are two types of inserts. These are connecting rod and indigenous. The first are located between the connecting rod and the crankshaft journal. The root element is similar to the first in its purpose. However, it is located where the crankshaft passes in the engine housing. Inserts vary in size. Dimensions depend on the type of internal combustion engine for which a particular part is made. There are also special repair inserts. They are different from the original new ones installed in the engine. Repair liners differ only in marks that are multiples of 0.25 mm. So, their dimensions are approximately the same - 0.25 mm, 0.5 mm, 0.75 mm, 1 mm.

Reasons for turning the earbuds

So, the crankshaft is a part that works in harsh conditions, and it has to withstand enormous loads in extreme temperatures. In order for the mechanism to be securely held on the axis and to be able to ensure the correct operation of the entire crank mechanism, liners are needed. The journals on the shaft act as an inner race. Inserts - as external.

The engine block has channels for supplying pressurized lubricant. Due to the oil film that envelops the liners, the crankshaft can rotate. Why do car owners face situations when the crankshaft liners turned in the engine? There are several possible reasons. Let's take a look at them below.

Mechanical wear

The first reason why, when repairing an engine, the main and connecting rod bearings are replaced is exhaustion. Parts wear out due to mechanical stress. Many people try to save the earbuds, but it is useless. Physics is involved here, and physical processes cannot work differently. Wear is inevitable. The anti-friction layer on the liner is erased over time. This leads to free wheeling of the crankshaft. Loops appear. As a result, the oil pressure is reduced, and quite significantly. On most engines that are highly reliable, if the liner is turned, this indicates wear.

Turning the connecting rod bearings of the crankshaft

This is also one of the most popular faults. Many car owners have faced this problem. But not everyone knows about the reasons. Let's see what happens to the element. The connecting rod bearing plate is quite thin.

It is installed on a special seat. The outer walls on the semi-rings have special protrusions, which, even in an unrolled and undeveloped engine, rest against the front part of the cylinder block. At some point, the seat simply cannot hold the connecting rod bearing. As a result, a typical situation - cranked the liner. The plate not only rotates, but also sticks to the crankshaft journal. In this case, the engine stalls and will not start again.

Causes of broken connecting rod bearings

Experts see several reasons why plain bearings rotate. Often this is due to excessively thick oil, into which metal particles fall. Chip lubrication is abrasive to the bearings. Often there is a complete lack of oil. This is especially true for vehicles with worn oil scraper rings. Part of the lubricant just goes "into the pipe". As a result, the liner was cranked and the engine was sent for repair. The bearing caps may not be sufficiently tightened together. And finally, one more reason. It's too thin oil. Especially such products are harmful to motors operating under high loads.

Preload violation

If you cranked the liners, the reasons may be in this. In production cars assembled at the factory by qualified specialists, this will not happen. But if the motor has already been repaired, then, most likely, the selection of liners was performed incorrectly and the tightness was violated.

When the motor is running, the liners experience increased friction torque. This moment tends to crank the liner. And because of the reduced force that holds the part in place, the risk of turning increases exponentially. When subjected to an uneven load, a loose fit of the friction bearing causes the bushing to vibrate. The lubricating film is also broken. As a result, the part rotates, and the holding threshold is not able to prevent this.

How to identify a breakdown

When cranking, the crankshaft and cylinder block immediately fail. If the connecting rod bearings turn, the connecting rod itself, the crankshaft, and the cylinder block will fail. As a result, only a major overhaul of the motor can help the car owner. This breakdown can be identified. There are some signs of twisted liners. One of them is a characteristic metallic knock throughout the motor.

It does not stop even at idle, and with an increase in load, it knocks even more intensely. Another symptom is low oil pressure. If the engine is cold, then there may be no sound. If the situation is hopeless, the engine will stall, and it can only be revived by repair.

Repair and aftermath

A typical situation - cranked the liners. What to do? You can solve the problem in different ways, depending on the nature of the damage. In some cases, you can get by with replacing the liners with grinding the crankshaft. In difficult situations, repairs will be much more expensive.

If the connecting rod bearing has turned, then in modern engines this is not a serious problem. But this does not apply to the root. It often happens that the damaged liner simply changes, and the motor continues to work. Experts do not recommend this approach. The resource of the connecting rod-neck pair of the crankshaft restored in this way can be greatly reduced. A much more acceptable option is to replace the connecting rod with which the problem happened. Also, if the liners are cranked (including the VAZ-2172), the lock on the connecting rod will also break. It would be more optimal to bore the crankshaft to the next repair size and perform a complete replacement of the liners and connecting rods. after turning it is necessary without fail.

Seizures form on the neck of the mechanism. This is the only way to achieve the desired surface condition and the engine will work correctly.

What is the result

If something knocked in the motor, then this is a signal for the immediate termination of the operation of the car. You shouldn't start the engine. Most likely, the liners are turned inside the engine. Repairing this breakdown can be quite expensive. It should be taken into account that the temperature conditions of the motor operation also affect the resource of the elements. Do not overheat the engine. As for oil, it is safest to use products that fully comply with the requirements and tolerances of the manufacturer.

Conclusion

So, we found out for what reasons the crankshaft liners turn. To avoid damage, do not keep the engine at high speeds for a long time, change oil and filters on time, and observe the temperature regimes of the engine.

There are thousands of parts in an internal combustion engine. All of them are important to one degree or another and necessary for the balanced operation of a complex system. However, one cannot speak of their equivalence. The crankshaft, which directly transfers the energy of fuel combustion to the driving wheels, and all its associated parts are among the most important.

In particular, we are talking about crankshaft liners, small half rings made of metal that is softer than crankshaft steel and has a special anti-friction coating. During long-term operation of the engine, it is the liners that should fail first, and not the crankshaft journals.

The purpose of the crankshaft liners

The crankshaft liners are, in essence, plain bearings for connecting rods that rotate the crankshaft under the influence of microexplosion energy in the combustion chambers of the internal combustion engine cylinders.

In this system, rotational speeds and loads are high, so it is necessary to sharply reduce the friction of parts, otherwise the engine will fail almost instantly. To reduce the friction force, all significant internal interfaces of engine parts are in the so-called "oil mist", in a thin micron film, which is created by a special engine lubrication system.

A film enveloping metal parts is possible only with a sufficiently serious oil pressure. Between the liner and the crankshaft journal, there is just such an oil “layer”, due to which the friction force is sharply reduced. Therefore, the crankshaft liners are a protection that allows you to increase the service life of a part so important to the engine.

Types of crankshaft liners

First of all, the ICE crankshaft liners should be divided into two groups - main and connecting rod liners. The connecting rod bearings, as mentioned above, are located between the connecting rods and the crankshaft journals, and the main ones perform a similar role, but are placed between the crankshaft itself and those places where the crankshaft passes through the engine housing.

For each engine, the industry produces crankshaft liners (both connecting rod and main), differing from each other in their inner diameter. The diameters of the repair liners differ from each other and, accordingly, from the liners installed on the new engine, with a step of 0.25 mm. Thus, a size range of repair liners is compiled, each of which is larger in diameter (internal) than the factory ones by 0.25; 0.5; 0.75; 1 mm.

Checking and replacing the earbuds

Even with the correct operation of the lubrication system and constant care for it, over time, the effect of friction on the liners and the crankshaft itself is inevitable. This is manifested in the fact that roughness and grooves gradually form on the crankshaft journals. Pressurized oil passes freely through such “tunnels”, and the oil film does not form as it should. As a result, the friction forces increase and the crankshaft is subjected to more and more wear.

Therefore, after a certain number of kilometers (different for each brand of car), it is necessary to repair the engine, replacing the crankshaft liners with obligatory grinding of the crankshaft journals (eliminating roughness).

For different brands of cars, a number of repair sizes may be different. So, if for VAZ models there are 4 of them, then for GAZ - 6, with the same step. Some manufacturers put their size on the crankshaft liners. If, for example, "0.25" is written on the liner, this means that such an liner has the 1st repair size.

The size of the liners that will need to be installed at the end of the repair also depends on the degree of roughness, which will be eliminated by boring and grinding. It may well be that with heavy wear, the 1st repair size will need to be skipped, immediately moving on to the second.

One way to check the degree of wear of the liners (other than directly measuring their thickness) is to use a set of special control probes made of paper or copper foil. The probes are thick in 0.025 mm increments. Installing the probe between the liner and the neck of the shaft, tighten, as expected, all connections, and then try to turn the crankshaft. This operation is performed until the crankshaft rotates with a noticeable effort. The value of the thickness of the probe used will correspond to the size of the gap.

At the same time, copper probes are lubricated with oil, and the shaft is rotated no more than 90 degrees to avoid damage to the surface of the liner.

It is best to entrust the work of checking, selecting and replacing crankshaft liners to specialists who know a lot about this kind of business and have considerable experience. In each case, individual features and subtleties are possible that an ignorant person may not notice. Namely, they will then negatively affect the entire result of the work. Be wise - entrust complex work to professionals!

The vehicle engine is a complex unit, consisting of thousands of different parts. In order for the internal combustion engine system to work in a balanced way, all elements of the unit must function properly. In this article we will talk about liners for crankshaft repair: what is their purpose, what marking and how to replace components.

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Description of crankshaft bearings

All main and connecting rod journals of the crankshaft have their own dimensions, we are talking about the parameters that the journals take after the grinding process. The dimensions of these elements must fully comply with the dimensions that the crankshaft repair liners have. Accordingly, when buying such spare parts, it is necessary to take into account the parameters of your vehicle, because each individual motor has its own dimensions.

For example, if you own a classic VAZ car, you should keep in mind that domestic cars have four different sizes of liners. This means that the crankshaft can in principle be bored no more than four times. You also need to take into account that the crankshaft liners also have an outer size that never changes, but the inner one can be adjusted due to an increase in the thickness of the elements.

Purpose of inserts

In fact, the main bearings of the crankshaft, regardless of the marking, act as bearings designed to improve the sliding of the connecting rods. Connecting rods, as you know, are designed to rotate the crankshaft under the influence of a microexplosion of the combustible mixture in the combustion chambers of the engine. Since the elements wear out periodically, the motorist must remove and replace them in a timely manner, which should also be accompanied by a shaft bore.

It is no secret that when the engine is running, internal components are subjected to high loads and rotational speeds. This means that the motor simply needs to reduce friction, otherwise the unit may fail almost immediately. In order for the friction force to be significantly lower, all the necessary components inside the motor function in a micron film, which is oil.

This layer, which envelops the metal components of the unit, is formed only with sufficient pressure of the working fluid. In particular, the film must always be between the crankshaft main journal and the liner, as a result of which the friction index is not as high as it could be. Accordingly, the liners, which are made of metal, are a reliable protection that allows you to increase the service life of the shaft as a whole.

Design

It would seem that the crankshaft liner is a common part, but its manufacture is carried out using several different metals.

Accordingly, the liner consists of several layers, which we will consider below:

the first layer is made of copper, its percentage can be from 69 to 75%;
the manufacture of the second layer is carried out from lead, its percentage is from 21 to 25%;
the third layer is tin, about 2-4%.

In general, the total thickness of the liner is 250-400 microns. It should be noted that sometimes not copper, tin and lead are used for the manufacture of the liner, but a specialized aluminum alloy. Marking in this case will depend solely on the manufacturer.

Kinds

As for the types, the marking here will depend on the type of component.

In general, liners for the crankshaft are divided into several groups:

Indigenous. Regardless of the marking, the main bearings perform similar functions. They are mounted between the crankshaft and the place where this shaft passes through the motor housing.
Connecting rod. The connecting rod components are located directly between the connecting rods and the shaft journals.

In principle, liners, both connecting rod and main, are produced for each type of motor, but they all differ in inner diameter. Depending on the engine model, the diameters of the elements will be different, even for one engine. As a rule, the difference in diameter, that is, the pitch, is 0.25 mm. This means that the size range of parts is as follows: 0.25 mm, 0.5 mm, 0.75 mm, etc.

Checking and replacing the earbuds

When do you need to change?

Since the crankshaft operates under conditions of high temperature and physical stress, only bearings can keep it on its axis. The necks, both main and connecting rod, play the role of internal clips, but the liners are external. Like other engine components, liners wear out over time, which leads to the need to replace them.

Physical wear is an important condition in which it becomes necessary to remove and replace elements. As much as the motorist would not want to avoid wear and tear, this is impossible. Operating a vehicle with worn parts can result in engine failure.

However, the need to remove and install new parts may arise in other cases. For example, often domestic motorists are faced with such a problem as turning the liners. A thin plate of the element is mounted in a special groove, and from the outside, the protrusions abut against the end parts of the bearings. In some cases, when the loads are very high, the protrusions are not able to hold the liner, causing the latter to rotate.

In this case, further operation of the internal combustion engine will be impossible, this malfunction occurs for the following reasons:

as a result of using a very viscous oil;
in the absence of lubricating fluid or ingress of abrasive into it;
with very low interference when mounting bearing caps;
if the oil is not viscous enough;
if the engine is regularly operated under conditions of high loads and overloads.

signs of wear

If you have already understood that the repair of the motor of your car is inevitable, then you will probably be interested in identifying the wear of the elements. To determine the measurements, you will need a micrometer, but you can also visually identify the breakdown. During the inspection, you will also need to evaluate the possibility of subsequent boring of the shaft.

But if the liners began to rotate, then their removal and installation of new ones should be done as quickly as possible. One of the signs of wear is a loud knocking of the shaft, a decrease in engine power, as well as its regular attempts to stall.

In the event that the necks are jammed, then driving a car will be impossible. One way or another, but you will have to carry out a detailed inspection of the elements. If wave-like damage is detected on the necks, which, in principle, can be felt with your hands, then the crankshaft needs to be bored. Accordingly, the replacement of the crankshaft liners in this case will also be necessary. If you are going to buy new parts, then it is better to do this after the motor has been bored out, because if the wear is large enough, then you can miscalculate with the size.

Replacement sequence

To date, the procedure for removing and installing crankshaft liners is not particularly popular among our motorists. Drivers in most cases trust this procedure to specialists, but some still decide to replace the elements at home. We recommend doing repairs with your own hands only if you have at least some knowledge.

In general, the process of replacing the earbuds is described below:

Before proceeding with the replacement of components, it is necessary to check the presence of a gap between the shaft and the liner. To do this, you will need to use the calibrated plastic wire that is on the neck. Then the cover from the elements is installed and tightened with the necessary force, in this case this figure is 51 Nm. All measurements should be made with a torque wrench.
When the cover is removed, the gap will correspond to the degree of flattening of the wire. To evaluate the desired parameter, you should use the nominal clearance, this indicator should be indicated in the service manual for your car. In the event that, when checking the gap, you find that it is greater than that specified by your automaker, then the liners will have to be changed. The purchase of liners is carried out strictly in accordance with your car model, if the gap is too large, then buy parts only after the shaft has been bored.
When all the gaps have been measured, it will be necessary to dismantle the connecting rods from all necks. Then the crankshaft is removed and its boring is carried out. The grinding process itself should take place on the centripetal. Naturally, such a device is unlikely to be found in the garage of an ordinary motorist, so it would still be better to entrust the grinding procedure to professionals.
When the crankshaft is bored out, proceed to the selection of repair liners. In this case, you will again have to use a micrometer, then try on the shaft liners. When removing old liners, pay attention to their condition - perhaps their failure is due to external mechanical influences. So that the malfunction does not recur after a while, it is desirable to eliminate the cause, of course, if it exists in principle. After all, as you remember, the failure of the liners can be the result of physical wear and tear.
Only after you have finally chosen the parts for repair, you can begin the process of installing the crankshaft. All installation steps are carried out in reverse order, everything must be done correctly and strictly in accordance with the requirements of the automaker. Only when all components are in place can the main bearing caps be screwed on.
After that, proceed to the installation procedure directly of the shaft liners themselves, as well as the connecting rods. In general, this process should not take much time and effort. Repair liners must be lubricated with engine fluid, after which their covers are screwed on. Actually, the installation itself is quite simple, except for the preparatory processes.

When operating your “iron horse”, always remember that the crankshaft is one of the most expensive in terms of repair and replacement of components. Moreover, it experiences very serious loads during operation. Accordingly, you, as a driver, need to take all measures in order to increase its service life. And an important procedure for this is boring, which must be carried out on time. If the boring process is performed correctly, then all the necks will be smooth, respectively, they will be able to withstand heavy loads during operation.

Also keep in mind that the vehicle's motor is a rather complex unit in its design. And although some experts can disassemble and assemble it with their own hands even with their eyes closed, dismantling and assembling the crankshaft still requires specific skills. Therefore, in the absence of good experience, we do not recommend that you take up this business. After all, by pulling or not pulling the liners during installation, you can again encounter the problem of turning them.

The crankshaft bearings are plain bearings for the connecting rods that rotate the shaft. The rotation here is the result of a microscopic explosion occurring in the combustion chambers of the engine cylinders.

The high speed and heavy loads that occur in this system make it necessary to minimize the friction of the parts between themselves, otherwise the engine will fail almost instantly. And this is absolutely unacceptable. What helps to protect the motor?

To prevent this from happening, significant engine parts have a thin oil film, which is provided by a special lubrication system of an automobile motor. The appearance of such protection is possible only with a fairly strong oil pressure. That is, the crankshaft liners provide some protection that extends the life of such an important part.

There are connecting rod and crankshaft main bearings. The first are located between its connecting rods and necks. Indigenous have a similar role, but their location corresponds to the space between the crankshaft and its passage through the body of the internal combustion engine.

Causes of failure

Due to high loads, these parts of the crankshaft have an increased risk of breakage. The main causes of problems with these elements are their physical wear and tear. The former is considered a natural failure, as they tend to wear out over time, leading to more shaft travel and reduced oil flow due to low pressure.

The second situation occurs because the plate of the insert element is too thin and when turning it sticks to the crankshaft journal. This actually leads to engine failure. The reasons for the second case may be as follows:

limiting indicators of the viscosity of the lubricant, the ingress of harmful impurities into it or the complete absence of it;
poor tension for supplied bearing caps;
the lubricant is too thin;
the engine is often operated under conditions of regular overloads.

All this leads to the breakdown of these components and actually makes it impossible to operate the engine. Therefore, it is important, upon detection of the indicated malfunction, to replace the broken parts with new ones and to carry out their full installation.

Installation order

Most often, these elements are put in auto repair shops, where experienced specialists work. However, if a person has certain repair skills and is good at handling tools, then you can try to install the crankshaft elements yourself. To do this, you must follow the following procedure:

The clearance between the shaft and the bearing is checked. It uses plastic wire. It is tightened with a force of 51 newtons per meter and then the existing gap is determined by the degree of flattening of the wire. If it is greater than the nominal, then the liner needs to be replaced.
All connecting rods are removed from the rails, the crankshaft is dismantled and bored. Then a repair element is selected. These procedures should be carried out on a centripetal, it is also important to have a micrometer.
After selecting the element, the crankshaft is reassembled. The components are inserted into their seats and the main bearing caps are screwed on.
Put the crankshaft and connecting rods back. The liners are lubricated with oil and their covers are screwed on. As a result, the process is completely completed, the liners will work for a long time.

The direct installation of such elements takes a relatively small amount of time compared to preparatory measures and additional work. And this means that if there is a great desire and appropriate skills, everyone can insert the liners on their own.

Conclusion

The crankshaft is considered an important and very expensive part of the car, which operates under incredibly heavy loads. Therefore, it is important to do everything in order to extend the period of its operation. A timely measure will be the boring of the shaft and the correct replacement of the liners. All this will help to make the elements of the mechanism smoother and stronger, so that they are almost immediately ready for work.

Inserts can be purchased separately or as a set. The important point here is that for each car there are standard liners that help in the future to select elements similar in their characteristics. Successful operation of the crankshaft and the car as a whole!

An analysis of the condition of the replaced bearings made it possible to classify the damage as follows: bearing scuffing, increased or uneven wear of the liners, fatigue wear of the antifriction layer, corrosive wear, fretting corrosion of the seating surface, cavitation wear, loss of preload.

The nature of the distribution of these types of damage depends on various factors, including the type of engine, the materials used for friction pairs, the type of lubricants and fuels, and operating conditions. So, for bearing shells made of bronze with BK2 babbit filling, most of all, bearing shells are replaced for fatigue wear of the antifriction layer. At the same time, for bearings with liners made of steel filled with lead bronze BrSZO, which has a higher fatigue strength than babbitt, liners are replaced most of all in terms of scuffing and corrosion wear of the antifriction layer (Table 1.1).

Table 1.1 - Classification of damage to bearing shells

A significant difference in the number of connecting rod bearings replaced by scuffing compared to the main bearings already depends on the difference in design, loading conditions, and, ultimately, on the friction mode of these bearings.

Among all types of bearing damage, scoring has the most serious consequences, causing in some cases breakage of the crankshaft, overheating and scoring of the piston, destruction of the cylinder liner, connecting rod, and sometimes the cylinder block. Seizure is associated with a violation of the liquid friction mode and increased heat release of the friction pair.

In the initial stage, this is the so-called “burning”, and in the developed stage, it is accompanied by the melting of the antifriction material and the destruction of the liners. A characteristic sign of overheating of liners during "burning", especially those with anti-friction material and the base of which have a significant difference in the coefficients of linear expansion (for example, steel-lead bronze), is a decrease in the diameter of the liner in the free state.

Seizure can occur both on one or two liners of a given diesel engine, and on all or many bearings at once. In the latter case, it is associated with violations in the lubrication system: failure of the oil pump, damage to the oil supply pipes, and also when the lubricant is flooded. The reasons for the scuffing of individual bearings can be assembly defects, the ingress of dirt and large particles, the presence of bearing defects. However, in the case of systematic seizures, their cause is the insufficient bearing capacity of the bearing. A typical view of the liner after tearing is shown in Figure 1.23 a.

It is known that scuffing occurs more often in bearings for which solid antifriction materials are used: lead bronze, aluminum-tin. At the same time, it was noted that the most severe consequences of scuffing are in cases where liners filled with lead bronze are used. Already in the initial stage of scuffing, the surface of the neck is covered with a network of thermal cracks, which can cause crankshaft breakage. There are cases when the failure of the shaft occurred just on those necks on which the liners were replaced due to scuffing.

When bearings with shells that have an aluminum-tin layer are seized, as long as the layer is retained, the tin is transferred to the shaft journal and thereby protects the journal from more serious damage.

Seizure can also occur during operation of bearings with liners filled with soft antifriction materials such as babbitt.

As can be seen from Table 1.1, one of the reasons for the rejection of crankshaft bearing shells is fatigue wear. Fatigue wear of the bearing shells of diesel locomotives manifests itself in the form of spalling of the antifriction layer.

Liners with an anti-friction layer of babbitt are most susceptible to fatigue wear. A typical view of fatigue damage to BK2 babbitt on liners is shown in Figure 1.23 b. There are cases of occurrence of fatigue wear of bearings with stronger materials (lead bronze, aluminum-tin alloys).

In the event that the liner has a soft running-in coating of a significant thickness of 0.04-0.06 mm, fatigue wear of this coating may occur (Figure 1.23 c). The causes of fatigue damage should be considered as a cyclic change in stresses in the antifriction layer during engine operation. The development of fatigue damage is accelerated due to deformation of the assembly parts, the presence of deviations in its geometry, and other factors.

When analyzing the stress state of the antifriction layer, three stress components can be distinguished: compressive static stresses that occur during the installation and tightening of the liners in the supports; static thermal stresses from the temperature difference of the liner along the thickness and the difference in the coefficients of linear expansion of the housing and liner materials, dynamic stresses determined by the variable forces acting on the bearing. The static stress component depends on the bearing fit parameters. During operation of the engine, under the action of variable forces, the housing and bearing are bent, leading to a cyclic change in the compression stresses on the working surface.

The initiation of fatigue cracks can be influenced by microstructural defects or microcracks that occur in the region of maximum stresses when the fluid friction regime is violated, for example, when starting or stopping a diesel engine. Subsequently, cracks develop into the depth of the antifriction layer and, having reached a more durable material of the liner base, propagate along it. The spalling of a section of the antifriction layer occurs when it encounters another crack that develops from the surface.

Lubrication influences the occurrence and development of fatigue damage. The aggressive action of the oil reduces the fatigue strength of the bearings.

The chemical composition of the babbitt has a great influence on the durability of bearing shells. For example, a deviation from the optimal sodium content in BK2 babbitt (over 0.4%) increases the failure of the liners. The durability of bearings with a layer of babbitt largely depends on the quality of the filling. Common filling defects are friability, porosity and low adhesion strength of the antifriction layer to the base of the liner. In this case, shrinkage ripples can be quite small and affect only after long-term storage of the liners.

As can be seen from the data in Table 1.1, a significant part of the liners is replaced due to corrosive wear. Bearings whose anti-friction material has a lead base, such as lead bronze, are subject to this type of wear. Corrosion is caused by products of oil oxidation due to the ingress of water, fuel and some oil additives into it.

Erosive wear of liners can occur due to the action of electric current. The greatest erosive wear is noted on liners located close to the generator. As the supports moved away from the generator, the wear of the liners decreased.

The working surface of the liners exposed to electroerosion is covered with a small rash (Figure 1.23 e), leading to a high wear rate of individual liners.

Wear due to fretting corrosion occurs due to micro-movements of surfaces. Significant signs of wear from fretting corrosion occur when insufficient bolt tightening is loosened, plastic deformations of the ends of the liners and other violations of their fit. In this case, microseizures, overheating, deterioration of fit and changes in the geometry of the working surface are possible. A view of the liners with traces of fretting corrosion is shown in Figure 1.23 f.

The main consequence of this process is the weakening of the fit and rotation of the liner, which in turn entails seizure of the shaft journal, completely disrupts the supply of lubricant to the piston, followed by seizure of the piston and cylinder liner.

The reasons leading to damage to the liners are different, in general they can be divided into those determined by the operating conditions of the bearing and the reasons that do not depend on these conditions. The reasons depending on the operating conditions of the bearing assembly include an incorrectly selected bearing capacity margin, incorrectly accepted macro- and microgeometric relationships in the bearing assembly, the absence or incorrect choice of counterweights, non-optimal clearances, an unsuccessfully matched shaft-bearing friction pair, incorrect location lubrication supply, lubrication grades, etc.

Causes that do not depend on the design of the bearing assembly include failure of the piston, connecting rod, breakage of bolts, damage in the block, breakage of the crankshaft, ingress of water and other impurities into the lubricant, interruption of the lubrication supply (pump failure or other malfunctions of the lubrication system). ), insufficient filtration of the lubricant; incorrect diesel engine running-in mode or violation of the operating rules (especially violation of the temperature regime: start-up-stop); incorrect adjustment or failure of the diesel emergency protection; violation of the technology of assembly and disassembly of the bearing unit; unreasonably frequent disassembly of the bearing assembly, exposure to electrical potential, vibration; use of liners with an expired shelf life, etc.