Tightening torque of connecting rod bolts. How and with what force to tighten the connecting rod and main bearings

Many motorists who are used to repairing their car themselves know firsthand that engine repair is a very difficult and responsible task.

Since the repair of the power unit requires from the motorist not only certain skills, but also knowledge for the correct implementation of the technological process. Today in the article we will briefly consider the crank mechanism, its role in the car engine.

In addition, we will also talk about the importance of observing the tightening torque of the main and connecting rod bearings, the nuances and sequence of this operation, and other important aspects. Therefore, it will be useful for beginners to somewhat expand their knowledge on the topic by reading our article.

The concept of KShM

The crank mechanism, abbreviated as KShM, is the most important unit of the unit for the engine. The main task of this mechanism is to change the rectilinear movements of the piston into rotational, and vice versa. This moment of rotation occurs due to the combustion of fuel in the engine cylinders.

As you know, gases during the combustion of the fuel mixture tend to expand. Then, under high pressure, they push the engine pistons down, and they, in turn, transfer force to the connecting rods and the crankshaft. It is due to the specific shape of the crankshaft in the motor that one movement is converted into another, which ultimately allows the wheels of the machine to rotate.

In terms of its functions, the crankshaft is the most loaded mechanism of the engine. It is this node that determines which form this or that power unit will have and how the cylinders will be located in it. This is due to the fact that each type of engine is created for a specific purpose. Some vehicles require maximum engine power, light weight and dimensions, while others prioritize ease of maintenance, reliability and durability. Therefore, manufacturers produce various types of crank mechanisms for different types of engines. KShM are divided into single-row and double-row.

The role of the crankshaft liners

The crankshaft must withstand heavy loads during engine operation. But bearings for this device cannot be used. This role was taken over by the main and connecting rod bearings. Although in their task they perform the functions of plain bearings. The liners are made from a bimetallic strip consisting of low carbon steel, copper and lead, as well as ACM aluminum alloy or babbitt.

It is thanks to the liners that the free rotation of the crankshaft is ensured. To ensure durability and wear resistance, the liners are coated with a thin, micron-sized layer of oil during engine operation. But for their complete and high-quality lubrication, high oil pressure is simply necessary. This role was taken over by the engine lubrication system. All these conditions just help to reduce the friction force and increase the life of the engine.

Types and sizes of liners

In general, crankshaft liners are divided into two groups:

1. The first type is called root bearings. They are located between the crankshaft and the places of its passage through the motor housing. They bear the greatest load, since it is on them that the crankshaft is fixed and rotates.
2. The second group includes connecting rod bearings. They are located between the connecting rods and the crankshaft, its necks. They also carry huge loads.

Main and connecting rod bearings are made for each type of engine individually with their own dimensions. Moreover, for most automobile engines, in addition to the nominal, factory sizes, there are also repair liners. The outer size of the repair liners remains unchanged, while the inner diameter is adjusted by increasing the thickness of the liner. In total there are four such sizes with a step of 0.25 mm.

It is no secret that with high mileage of the car, not only the main and connecting rod bearings wear out, but also the crankshaft journals. These circumstances lead to the need to replace liners of nominal sizes with repair ones. To put one or another repair insert, the neck is bored to a certain diameter. Moreover, the diameter is selected for each of the dimensions of the liner individually.

If, for example, a repair size of 0.25 mm has already been used, then when getting rid of flaws on the crankshaft journals, a size of 0.5 mm should be used, and for serious scuffing, 0.75 mm. With the correct replacement of the liners, the engine should work for more than one thousand kilometers, unless, of course, other car systems are working.

There are also options when boring is not required and the liners are simply changed to new ones. But people who do this professionally do not advise simply changing the liners to new ones. This is explained by the fact that during the operation and operation of the liners, microdefects still occur on the shaft, which are not visible at first glance. In general, without grinding, there is a possibility of rapid wear and a small KShM resource.

Signs of wear on the crankshaft bearings

In the conversations of motorists, the phrases are often heard: “The engine knocked” or “The liners cranked”, these words most often refer to the wear of the liners. This, in turn, is a serious breakdown in the motor. The first signs of such malfunctions are the loss of oil pressure or the appearance of extraneous sounds during engine operation. It will be difficult for an inexperienced motorist to determine the signs of a malfunction of the liners, so it is better to immediately contact a specialist.

For a professional to listen and make a diagnosis will not be a serious problem. Usually, this procedure is performed at idle engine speed, by sharply pressing the gas pedal. It is believed that if the sound is a dull tone or iron grinding, then the problem is in the main bearings. If the connecting rod bearings fail, the knock is louder and stronger.

There is another way to check wear. It is necessary to alternately unscrew the spark plugs or nozzles for diesel engines. If the knock disappears when you unscrew a candle, then this is the cylinder in which there are problems.

The problem of low oil pressure may not necessarily appear from wear of the liners. It is possible that the oil pump, the pressure reducing valve is faulty, or the camshaft bed is worn out. Therefore, we first check all the nodes of the lubrication system and only after that we draw conclusions about what exactly to repair.

We measure the gap between the liner and the crankshaft

Inserts are produced in 2 separate parts with special places for mounting. The main task during assembly should be to ensure the required clearance between the shaft journal and the liner. Usually, a micrometer is used to determine the working gap between them, and the inner diameter of the liners is measured with an inside gauge. After that, some calculations are made, which make it possible to identify the gap.

However, it is much easier to do such an operation using a special plastic calibrated wire. Pieces of the required size are placed between the liner and the neck, after which the bearing is clamped with the required force and disassembled again. Next, a special ruler is taken, which comes with the wire in the kit, and the width of the corresponding imprint on the shaft is measured. The wider the crushed measuring strip, the smaller the clearance in the bearing. This method allows you to control the required distance between the neck and the liner with high accuracy.

How and with what force is the main and connecting rod bearings tightened?

It is possible to tighten the main and connecting rod bearings with the required force with a special torque wrench. The wrench can be either with a ratchet or with an arrow. Both wrenches are stamped with the dimensions required to tighten nuts and bolts to any torque. To set up, you will need to set the required value on the key, and after that you can immediately start tightening.

At the same time, remember that for a force of less than 5 kg, there is no need to put a pipe on the wrench in order to create additional leverage. This can be done with one hand to avoid stripping the bolt threads.

Tightening torque for main and connecting rod bearings

Before installing the liners, the first step is to remove the preservative grease from them and apply a small layer of oil. Next, we install the main bearings in the bed of the main journals, while not forgetting that the middle liner is different from the others.

The next step is to put the covers on the beds and tighten them. Moreover, the tightening torque must be applied in accordance with the standards, which are sometimes indicated in the rules for operating the vehicle. But most often there are cases when the technical manual for the car does not indicate the tightening torque for the main and connecting rod bearings. In such cases, it is recommended to look for this information in the special literature on the repair of a particular engine. For example, for Lada Priora cars, the tightening torque of the bed cover is from 64 N * m (6.97 kgf * m) to 81 N * m (8.61 kgf * m).

Next, we proceed to install the connecting rod bearings. In this case, you should pay attention to the correct installation of the covers, each of them is marked, so do not mix them up. The tightening torque they have is much less than that of the indigenous ones. For example, if you take the tighter model "Lada Priora", the tightening torque of the connecting rod bearings will start from about 43 N * m (4.42 kgf * m), up to 53 N * m (5.46 kgf * m).

Please note that the data given as an example assumes the use of new liners for repair, and not used parts. Otherwise, when using the old liners, the tightening torque should be selected based on the upper limit of the recommended torque from the documentation for this engine. This is done due to the possible presence of some wear on old parts. Sometimes ignoring this fact can lead to significant deviations from the recommended norm.

When all the bolts are tightened for the first time, it is advisable to scroll the shaft. To do this, on the side of the crankshaft there is a place for a wrench, we calmly scroll it clockwise. If the ring burst or there is any other malfunction, then this will be immediately visible. Further, making sure that there are no problems, we check again all the bolts with a wrench at the moment of tightening.

It should be remembered that the tightness of the sliding bearings to the crankshaft and, accordingly, the efficiency of the engine itself depends on how correctly this process is performed. Since if the bolt is not fully tightened, there will be excess oil, the entire lubrication cycle will be disrupted, and it can also lead to breakage of the liner. If we overtighten, then the liner will overheat, the lubricant will no longer be enough. In the end, the liner may even melt and crank, which will lead to an overhaul of the engine.

Rating 3.50

There is nothing to do in engine repair without a torque wrench! Tightening torques when repairing a Honda Civic are very important. Honda engineers calculated a different torque for every bolt and nut in the car. Tighten by hand to a characteristic crunch is not necessary. Firstly, you can break some kind of bolt, and it will be extremely difficult to get it out. Secondly, a skewed cylinder head will clearly let oil and coolant through. The Honda Civic, like any other car, uses different tightening torques, from 10 Nm to 182 Nm and even more, the crankshaft pulley bolt. I advise you to purchase a powerful torque wrench, powerful and good, with click to reach the moment, do not take arrow. And lastly, all connections that are part of one element (disk, cylinder head, covers) are tightened in several stages from the center outward and in a zigzag. So, in order, I describe everything in Nm (Nm). Don't forget to lightly grease the threads with oil or copper grease.

These moments fit for all D Series D14,D15,D16. Did not check D17 and D15 7th generation.

Tightening torques for cylinder head bolts

On earlier versions, there were only two stages, later already 4. Important It is advisable to stretch the bolts and generally work with threaded connections at a temperature of at least 20 degrees Celsius. Do not forget that you need to clean the threaded connections from any liquid and dirt. It is also advisable to wait 20 minutes after each stage to relieve the "stress" of the metal.
P.S. Different sources give different numbers, for example 64, 65, 66 NM. Even in the original reference books for different regions, I write here the average or the most familiar ones.

• D14A3, D14A4, D14Z1, D14Z2, D14A7 - 20 Nm, 49 Nm, 67 Nm. Control 67
• D15Z1 - 30 Nm, 76 Nm Control 76
• D15Z4, D15Z5, D15Z6, D15Z7, D15B (3Stage) - 20 Nm, 49 Nm, 67 Nm. Control 67
• D16Y7, D16y5, D16Y8, D16B6 - 20 Nm, 49 Nm, 67 Nm. Control 67
• D16Z6 - 30 Nm, 76 Nm Control 76

• Valve clearance locknut d16y5, d16y8 - 20
• Valve clearance locknut D16y7 - 18
• Banjo fuel hose bolt d16y5, d16y8 - 33
• Banjo bolt fuel hose D16y7 - 37

Other tightening torques

• Nuts on discs 4x100 - 104 Nm
• Spark plugs 25
• Hub nut - 181 Nm

Learn something new

This article is relevant for 1992-2000 Honda vehicles such as Civic EJ9, Civic EK3, CIVIC EK2, CIVIC EK4 (partially). The information will be relevant for owners of Honda Integra in DB6, DC1 bodies, with ZC, D15B, D16A engines.

The internal combustion engine structurally has a large number of mating parts that experience significant loads during operation. For this reason, the assembly of the motor is a responsible and complex operation, for the successful completion of which the technological process must be observed. The performance of the entire power unit directly depends on the reliability of fixation and the accuracy of the fit of individual elements. For this reason, an important point is the exact implementation of the design interfaces between mating surfaces or friction pairs. In the first case, we are talking about fastening the cylinder head to the cylinder block, since the bolts must be pulled with a strictly defined force and in a clearly marked sequence.

As for the loaded rubbing pairs, increased requirements are put forward for the fixation of connecting rod and main bearings (main and connecting rod bearings). After repairing the engine during the subsequent assembly of the power unit, it is very important to observe the correct tightening torque for the main and connecting rod bearings of the engine. In this article, we will look at why it is necessary to tighten the liners with a strictly defined force, and also answer the question, what is the tightening torque of the main and connecting rod bearings.

Read in this article

What are plain bearings

To better understand why the liners in the engine need to be tightened with a certain torque, let's take a look at the function and purpose of these elements. Let's start with the fact that these plain bearings interact with one of the most important parts of any internal combustion engine -. In short, the reciprocating motion in the cylinder is converted into rotational motion precisely because of the crankshaft. As a result, a torque appears, which is eventually transmitted to the wheels of the car.

The crankshaft rotates constantly, has a complex shape, experiences significant loads and is an expensive part. To maximize the life of the element, the design uses connecting rod and main bearings. Given the fact that the crankshaft rotates, as well as a number of other features, conditions are created for this part that minimize wear.

In other words, the engineers abandoned the decision to install conventional ball bearings or roller type bearings in this case, replacing them with main and connecting rod plain bearings. Main bearings are used for the main journals of the crankshaft. The connecting rod bearings are installed at the point where the connecting rod meets the crankshaft journal. Often, main and connecting rod plain bearings are made according to the same principle and differ only in the inner diameter.

For the manufacture of liners, softer materials are used compared to those from which the crankshaft itself is made. Also, the liners are additionally coated with an anti-friction layer. Lubricant (engine oil) is supplied under pressure to the place where the liner is mated with the crankshaft journal. The indicated pressure is provided by the oil pump. In this case, it is especially important that there is the necessary clearance between the crankshaft journal and the plain bearing. The quality of lubrication of the rubbing pair, as well as the indicator of engine oil pressure in the engine lubrication system, will depend on the size of the gap. If the gap is increased, then the lubricant pressure decreases. As a result, the crankshaft journals wear out quickly, and other loaded nodes in the internal combustion engine device also suffer. In parallel with this, a knock appears in the engine.

We add that a low oil pressure indicator (in the absence of other reasons) is a sign that the crankshaft needs to be ground, and the engine liners themselves need to be changed taking into account the repair size. For repair liners, an increase in thickness by 0.25 mm is provided. As a rule, there are 4 repair sizes. This means that the diameter of the repair insert in the last size will be 1 mm. less than standard.

The plain bearings themselves consist of two halves, in which special locks are made for proper installation. The main task is to ensure that a gap is formed between the shaft journal and the liner, which is recommended by the engine manufacturer.

As a rule, a micrometer is used to measure the neck, the inner diameter of the connecting rod bearings is measured with an inside gauge after assembly on the connecting rod. Also, for measurements, you can use control strips of paper, use copper foil or control plastic wire. The gap at the minimum mark for rubbing pairs should be 0.025 mm. An increase in clearance to 0.08 mm is a reason to bore the crankshaft to the next repair size

Note that in some cases, the liners are simply replaced with new ones without boring the crankshaft journals. In other words, it is possible to manage only by replacing the liners and get the desired gap without grinding. Please note that experienced professionals do not recommend this type of repair. The fact is that the resource of parts at the mating point is greatly reduced even taking into account the fact that the gap in the rubbing pair is normal. The reason is considered to be microdefects, which still remain on the surface of the shaft journal in case of refusal to grind.

How to tighten main bearings and connecting rod bearings

So, in view of the foregoing, it becomes clear that the tightening torque of the main and connecting rod bearings is extremely important. Now let's move on to the build process itself.

1. First of all, root bearings are installed in the bed of the root necks. Please note that the middle liner is different from the others. Before installing the bearings, the preservative grease is removed, after which a little engine oil is applied to the surface. After that, bed covers are placed, after which a tightening is carried out. The tightening torque must be the one recommended for the specific power unit model. For example, for engines on the VAZ 2108 model, this figure can be from 68 to 84 Nm.
2. Next, the connecting rod bearings are installed. During assembly, it is necessary to accurately install the covers in place. These covers are marked, that is, their arbitrary installation is not allowed. The tightening torque of the connecting rod bearings is slightly less compared to the main ones (the indicator is in the range from 43 to 53 Nm). For Lada Priora, the main bearings are tightened with a force of 68.31-84.38, and the connecting rod bearings have a tightening torque of 43.3-53.5.

It should be added separately that the indicated tightening torque assumes the use of new parts. If we are talking about an assembly that uses used parts, then the presence of wear or other possible defects may lead to a deviation from the recommended standard. In this case, when tightening the bolts, you can push off the upper bar of the recommended torque, which is indicated in the technical manual.

Summing up

Although the torque of the main and connecting rod bearing caps is an important parameter, quite often the torque value is not indicated in the general technical manual for a particular vehicle. For this reason, you should separately look for the necessary data in the special literature on the repair and maintenance of a particular type of internal combustion engine. This must be done before installation, which will allow the repair work to be carried out correctly, as well as to avoid possible consequences.

It is also important to remember that if the recommended torque is not observed during tightening, problems can arise both with insufficient torque and with overtightening of the bolts. Increased clearance results in low oil pressure, knocking and wear. A reduced clearance will mean that in the mating area, for example, there is a strong bearing pressure on the neck, which interferes with the operation of the crankshaft and can cause it to wedged.

For this reason, tightening is done with a torque wrench and with a precisely defined torque. Do not forget that the tightening torque of the connecting rod and main bearing cap bolts is slightly different.

Read also

Why does the crankshaft liners turn: the main reasons. What to do if the connecting rod has cranked, how to properly change the connecting rod bearings.

Engine repair is considered the most difficult in a car, because no other part of it contains such a huge number of interconnected elements. On the one hand, this is very convenient, because in the event of a breakdown of one of them, there is no need to change the entire assembly, it is enough just to replace the failed part, on the other hand, the more components, the more complex the device and the more difficult it is to figure it out for someone who not very experienced in auto repair business. However, with a strong desire, everything is possible, especially if your zeal is supported by theoretical knowledge, for example, in the matter of determining the tightening torque of the main and connecting rod bearings. If, for now, this phrase is a set of incomprehensible words for you, be sure to read this article before getting into the engine.

Main and connecting rod bearings are two types of plain bearings. They are produced using the same technology and differ from each other only in the inner diameter (for connecting rod bearings, this diameter is smaller).

The main task of the liners is to convert translational movements (up and down) into rotational ones and ensure the smooth operation of the crankshaft so that it does not wear out ahead of time. It is for these purposes that the liners are installed under a strictly defined gap, in which a strictly specified oil pressure is maintained.

If this gap increases, the pressure of the engine oil in it becomes less, which means that the necks of the gas distribution mechanism, crankshaft, and other important components wear out much faster. Needless to say, too much pressure (reduced clearance) also does not carry anything positive, since it creates additional obstacles in the operation of the crankshaft, it can begin to wedge. That is why it is so important to control this gap, which is impossible without the use of a torque wrench in repair work, knowledge of the necessary parameters that are prescribed by the manufacturer in the technical literature on engine repair, as well as compliance with the tightening torque of the main and connecting rod bearings. By the way, the force (torque) of tightening the bolts of the connecting rod and main bearing caps is different.

Please note that the given standards are relevant only when using new sets of parts, since the assembly / disassembly of an assembly that was in operation due to its development cannot guarantee compliance with the necessary clearances. Alternatively, in this situation, when tightening the bolts, you can focus on the upper limit of the recommended torque, or you can use special repair inserts with four different sizes that differ from each other by 0.25 mm, provided that the crankshaft is ground until the minimum gap between rubbing elements will not be 0.025 / 0.05 / 0.075 / 0.1 / 0.125 (depending on the available clearance and the repair product used).

Examples of specific tightening torques for the bolts of the connecting rod and main bearing caps for some cars of the VAZ family.

Video.