Instructions for tightening the cylinder head bolts

The next tightening of the cylinder head must be carried out during each routine repair or maintenance of the power unit (change of oil or consumables). It is mandatory to carry out the procedure after intervention in the internal combustion engine structure, and additional tightening after 500-700 kilometers. It is not recommended and there is no need to climb into the mechanism anymore. After full tightening, the bolts sit firmly in their sockets and do not loosen due to vibration. Otherwise, leaks or burnout of the cylinder head gasket may occur, which can lead to major repairs.

Modern motors manufactured after 2010 do not require periodic tightening of the studs due to the updating of the device and mechanism.

Purpose and structure of the cylinder head

The cylinder head is a kind of combustion chamber cover. To enable the internal combustion engine to operate, intake and exhaust valves, spark plug(s) and various sensors are located here (depending on the design of the engine).

A complex part on modern cars is made of aluminum and contains a complex system of valve actuators, oil and cooling channels.

What happens in the cylinder head while the engine is running

Without delving into the “wilds” of engine building, there are two main forces acting on the cylinder head.

1. Internal pressure of the combustion chamber. When the fuel ignites in the cylinder, an excess of forces is generated that turns the crankshaft. This force acts on all walls of the working chamber and the head as well.
2. Intense heating causes the part to turn inside out. Increased temperature inside the combustion chamber can damage the cylinder head.
3. Pressure inside lubrication and cooling lines. Inside the crankcase and cooling system there are pumps installed that supply fluid to the unit components.

Forces acting on the cylinder head during bolt tightening

The stable operation of the engine depends on the correct tightening of the bolts. When tightening the fastening elements, the part is subjected to strong pressure. In places where hairpins pass. Consequently, if you violate the sequence of actions, the head will be pulled and will have to be sharpened.

Working with a torque wrench

The dynamo key has a measuring scale that allows you to accurately determine the tightening force. Before use, a new key should be developed by making several tightenings at a minimum, due to which the parts of the mechanism will be lubricated. After use, the tool must be stored for storage, lubricated with a thin layer of machine oil. After each procedure, zero should be set (if a click key was used) so that subsequently the spring retains its elasticity and accuracy is maintained. With active use of the key, the spring still stretches, so it is recommended to calibrate it every year. When tightening, do not knock on the tool or use any extension cords.

If the motorist has a click-type key, then before tightening you need to select the required torque. To do this, unscrew the nut located at the bottom of the handle and set the desired value. After this, the nut is tightened. When tightening the cylinder head bolts, the key will click and begin to slip. This means that the required torque has been achieved.

Instructions for using a click key

The pointer tool does not allow you to set the tightening torque in advance, so the force will have to be controlled directly in the process. Tighten the fasteners carefully so as not to accidentally apply more force than necessary. It is better to indicate the required reading on the scale in advance. When twisted, the pointer remains stationary, and the handle with the scale moves.

An electronic dynamo key is similar to a click key, but the measurement is carried out using an electronic device. The moment is also set in advance. When it is reached, a beep sounds.

Mounting features

Regardless of the type of engine, the cylinder head is attached to the block using long studs. The fasteners are tightened in a certain sequence and with a large torque using a torque wrench. The use of the device is mandatory; the stability of the motor and the safety of the driver on the road depend on the accuracy of tightening.

Also, when installing the part, you should use a special gasket. The seal is made of materials that are resistant to pressure and elevated temperatures.

What forces act on the cylinder head during engine operation?

Any mode of motor operation leads to uneven heating of the head. The areas located above the combustion chambers heat up much more strongly than the rest of the body, which causes thermal stress on the metal. The higher the engine speed or the greater the load on it, the greater the difference in heating of different parts of this part. In some areas, the thermal expansion of the aluminum from which the body of this part is made is so strong that it increases the pressure on the gasket between the head and the cylinder block. Therefore, after a certain period of time it is necessary to repeat the tightening torque of the screws, otherwise there is a high probability of the gasket burning out.

What forces act on the cylinder head when tightening the screws?

The gasket, which is installed between the cylinder block and the cylinder head, has a certain thickness, which decreases during tightening. Despite its overall rigidity, the aluminum body of this part is deformed by thousandths of a millimeter during tightening, so it is necessary to carry it out from the center to the edges. In this case, it is possible to compensate for the bending of its surface (sole). When the head rests on the cylinder block, the pressure on each part of its sole is the same. As it is tightened, the pressure in the places where the bolts (screws) are installed increases, which leads to a V-shaped deformation of the sole. To avoid this, you must strictly follow the sequence of actions. If the tightening order is incorrect or the force (torque) does not match the motor, the likelihood of gasket burnout and engine repair increases.

Torque wrench and its types

It is needed to tighten the cylinder head bolts. In 2022, devices are divided into three main types.

Snap key

A fairly popular type of device, widely used due to its moderate cost and ease of operation.

The principle of operation is based on setting the required torque on the main and auxiliary scales. When the set force is reached, the ratchet and key are activated and slip with a characteristic sound.

Arrow key

The very first and simplest variety, preserved from USSR times in many workshops. The operating principle is based on the resistance of the torsion bar when the torque increases.

The main disadvantage is the low accuracy of the device - over time, the torsion bar wears out and the key begins to lie in a larger direction.

Digital key

Digital devices are characterized by increased measurement accuracy, which allows them to be used on advanced internal combustion engines that require careful calibration.

Such keys are still rare in 2022 and are found mainly in workshops, due to their high cost.

Other devices

In the absence of a special tool, you can use improvised materials such as a long lever and a regular cantor. The point is to calculate the standard formula.

For example, to obtain a tightening torque of 10 Nm, you should use a 1 meter long lever and apply a force of 1 kg to its end.

Tools used

The equipment you need is a torque wrench with force calibration for a specific car (on different cars, the tightening torque of fasteners can differ significantly), a socket head of the required size, which is suitable for a specific type of fastener.

So, torque wrenches come in several types:

• clicky;
• switch;
• digital;
• other devices.

Snap key

A click (also limit or spring) wrench is used to quickly tighten threaded connections with a given torque. When the required force is reached, a spring mechanism inside the key is activated, resulting in a click being heard, indicating the need to stop tightening with the current torque (force). The error of such a key does not exceed 4% (subject to correct storage and use).

Arrow key

An arrow (torsion) wrench is a lever with an arrow and a force scale (or a dial indicator), which makes it the easiest to use. When using such a wrench, the arrow indicates the current tightening torque when turning the lever. Among the disadvantages of such keys, it is worth noting a rather large error (from 5 to 20%), and over time the steel loses its elasticity, which makes it impossible to adjust it.

Digital key

The digital key (or digital adapter) is the most accurate tool in its category - its accuracy is only 1%. Therefore, such wrenches are often used when installing “critical” threaded connections.

Other devices

Homemade torque wrenches are used when there are no other devices at hand - usually these are homemade mechanisms consisting of a ratchet and old spring scales or modern digital ones. But the error of such devices is much higher than factory keys - this is due to incorrect force calibration.

Cylinder head bolt tightening torque

For the cylinder head of classic VAZ 2101-07 models, the nominal value is 8 kgf.m.
For other modifications, this moment is not suitable. As a sample, you can take the cylinder head of the Hyundai D4DD engine, where the recommended norm is 18 kgf.m. An important factor is the cleanliness of the operation. Before repairs, you need to clarify how many tightening bolts are designed for in a specific engine model. Some automakers make the elements disposable. This situation is justified by the risk of reuse - the bolts may simply not withstand the second application of load.

Next, before installation, it is imperative to remove all dirt, grease or dust residues from the threaded channels and the screws themselves. Otherwise, debris may clog the bottom of the well, which will prevent the part from being tightened completely.

Preparing the tightening surface of the block and head

The head is installed in its original place after partial or major repair of the engine units and components. Before installing the head, new liners are installed in the block, which are sealed with special rubber rings that prevent coolant from leaking out of the jacket. The installed sleeve protrudes with its upper edge above the plane of the block. Pistons and liners are selected according to one size group, and the connecting rods and pistons are additionally weighed. The permissible difference in weight should not exceed 30 g.

Preparation of the contracted surface of the block and head.

To connect the connecting rod and piston, the pin is pressed into the piston using a special mandrel, and then secured against longitudinal movement with locking rings. A correctly selected finger does not move in the mounting sockets under the influence of its own weight.

The skew of the pin in the hole of the connecting rod bearing, as well as bending or conical wear of the cylindrical element is not allowed.

Rings are installed in the grooves on the piston body to provide compression and remove traces of oil from the surface of the liner. MTZ naturally aspirated engines use 3 compression rings, supercharged engines are equipped with 2 rings, the top one is coated with a wear-resistant chromium-based alloy. The ring locks are placed at 180° intervals, providing increased compression. When installing parts, you need to pay attention to the marks indicating the correct location of the rings relative to the piston bottom.

Before installing the pistons, it is necessary to install the crankshaft in its original place (if it was dismantled for grinding from the replacement). Then a piston with a connecting rod is installed in the cylinder liner, after which the liners are mounted and the caps of the main and connecting rod bearings are tightened. To check the correct assembly, use a torque wrench to turn the engine shaft.

The standard force should not exceed 60 N/m; if there is increased resistance to rotation, it is necessary to find the cause of the malfunction.

Installing the gasket and cylinder head on the block

The gasket is placed on the upper surface of the block, previously wiped with a clean rag. It is first recommended to check the condition of the aligned planes of the block and head with a metal tool ruler. Warping of parts is not allowed, since curved surfaces do not provide uniform clamping of the gasket, which will be pierced by the flow of exhaust gases. Damaged planes are ground on a special machine, and a metallized gasket with an increased thickness of material is used to seal the joint.

Before installing the gasket, it is recommended to re-check the protrusion of the upper flange of the cylinder liners. On an atmospheric diesel engine, the permissible value is in the range of 0.065-0.165 mm, on a supercharged version - 0.05-0.11 mm. To ensure uniform installation of the liners after replacement, it is necessary to install the head housing on the block, which is pressed with standard bots. Metal spacer sleeves 100-105 mm long are placed under the heads of the fastening elements; the tightening torque does not exceed 10-15 N/m.

When connecting parts, a new gasket is used; using a previously used plate is strictly prohibited. The part is removed from the plastic bag; it is recommended to inspect the surface of the part and make sure there are no tears or dents. To improve the tightness and facilitate the removal of parts during future repairs, apply graphite heat-resistant paste to both sides of the gasket.

Then the cylinder head is placed on top of the gasket, bolts are inserted into the holes, which are then tightened with a torque wrench. To ensure the quality of the connection, it is necessary to use new bolts, since old parts are deformed during tightening and during diesel operation. A thin layer of engine oil is applied to the threaded part, and the bolts are screwed into the holes by hand.

Units of force applied

In European and CIS countries, it is customary to use Newtons multiplied by a meter. A universal unit of measurement is present on all instruments and torque wrenches. In Western Europe, the USA and Australia, Pounds*inch are used.

The “domestic” unit of measurement is more accurate, which confirms its spread.

Table of tightening torques for threaded connections

Among the most common cars, the following group stands out:

• KAMAZ;
• 8 valve Daewoo Nexia;
• Lada Granta;
• Hyundai Accent;
• Chevrolet Niva;
• Hino Ranger;
• UAZ Patriot;
• Toyota Rav-4.

These cars are considered the most popular guests of service stations, therefore, it is logical to make a list specifically based on the power units of the cars. The following is a table of torques for pulling cylinder head bolts of the most popular car models in Russia.

Basic recommendations

First of all, it should be noted that such a procedure can be carried out after repairing the power unit or in order to check the tightening torque of the bolts during engine operation. If the cylinder head has been dismantled, you should carefully inspect the bolts, as well as the holes in the cylinder block for their installation. Screws must not have elongation or deformation of the threaded part. The holes in the block for the bolts are cleaned of any remaining engine oil, liquid, or other foreign particles. If this is not done, the cylinder block may be damaged, and the cylinder head will not be able to be tightened with the required force.

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Work should begin only after reading the vehicle manufacturers' recommendations for operation and repair. There the driver will find all the necessary information to complete the job, including the forces and sequence of tightening the bolts.

Important! For engines with TTY bolts, there is a prohibition on reuse, as they may break.

Another feature of using such bolts is their installation at a certain angle. To do this, you will need a special key with an indicator that will show the degree of inclination.

User Igor Ivanov shows in the video the installation and tightening of the cylinder head.

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Bolt tightening torque (force)

The tightening torque for the bolts is different for each car (due to design features). Each vehicle has its own table of fastener tightening torques. In the next section, we will consider the cylinder head fastening forces using the example of a VAZ head.

Table: tightening torques for connections depending on thread diameter

Correct tightening order

There is a certain order for tightening the bolts; it is the same on almost all cars - from the center of the head to its edges, cross to cross. So, for example, the two central bolts of the right and left rows are tightened first, then the two bolts located to the left of the central ones, then the two to the right of the central ones, then the two bolts located on the left in both rows, and the bolts located on the right in both rows complete the order.

It is important to remember that fastening is always performed in three to four approaches:

1. The first approach is a force of 3-4 kgf.
2. The second approach is a force of 7 kgf.
3. The third approach is a force of 9 kgf.
4. The last approach is a force of 11.5 - 12 kgf.

Some nuances

The tightening torque is one of the main factors for the normal fit of the block head. But this criterion is influenced not only by the applied force, but also by the fasteners themselves:

• General condition of the bolts – new or used;
• Presence of lubricant on the threaded part;
• Thread condition.

The type of power plant (petrol, diesel), as well as the number of valves, does not affect the cylinder head tightening technology. But this does not mean that the force and tightening procedure are identical for all motors, and before seating the head, you should definitely study the conditions for performing the operation and all its features.

Errors when installing the head

If you do not use a torque wrench when installing the cylinder head, you may make a mistake with the force, which will lead to uneven torque. In such cases, there will be excessive or insufficient force, which will result in either deformation of the head surface or allow the breakthrough of gases, oil or coolant. In both cases, this is fraught with serious consequences for the engine.

If you follow the rules for tightening the fastening bolts, as well as the required torque, you can always count on reliable and durable operation of the installed parts. The gas distribution mechanism in the engine plays a major role, so you should not neglect the rules for installing the component elements.

Tightening procedure for cylinder head bolts

The standard tightening pattern starts from the central screws to the edges. This rule must be strictly adhered to in order to avoid distortion or cracking of the aluminum “motor head”.

Typically the sequence of actions for a four-cylinder model looks like this:

From the first number you need to follow further to the edges. The effect of deformation of the head and gasket will be minimized. The procedure is similar for six or five cylinder in-line internal combustion engines. In the case of a V-shaped block, the sequence is relevant with the allowance for the fact that two heads are used there.

The following motors can be classified as standard row engines:

• ZMZ 406/402;
• GAZ 53;
• D 260;
• K24Z3;
• YaMZ 236;
• D 240.

Since these units are similar in design, the general system is applicable to them. This category includes the Lada Priora with 8/16 valves Chery Tiggo, and the VAZ 2108. Only Japanese engines of Mazda cars, some Toyotas, Hondas and Mitsubishi raise doubts. Due to the high-tech, complex design, the sequence of actions may vary.

Working with a torque wrench

Extreme caution should be exercised when using DMC.
The tool is sensitive to mechanical damage - it’s easy to lose the calibration and the tool will become unusable. Depending on the type of key, the principle and sequence of operation differs.

Which method of tightening fasteners is better?

Each method of tightening cylinder head threaded connections has its own pros and cons. Using a torque wrench allows you to achieve accurate results without damaging parts and bolts that can cause engine failure. The second method - without a dynamo key - is widely used among people due to its simplicity, accessibility and the absence of the need to purchase an expensive key. Despite the fact that professional mechanics advise using only the first method, car manufacturers in technical manuals often advise using a combined method. Its essence lies in the fact that when tightening torques exceed 8–10 kg*m, there is a high probability of a 100% error, even with the use of lubricants, so the fasteners are first tightened with a dynamo key to the specified values, and then turned at an angle. In practice, this method turns out to be the most effective, since the bolt is tightened until there is a characteristic click, which guarantees full compliance with the moment of force.

One of the important parts of the engine is the cylinder head. Correct tightening of bolts, torque determination and work order ensure uninterrupted operation of the cylinder head and power unit of the vehicle.

How to tighten cylinder head bolts without a torque wrench

The price of a professional instrument with acceptable accuracy reaches $200, which is beyond the means of the average person. However, physics gives users the right to independently manufacture a “likeness” of this instrument for a reasonable fee.

For this you will need:

• standard key;
• lever (pipe or other object);
• tape measure or ruler;
• standard scales (canter).

To tighten bolts without a torque wrench, you need to remember a little physics. The tightening torque is the applied force to the meter lever (kgf.m). Therefore, you need to measure the length of the key and divide 1 by the resulting number. Next, the result is multiplied by the tightening torque and the answer will be the required indicator on the scales.

For example, you can simulate the situation:

• nut with a required force of 3 kgf*m;
• open-end wrench 25 cm long;
• scales with an indicator of up to 20 kg.

Total:

• 1/0,25=4;
• 4*3 = 12.

Thus, if you attach a scale to the key, you need to pull the hook with a force of 12 kg. If it is necessary to tighten a bolt marked in Newtons, the force is calculated using the standard ratio here too.

Tighten the bolts correctly

Any threaded connection is designed for a certain tightening torque. It is regulated by industry quality standards, for example, “OST 37.001.050–73 Tightening of threaded connections. Tightening standards" and guidelines from vehicle manufacturers.

Foreign manufacturers use other standards, but they are basically similar to domestic ones. The information below will be presented based on Russian standards.

To what extent?

Why is it important to maintain the correct tightening torque? Only proper tightening will ensure reliable fixation of the part, on the one hand, and prevent damage to the thread and/or the part itself, on the other hand.

Let's look at what happens when the tightening torque is exceeded using the example of a bolt and nut:

• Immediate thread deformation. Due to too much applied force, deformation and breakage of the threads on the part occurs. The bolt or nut is not subject to further use; in addition, certain difficulties will arise when trying to unscrew the nut for replacement. You will most likely need to use a drill or metal saw to cut off the nut.

• Damage to metal hidden from view. It may seem that the nut is tightened correctly, but due to exceeding the yield strength, irreversible changes occur in the bolt or nut: deformation, disruption of the metal crystal lattice. Such a case is especially dangerous because it is not immediately noticeable, but after some time a crack in the bolt can lead to dire consequences.

After passing the yield point, irreversible changes begin to occur in the metal of the sample, the crystal lattice of the metal is rearranged, and significant plastic deformations appear.

• The yield strength is a mechanical characteristic of a material that characterizes the stress at which strain continues to increase without increasing the load. Designation σт.
• Unit of measurement: Pascal or multiples.
• This is an important parameter with which permissible stresses for ductile materials are calculated.

If, on the contrary, you do not tighten the nut with the appropriate torque, after a while it will simply unscrew, which can also lead to undesirable consequences. Therefore, it is strongly recommended to tighten threaded connections not “with all your strength”, not by hand, but wisely, using special equipment.

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Features of the work performed using the example of some cars

In different cars, the procedure is performed according to the same scenario, but there are also nuances.

VAZ-2112 16 valves

On a 16 valve twelve, the head is secured with 10 bolts. Each element must be screwed in in a certain order in three steps.

1. The first pass is performed at 20 N*m.
2. Next, you need to tighten each screw 90 degrees.
3. After 20-30 minutes, you need to perform step No. 2 again.

VAZ-2107

On the seven, the principle of operation is slightly different.

In the first pass, all bolts except No. 11 are tightened with a force of 3.5 kgf/m. The second approach implies a force of 11 kgf/m. Only on the third pull is screw No. 11 tightened with an indicator on the key of 4 kilos.

"Samara", 10th family, Priora

In Samara, twisting occurs from the center in 4 steps, where you need to do a pull-up of 2, then 8 kg and then two more pull-ups of 90 degrees.

"Volga"

The standard Volga ZML 402 engine has 10 cylinder head mounting nuts. They need to be tightened in the specified sequence in two approaches with a torque of 42 and 85 kgf/m.

After the first 2-3 starts and 5000 km, the fastenings should be tightened.

Required Tools

• Click or ratchet. The most popular variety among car enthusiasts. Depending on the option - amateur or professional - the error varies: from 3 to 5%. With its help, bolts can be fixed with a force from 40 to 360 Nm.
• Switch. The most affordable option of all. It is easy to operate, but the measurement error is at least 10%, so it is not recommended for use on cylinder head mounts. The maximum tightening force is 280 Nm.
• Electronic. The measurement error is minimal, the reliability is high, the tightening force is determined in the range from 20 to 350 Nm. It’s easy to control the moment thanks to sound and light signals. Its only drawback is its high price.