Fasteners
Fasteners are nuts, bolts, studs and screws that are used to connect two or more parts together. There are a few things to keep in mind when working with fasteners. In almost any fastener, one or another type of locking and locking devices is used. These can be lock washers, locknuts, lock flags, or thread locking compound. All threaded fasteners used must be absolutely clean and straight, with undisturbed threads and non-rounded corners of the hex heads on which the wrench is put on. It should be a rule to replace damaged nuts and bolts with new ones. Special self-locking nuts with nylon or fiber inserts cannot be reused, as they lose their locking properties when released and must always be replaced with new ones during assembly.
Rusted bolts and nuts must be treated with a special penetrating compound before loosening and to avoid damage. Many mechanics prefer to use turpentine for this purpose, which is conveniently applied from a special small canister with a long spout. After wetting "stuck" fasteners with a penetrating composition, before proceeding with its release, the composition should be thoroughly impregnated with an oxidized contact layer for several minutes. Heavily rusted fasteners can be cut down with a chisel, cut down with a hacksaw or removed using a special wrench.
When cutting off a bolt head or breaking off a stud on an assembly, the rest of the threaded part can be drilled out or removed using a special tool. Most bodyshops can take on this as well as others (e.g. repairing stripped threads in threaded holes), repair procedures.
The flat washers and lock washers must always be reinstalled in the same order and in the same way as before when reassembling. Always replace damaged washers with new ones. Between lock washer and soft metal surface (e.g. aluminum), thin sheet metal or plastic, flat washers should always be installed.
Fastener dimensions
For many reasons, automotive manufacturers are increasingly adopting metric fasteners. However, it is important to know the difference between the sometimes used standard (also called American, or SAE standard) and more universal in the system of measures with metric fasteners, since, despite the external similarity, they are not interchangeable.
All bolts, both standard and metric, are classified by diameter, thread pitch and length. For example, a standard 1/2 - 13 * 1 bolt is half an inch in diameter, 13 threads per inch, and 1 inch long. Metric bolt M12 - 1.75 * 25 has a diameter of 12 mm, thread pitch 1.75 mm (distance between adjacent turns) and length 25 mm. Both bolts are externally almost identical, but are not interchangeable.
In addition to the features listed, both metric and standard bolts can be identified by looking at the head. To begin with, the distance between the flats of the head of a metric bolt is measured in mm, while for a standard bolt it is in inches (the same is true for nuts). As a consequence, a standard wrench is not suitable for use with metric fasteners, and vice versa. In addition, the heads of most standard bolts usually have radial notches that determine the maximum allowable tightening torque of the bolt (degree of strength). The more notches, the higher the allowable force (on cars, bolts with a degree of strength from 0 to 5 are usually used). The strength class of metric bolts is determined by a numerical code. Code numbers are usually cast, as for standard ones, on the bolt head (on vehicles, bolts of strength classes 8.8, 9.8, and 10.9 are usually used).
Also, according to the marks of the strength class, standard nuts can be distinguished from metric ones. To identify the strength of standard nuts, dot marks are used, stamped on one of the end surfaces of the nut, while the marking of metric nuts is again done using numbers. The greater the number of points, or the higher the value of the digital code, the higher the allowable tightening torque of the nut.
The ends of metric studs are also marked according to their strength class. Large studs are marked with a digital code, while smaller ones are marked in the form of a geometric figure.
It should be noted that a significant part of the fasteners, especially the strength class from 0 to 2, is not marked at all. In this case, the only way to distinguish a standard fastener from a metric fastener is to measure the thread pitch, or compare the thread with a uniquely identified one.
Standard fasteners are also often referred to as SAE fasteners, as opposed to metric fasteners, however, it should be remembered that only small fasteners fall under the SAE classification. Large fasteners with non-metric threads are American standard fasteners (USS).
Since fasteners of the same geometric size (both standard and metric) may have different strength classes, when replacing bolts, nuts and studs on a car, attention should be paid to the conformity of the strength class of the new fastener being installed with the strength class of the old one.
Bolt grade marking
above - standard / SAE / USS,
bottom - metric
Strength class marking for standard hex nuts
Strength class 5 | Strength class 8 |
Property class marking for metric hex nuts
Strength class 9 | Strength class 10 |
Strength class marking for metric studs
Dimensions/marking of strength class standard (SAE and USS) bolts
G - Strength class marking
L - Length (in inches)
T - Thread Pitch (number of threads per inch)
D - Nominal diameter (in inches)
Dimensions/marking of the property class of metric bolts
P - Strength class
L - Length (in mm)
T - Thread Pitch (distance between adjacent turns in mm)
D - Nominal diameter (in mm)
Procedure and procedure for tightening threaded connections
The tightening of most threaded connections should be done with the forces determined by the requirements of the Specifications given at the beginning of each Chapter of this Manual (fastener tightening force is understood as the torque applied to it when tightening). Below, the tightening force will also be referred to as the fastener tightening torque. Over-tightening the fastener may break the integrity of the fastener, while under-tightening it leads to insecure connection of the mating components. Bolts, screws and studs, depending on the material from which they are made and the diameter of the threaded part, usually have strictly defined permissible tightening torques, many of which, as already mentioned above, are given in the Specifications at the beginning of each Chapter. Strictly adhere to the recommendations given for the tightening torques of the fasteners used on the vehicle. For tightening fasteners not mentioned in the Specifications, use the torque chart below. The values given in the table are based on fasteners of strength classes 2 and 3 (Higher grade fasteners allow for more tightening), in addition, it is understood that the tightening of the dry (with unlubricated thread) fasteners in steel or cast (not aluminum) detail.
Metric thread sizes
M - 6 | 9 - 12 Nm |
M - 8 | 19 - 28 Nm |
M - 10 | 38 - 54 Nm |
M - 12 | 68 - 96 Nm |
M - 14 | 109 - 154 Nm |
Pipe thread sizes
1/8 | 7 - 10 Nm |
1/4 | 17 - 24 Nm |
3/8 | 30 - 44 Nm |
1/2 | 34 - 47 Nm |
American standard thread sizes
1/4 - 20 | 9 - 12 Nm |
5/16 - 18 | 17 - 24 Nm |
5/16 – 24 | 19 - 27 Nm |
3/8 - 16 | 30 - 43 Nm |
3/8 - 24 | 37 - 51 Nm |
7/16 - 24 | 55 - 74 Nm |
7/16 - 20 | 55 - 81 Nm |
1/2 - 13 | 75 - 108 Nm |
Fasteners located around the perimeter of any part (such as cylinder head bolts, oil pan and various covers), in order to avoid deformation of the part, it must be given and tightened in a strictly defined order. The procedure for tightening and retracting such fasteners is given in the relevant Chapters of the Guide. Unless a special procedure is specified, the following procedure should be followed to avoid distortion of the component. In the first stage, all bolts or nuts must be finger-tight. Further, each of them in turn must be tightened for another full turn, and the transition from one bolt / nut to another must be carried out in a diagonal order (criss-cross). Then, returning to the first bolt / nut, you should repeat the procedure in the same order, tightening the fasteners another half turn. Continue in the same manner, tightening each bolt/nut this time a quarter of a turn at a time until they are all tight. When giving away fasteners, you should also follow the described procedure, but in reverse order.
Disassembly of components
The disassembly of all components must be carried out in such a manner that during assembly each part can be installed in its original place and in the correct way. Remember the characteristic features of the appearance, if necessary, make landing marking of parts that can be installed in place in an ambiguous way (such elements include, for example, a thrust washer fitted with a groove on the shaft). It's a good idea to arrange the removed parts on a clean work surface in the order in which they were removed. It will also be useful to draw up simple schematic sketches or take step-by-step photographs of the component to be dismantled.
When removing a fastener, try to mark its original position on the assembly. Often, immediately reinstalling fasteners and washers after removal of the corresponding part avoids confusion during assembly. If this is not possible, all fasteners should be placed in a box specially prepared for this purpose, divided into sections and marked accordingly, or simply in separate marked boxes. This course of action is especially useful when dealing with components that consist of many small parts, such as a carburetor, alternator, valve train, instrument panel, or trim elements.
When disconnecting electrical contacts and connectors, attention should be paid to marking wires or harnesses using insulating tape with a numerical or letter code applied to it.
Sealing surfaces
On all vehicles, gaskets are used to seal the junction of the mating surfaces of two or more parts and serve to prevent leakage of oils and fluids and maintain high pressure or vacuum inside the assembly.
Often these gaskets are coated with a liquid or paste sealing compound prior to installation. Often, under the influence of time, temperatures or pressure, such a strong "sticking" to each other mating surfaces that the separation of parts becomes a difficult task. In many cases, the dismantling of such assemblies is helped by tapping them from the outside along the perimeter of the junction with a soft-faced hammer. You can also use an ordinary hammer for this purpose, striking through a wooden or plastic spacer. Cast housings and fragile components should not be tapped. When this kind of problem occurs, always check that all fasteners have been removed first.
Avoid using a screwdriver or pry bar to separate parts by inserting them between the mating surfaces, as the sealing surfaces can easily be damaged, which can cause leaks in the future. If jerking "stuck" assembly elements cannot be avoided, use a pen from the old mark for this purpose, but remember that after that all the chips that have formed must be carefully removed from the mating surfaces and from the inside of the assembly.
After separating the parts, their mating surfaces must be carefully cleaned, scraping off traces of the old gasket material. Hardened fragments of the old gasket can be pre-softened with a rust converter or a special chemical composition, and then removed from the mating surface with a scraper. In this case, a piece of copper tube with a flattened and pointed end can be used as a scraper. The use of copper tubing for this purpose is recommended, since copper is usually softer than materials used in a car, which reduces the risk of damage to the mating surface. Some gaskets can be easily removed with a copper brush, however, regardless of the method used, the mating surfaces should be completely clean and smooth. If for any reason the mating surface is scratched, fill the scratch with gasket sealant before assembling the components. In most cases, you should use a non-curing (or semi-hardening) sealant.
Hose Removal Tips
Attention! If your vehicle is equipped with an air conditioning system, never disconnect any hoses from the air conditioning components until the system has been discharged by a representative office of the company or an air conditioning specialist of a car service workshop
The precautions to be taken when removing hoses are very similar to those when removing gaskets. Avoid damage to the surfaces of the fittings and pipes on which the hoses are put on, as this can cause leaks. In particular, this applies to the procedure for removing the radiator hoses. Due to various chemical reactions, "sticking" rubber hoses to the mating surfaces of fittings and branch pipes. To remove the hose, first of all, loosen the clamp securing it to the fitting. Then grab the hose close to the clamp with tongs with a sliding joint and begin to rotate it on the fitting / connecting pipe from right to left. Continue this procedure until the hose is completely free, then remove the hose from the fitting. A small amount of silicone or other lubricant will make the procedure easier if it can be injected into the gap between the fitting and the hose. To facilitate the installation of the hose, grease the inside of the hose and the outside of the fitting.
As a last resort, or if it is absolutely necessary to replace the hose with a new one, the end of the removal hose put on the fitting can be cut with a knife and then separated from the surface of the fitting. At the same time, try not to damage the metal of the fitting / under the connecting pipe with a knife.
If the hose clamp is damaged, replace it with a new one. Twist-type clamps tend to loosen over time, so regardless of their condition, it is best to replace them with screw-type clamps on occasion.