Hex nut Strength class 5 | Hex nut Strength class 8 |
1 - Strength class 10.9
2 - Strength class 9.8
3 - Strength class 8.8
Property class marking for metric hex nuts
Hex nut Strength class 9 | Hex nut Strength class 10 |
The ends of metric studs are also marked according to their strength class. A digital code is applied to large studs, while smaller ones are marked in the form of geometric shapes.
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 American fasteners from metric fasteners is to measure the thread pitch, or compare the threads to the threads of a uniquely identified element.
It should be remembered that only small fasteners fall under the SAE classification. Larger items with non-metric threads are US 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, special attention should be paid to the compliance of the strength class of the installed new elements with the strength class removed.
Method 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 (under the tightening force of fasteners should be understood the torque applied to it). Overtightening the fastener can break the integrity of the fastener, while undertightening it leads to insecure coupling 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 allowable tightening forces, many of which, as already mentioned above, are given in the Specifications at the beginning of each Chapter. Strictly adhere to the recommendations given on the tightening forces of the fasteners used on the vehicle. For tightening fasteners not listed 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 screwed into steel or cast (not aluminum) detail.
Metric thread sizes
M6 | 9 – 12 Nm |
M8 | 19 - 28 Nm |
M10 | 38 - 54 Nm |
M12 | 68 - 96 Nm |
M14 | 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 |
SAE/USS 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 a component (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 text of the relevant Chapters of the Guide, as well as on Ref. illustrations. Unless a special procedure is specified, the following guidelines should be followed to avoid deformation of the component.
In the first step, all bolts/nuts must be finger-tight. Further, each of the fastener elements in turn reaches one more full turn, and the transition from one bolt / nut to another must be carried out in a diagonal order (criss-cross). Further, returning to the first element, you should repeat the procedure in the same order, tightening the fasteners another half turn. Continue the procedure, tightening each element now by a quarter of a turn in one go until all of them are tightened with the required force. When releasing fasteners, proceed in a similar manner, 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. Try to remember the characteristic external features of the assembly, if necessary, make landing marking of parts, the installation of which in place can be performed in an ambiguous way (e.g. a grooved thrust washer on a shaft, etc.). It's a good idea to place 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 disassembled component.
When giving fasteners, try to mark its original position on the assembly. Often, reinstalling fasteners and washers immediately after removing the corresponding part will avoid 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 appropriately labeled, or simply in separate labeled boxes. This approach is especially useful when working with components consisting of many small parts, such as a carburetor, alternator, valve train, instrument panel or decorative upholstery.
When disconnecting electrical contacts and connectors, attention should be paid to marking wires or harnesses using adhesive tape with a digital 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 other fluids and maintain high pressure / vacuum inside the assembly.
Often such gaskets are coated with a liquid or paste sealing compound before installation (sealant). Sometimes, over time, or under the influence of elevated temperatures or pressures, such a strong «sticking» mating surfaces to each other, that the dismemberment of parts becomes a difficult task. In many cases, successful disconnection «stuck» components is helped by tapping them from the outside along the perimeter of the joint 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 shock-sensitive components should not be tapped. When this type of problem occurs, always check that all fasteners have been removed first.
Avoid prying parts with a screwdriver or pry bar inserted into the joint area, as this can easily damage the mating surfaces, which will further lead to the development of leaks. If you avoid jerking «stuck» assembly elements fail, use a pen from the old mark for this purpose, but remember that all chips that have formed must be carefully removed both from the mating surfaces and from the internal cavities of the components of the dissected assembly.
After separation of the parts, their mating surfaces must be carefully cleaned using a scraper to remove traces of the old gasket material. Hardened fragments can be pre-softened with a rust converter or a special chemical composition. In this case, a piece of copper tube with a flattened and pointed end can be used as a scraper. Remains of some gaskets can easily be removed with a copper brush, however, regardless of the method used, the mating surfaces should be completely clean and dry as a result of processing. If for any reason the mating surface is damaged, fill the defects with gasket sealant before assembling the assembly. In most cases, you should use a non-curing (or not fully cured) sealant.
Hose Removal Tips
Attention! If your car is equipped with an air conditioning system, never disconnect any hoses from the system components until the path has been discharged at a service station by an air conditioning specialist.
The precautions to be taken when removing hoses are very similar to those for removing gaskets. Avoid damage to the surfaces of fittings and pipes on which the ends of the hoses are pulled, as this may cause the development of leaks. In particular, the latter requirement applies to the procedure for removing the radiator hoses. Due to the various chemical reactions taking place in the tract of the cooling system, it often occurs «sticking» rubber hoses to the surfaces of fittings and branch pipes. To remove the hose, first of all, loosen the clamp of its fastening. Then grab the hose near the clamp with tongs and begin to rotate it on the fitting / connecting pipe to the right and left. Continue in this manner until the hose is completely free, then remove the hose from the fitting. A small amount of silicone or other lubricant introduced into the gap between the fitting and the hose will save effort. Before installing the hose, lubricate the inner surface adjacent to the end, as well as the outer surface of the fitting with a solution of soapy water or a small amount of silicone grease.
As a last resort, or if it is absolutely necessary to replace the hose with a new one, the end of the 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 / connecting pipe with the blade.
If the hose clamp is damaged, replace it with a new one. Twist-type clamps usually weaken over time, so, regardless of condition, it is better to replace them with more practical screw or worm.