In the process of running-in, intense wear of rubbing parts occurs, as a result of which the microroughness of the mating surfaces decreases, the contact area increases, the specific loads decrease, the wear rate slows down and turns into normal wear. The period of normal wear is characterized by a relatively small growth rate of the gap in the interface, however, when a certain gap is reached, the wear rate increases sharply, which indicates the beginning of a period of critical wear. Operation of the unit with critical wear leads to malfunctions that most often cannot be restored. During operation, it is very important to repair the unit before critical wear occurs, while the repair costs will be significantly lower than when repairing a unit with critical wear.
Before making a decision on repair, it is necessary to diagnose the state of pairing in the units. As a rule, diagnostics are carried out according to indirect signs, such as increased noise, vibration, oil consumption, crankcase gas breakthrough, power loss, etc. For better diagnostics, the unit must be disassembled, the parts washed, inspected and subjected to appropriate measurements. Based on the results of inspection and measurements, a decision is made to continue operation without repair or a repair is determined. In this case, one should be guided by the following considerations: if the actual dimensions of the parts are within the tolerance fields permitted by this Manual, then the continued operation of the unit without repair is possible; if the dimensions are out of tolerance, then repair is necessary. The expansion of the tolerance fields given in this Guide should be regarded as the possibility of using the residual resource of the node without restoring the pairing. In the case of repair of the unit during the restoration of interfaces, the extension of the tolerance fields beyond the established ones is not allowed. The repair technology is usually divided into four stages of work:
- disassembly - washing;
- control - sorting;
- repair itself: restoration of the micro- and macrogeometry of the surfaces of the part and its physical and mechanical properties;
- assembly with preliminary control of parts entering the work.
Dismantling and washing operations are carried out in several stages: external washing of the unit, partial disassembly, nodal washing, disassembly into parts, washing and cleaning of parts. Before control-sorting, all parts must be thoroughly cleaned of dirt and carbon deposits, degreased, washed and dried (compressed dry air). Clean oil channels and holes in parts, flush under pressure and blow with compressed air.
Parts made of aluminum and zinc alloys are not allowed to be washed in alkaline solutions used for washing steel and cast iron parts, since aluminum and zinc dissolve in alkalis.
In the process of checking parts, breaks, cracks, dents, shells and other damages should be detected by external inspection. In critical parts, check for cracks using a flaw detector. The dimensions of parts must be controlled in places of greatest wear. Gear teeth wear out unevenly, so when checking them, at least three teeth located at an angle of 120°should be measured.
In view of the need to guarantee the operation of gears during the entire overhaul run, chips on the teeth and chipping of the working surface of the teeth of a fatigue nature are not allowed.
Assembly units such as connecting rod with connecting rod cap, cylinder block with main bearing caps, gearbox and final drive gears must not be dismantled. It is possible to dismantle the remaining assembly units, but if a decision is made to continue the operation of the mating elements without repair, then it is not advisable to dismantle them.
In all cases of repair by welding and surfacing, the weld should not have slag inclusions, unwelded areas, undercuts and other defects. Clean the seam after welding. Eliminate metal sags so that they do not interfere with the installation of mating parts.
Holes with worn or damaged threads are restored by threading an increased repair size or welding holes, followed by threading of a nominal size, as well as installing screw drivers and spiral threaded inserts. The use of threaded inserts is preferable for reasons of restoration quality and labor costs. Parts submitted for assembly must be clean and dry. Disposable self-locking threaded fasteners must be replaced with new ones. If it is impossible to use new self-locking parts when installing the old ones, they must first be blocked from turning away.
When assembling, install new gaskets and seals. The rubbing surfaces of parts during assembly must be lubricated with clean oil. When installing rubber cuffs, their working surface should be lubricated to avoid damage during installation. When installing cuffs with a metal case, the cuff socket should be lubricated with a thin layer of sealant.
Assemble units and assemblies in accordance with this Manual. Using a measuring tool, check the dimensions of the parts forming the fit before assembly.
When assembling parts that have a movable fit in mating, their free relative movement without jamming should be ensured. Install bushings, rings of ball and roller bearings using mandrels. When pressing bearings, force must not be transmitted through balls or rollers. Pressing tools must rest against the pressed ring. The pressing force must be aligned with the bearing axis to avoid misalignment of the rings.
If, according to the assembly conditions, the installation of critical parts is carried out by hitting a hammer, it is necessary to use mandrels and hammers made of non-ferrous metals, plastics, rubber, as well as fixtures and gaskets for pressing parts.
The keys must be firmly seated in the keyways of the shafts using a hammer or a non-ferrous mandrel. Play of the keys in the grooves of the shafts is not allowed.
The studs must be screwed into the threaded holes tightly, without play. Details should be put on the studs freely. The fastening of a unit or part with several nuts or bolts should be carried out evenly around the perimeter - first preliminary, and then finally. All nuts or bolts of connections must be tightened to the same torque. In all cases provided for by the Manual, it is necessary to use wrenches that allow limiting the tightening torque.
The list below includes the minimum standard tool required to perform operations for the removal, disassembly, repair, assembly and installation of vehicle components and assemblies:
- combination wrench set (1/4" — 1", 6—19 mm);
- set of interchangeable socket heads (1/4" — 1", 6—19 mm);
- ratchet reversible drive with crank (250 mm) («ratchet»);
- universal cardan type joint for socket heads;
- torque wrench;
- locksmith's hammer (250 - 300 g);
- mallet (wood, rubber or plastic);
- set of wrenches;
- set of external socket wrenches;
- candle key;
- a device for adjusting the candle gap;
- a set of measuring probes;
- wrench for bleeding the brakes;
- various screwdrivers;
- combined pliers;
- clamping pliers;
- dielectric pliers;
- pliers-platypuses;
- chisel (13 mm);
- hacksaw for metal with a set of blades;
- a set of files;
- tire pressure gauge;
- grease gun;
- non-ferrous metal scraper;
- wrench for removing the oil filter;
- locksmith's scriber;
- punch;
- beards (1.6; 3.3; 4.8mm);
- steel ruler-bar;
- a set of props;
- jack;
- electric drill 3/8" (9 mm) and a set of drills;
- fine sandpaper;
- wire brush (big and small);
- oil container;
- container for antifreeze;
- filling funnel.
For high-quality repair operations, it is also necessary to have special tools and devices:
- for compressing valve springs;
- for cleaning the grooves of piston rings;
- for compression of piston rings;
- for removal/installation of piston rings;
- for centering the clutch disc;
- to remove the steering wheel damper;
- for removing the caps of the springs of the brake pads;
- compressometer;
- countersink and hone for processing the edge and mirror of the cylinder;
- hone for processing the mirror of the brake cylinder;
- cylinder diameter gauge (caliper);
- a set of micrometers and a caliper;
- device for removing hydraulic pushers;
- universal puller;
- ball joint puller;
- impact screwdriver;
- stroboscope with adapter;
- manual combination pump (vacuum/pressure);
- tachometer;
- tester;
- a set of taps;
- lifting rigging;
- tools for dismantling brake springs;
- floor jack.