Before making a decision to repair, it is necessary to diagnose the state of the pairing of the units. As a rule, diagnostics are carried out according to indirect signs such as: increased noise, vibrations, oil consumption, breakthrough of crankcase gases, etc. For better diagnostics, the unit must be disassembled, the parts washed, inspected and subjected to micrometering. Based on the results of the inspection and micrometering, a decision is made to continue operation without repair or to carry out repairs. 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 it is possible to continue the operation of the unit without repair, if the dimensions are outside the permissible tolerance fields, then repair is necessary. The extensions of the tolerance fields given in this Guide should be understood as the possibility of using the residual resource of the node without restoring mates. In the case of repair of the unit during the restoration of interfaces, the expansion of tolerance fields in excess of the nominal ones is not allowed.
The repair technology is usually divided into four main stages of work:
- 1. Dismantling-washing.
- 2. Control-sorting.
- 3. Actually repair: restoration of micro and macro geometry of the surfaces of parts and physical and mechanical properties.
- 4. Assembly with preliminary control of the parts coming to the assembly.
Dismantling and washing operations are carried out in several stages: external washing of the unit, sub-dismantling, nodal washing, disassembly into parts, washing and cleaning of parts. Before control-sorting, thoroughly clean all parts from dirt and carbon deposits, degrease, rinse and dry.
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 damage are detected by external inspection. In critical parts, the presence of cracks is checked using a flaw detector. The dimensions of the parts must be controlled in places of greatest wear. The gear teeth wear unevenly, therefore, when checking them, at least three teeth should be measured, located approximately at an angle of 120°. In view of the need to guarantee the operation of gears during the entire overhaul run, spalling 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. The remaining assembly units can be dismantled, 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 of parts by welding and surfacing, the weld should not have slag inclusions, unverified 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 cutting threads of an increased repair size, welding holes, followed by threading of nominal size, setting screws and spiral threaded inserts. The use of threaded inserts is preferable for reasons of restoration quality and labor costs.
The insert is a springy spiral made of rhombic wire. At one end of the spiral, a technological leash is bent, by means of which the insert is wrapped into a previously prepared hole.
The technological process of repairing a threaded hole using a spiral insert includes the following operations: drilling a defective hole to a certain size, cutting a thread in it corresponding to the size of the spiral insert, screwing in the spiral insert and breaking off the technological driver along the notch.
The table shows the hole sizes and threads for spiral inserts used in the repair of automotive parts.
Drill and Tap Size Chart for Spiral Inserts
| Rated thread | Drill diameter, mm | Thread for spiral insert |
| M5 0.8 | 5,2 | M6 0.8 |
| M6 1.0 | 7,0 | M8 1.0 |
| M8 1.25 | 8,7 | M10 1.25 |
| M10 1.5 | 10,5 | M12 1.5 |
| M11 1.0 | 12 | M13 1.0 |
| M12 1.75 | 12,2 | M14 1.75 |
| M12 1.5 | 12.5 | M14 1.5 |
| M14 1.25 | 14.7 | M16 1.25 |
| M14 1.5 | 14,7 | M16 1.5 |
| M16 1.5 | 16,5 | M18 1.5 |
| M18 1.5 | 18,1 | M20 1.5 |
| M20 1.5 | 20,5 | M22 1.5 |
To repair threaded holes with spiral inserts, a special kit is produced, which includes: inserts, drills, special taps, wrenches for screwing inserts, barbs for cutting down a technological leash.
Parts submitted for assembly must be clean and dry.
Threaded connections must be undamaged. Disposable self-locking threaded fasteners must be replaced with new ones. If it is not possible to use new self-locking parts, when installing the old ones, it is necessary to additionally lock them from turning away.
When assembling, install new gaskets and seals. During assembly, lubricate the rubbing surfaces of the parts with clean oil. When installing rubber seals, lubricate the working surface of the cuff to avoid damage during installation. When installing oil seals with a metal case, lubricate the socket under the oil seal 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 assembling.
When assembling parts that have a movable fit in mating, their free relative movement, without jamming, must 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 ring to be pressed. The pressing force must match the axis of the bearing 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 devices 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. Bending of the studs when installing parts on them is not allowed, the fastening of the assembly 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 the same joint must be tightened to the same torque.
In all cases provided by the manual, it is necessary to use keys that allow you to limit the torque.
Visitor comments