Repair of the crankshaft consists in regrinding the main and connecting rod journals to the next repair size
The repair dimensions of the connecting rod and main journals are determined by the sizes of the sets of connecting rod and main bearings supplied as spare parts, which are given in table. 2. Tolerances of the main parts of the UAZ-3151 engine
The radial clearances in the crankshaft connecting rod and main bearings should be 0.020–0.049 mm and 0.020–0.066 mm, respectively.
Regrind the necks with a tolerance of 0.013 mm.
If the sizes of the connecting rod and main journals do not match, they must be reground to the same repair size.
The chamfers and holes of the front and rear ends of the crankshaft are not suitable for installation in a grinding machine. To do this, make removable centers-glasses.
Press the front center onto a neck with a diameter of 38 mm, and center the rear center along the outer diameter of the flange (Ж122 mm) of the shaft and fasten it with bolts.
When making adapters, make sure that the center and mounting holes are concentric.
Not observing this condition, it is impossible to ensure the necessary concentricity of the flywheel and gear seats to the axes of the main journals.
When grinding the connecting rod journals, install the shaft along additional centers, coaxial with the axes of the connecting rod journals.
To do this, you can use the center-cups, providing them with flanges with two additional center holes spaced from the middle hole by 46 ± 0.05 mm.
For the front end, it is better to make a new center flange, which is mounted on a neck with a diameter of 40 mm (on a key) and additionally secured with a bolt (ratchet) screwed into the threaded hole.
Before grinding the necks, deepen the chamfers on the edges of the oil channels so that their width after removing the entire grinding allowance is 0.8–1.2 mm.
Do this with a 60-90° point angled emery stone rotated by an electric drill.
When grinding the connecting rod journals, do not touch the side surfaces of the journals with the grinding wheel so as not to disturb the axial clearance of the connecting rods.
Keep the transition radius to the side surface at 3.5 mm.
Grinding with plenty of emulsion cooling.
While sanding, keep:
1. The distance between the axes of the main and connecting rod journals is 46 ± 0.05 mm.
2. Cone-shaped, barrel-shaped, saddle-shaped, oval and faceted necks are not more than 0.005 mm.
3. Angular arrangement of connecting rod journals ±0°10'.
4. Non-parallelism of the axes of the connecting rod journals with the axis of the main journals is not more than 0.012 mm over the entire length of the connecting rod journal.
5. The runout (when the shaft is installed with extreme main journals on prisms) of the middle main journals is not more than 0.02 mm, the neck under the timing gear is up to 0.03 mm, and the necks under the pulley hub and the rear oil seal are up to 0.04 mm.
After grinding the journals, flush the crankshaft and clean the oil channels from abrasive and resinous deposits.
Turn out the plugs of the dirt traps.
After cleaning the dirt traps and channels, screw the plugs back in place and seal each of them from spontaneous turning out.
Clean the oil channels also during maintenance repairs of the engine, when the crankshaft is removed from the block.
Fig. 1. Setting the clutch by labels: 1 - labels
After the repair, assemble the crankshaft with the same flywheel and clutch that were before the repair.
Install the clutch on the flywheel according to the factory marks "O" applied on both parts one against the other near one of the bolts securing the clutch housing to the flywheel (Fig.1).
Before installing on the engine, dynamically balance the crankshaft with clutch assembly on a special machine.
Pre-center the clutch disc using the gearbox shaft or a special mandrel.
Remove the imbalance by drilling the metal in the flywheel rim at a radius of 158 mm with a drill with a diameter of 12 mm.
Drilling depth should not exceed 12 mm. Permissible imbalance - no more than 70 gsm.
Replacing the shells of the main and connecting rod bearings of the crankshaft
Spare parts are supplied with liners for main and connecting rod bearings of nominal and seven repair sizes, which are given in table. 2. Tolerances of the main parts of the UAZ-3151 engine
Repair size inserts differ from nominal size inserts with an inner diameter reduced by 0.05; 0.25; 0.50; 0.75; 1.0; 1.25 and 1.50 mm.
Inserts replace main and connecting rod bearings without any adjustment.
Depending on the wear of the necks, when changing the liners for the first time, use the liners of the nominal or, in extreme cases, the first repair size (reduced by 0.05 mm).
Install liners of the second and subsequent repair sizes in the engine only after regrinding the crankshaft journals.
If, as a result of repeated grinding, the diameters of the crankshaft journals are reduced so much that the liners of the last repair size are unsuitable for it, then assemble the engine with a new shaft.
The radial clearance in the connecting rod and main bearings of the crankshaft should be 0.020–0.049 mm and 0.020–0.066 mm, respectively.
Check the size of the radial gaps using a set of control probes made of copper foil 0.025 thick; 0.05; 0.075 and 0.1 mm, cut into strips 6-7 mm wide and slightly less than the width of the insert.
The edges of the probes must be cleaned to prevent damage to the surface of the liner.
Check the radial clearance in the following order:
1. Remove the cover with the insert from the neck to be checked and place a pre-lubricated 0.025 mm thick control probe across the insert.
2. Replace the cover with the insert and tighten with bolts, while the bolts of the remaining covers must be loosened.
3. Turn the crankshaft by hand at an angle of no more than 60–90 °, in order to avoid damaging the surface of the liner with a feeler gauge.
If the shaft turns too easily, then the gap is greater than 0.025 mm. In this case, repeat the test with probes 0.05; 0.075 mm etc. until it becomes impossible to turn the crankshaft.
The thickness of the probe, at which the shaft rotates with a noticeable force, is considered equal to the actual gap between the bearing and the crankshaft journal.
When replacing earbuds please observe the following:
1. Replace the liners without adjusting operations.
2. Make sure that the locking protrusions at the joints of the liners freely (from the effort of the hand) enter the grooves in the shaft beds.
3. At the same time as changing the bearings, clean the dirt traps in the crankpins.
The connecting rod bearings can be replaced without removing the engine from the vehicle chassis.
Replace the main bearings with the engine removed from the vehicle chassis.
After replacing the liners, break in the engine as instructed in "Breaking in the Engine After Repair".
If, when replacing the liners, the engine was not removed from the car, then during the first 1000 km of run the speed should not exceed 50 km / h.
Fig. 2. Front end of the crankshaft
At the same time as replacing the liners, check the axial clearance in the crankshaft thrust bearing, which should be 0.075–0.175 mm.
If the axial clearance is more than 0.175 mm, replace washers 7 (fig. 2) and 8 with new ones.
The front washer is available in four thicknesses:
Fig. 3. Checking the axial clearance of the crankshaft
To check the clearance in the thrust bearing, place a screwdriver (fig. 3) between the first crank of the shaft and the front wall of the block and press the shaft towards the rear end of the motor.
Then, use a feeler gauge to determine the clearance between the end face of the thrust bearing rear washer and the shoulder plane of the first main journal.
Before installing the liners, check the alignment of the crankshaft main journals (deflection arrow).
To do this, install the crankshaft in the centers and check the position of the axes of the main journals according to the indicator.
Fig. 4. Rear end of the crankshaft
The front and rear ends of the crankshaft are sealed with oil seals (fig. 2 and 4).