The crankshaft is steel, made by hot stamping. The shaft journals are hardened with high frequency heating

The crankshaft has four main bearings and three connecting rod journals.

The latter have internal cavities closed with plugs, where the oil undergoes additional centrifugal purification.

These cavities are connected by inclined channels with transverse channels in the main journals.

To balance the engine and unload the main bearings from the inertial forces of the reciprocating masses of the pistons and connecting rods and unbalanced centrifugal forces, counterweights are installed on the cheeks of the crankshaft, the assembly with which the shaft is balanced.

In addition, the balancing system includes two remote masses, one of which is made in the form of a tide on the flywheel, the other is a counterweight mounted on the front end of the crankshaft.

Axial fixation of the shaft is carried out by four bronze half rings installed in the undercuts of the rear main bearing.

To prevent rotation, the lower half rings with their grooves enter the pins pressed into the rear main bearing cover.

The toe and shank of the crankshaft are sealed with rubber self-clamping cuffs.

The crankshaft 2Z6NE-1005009 (marking 236N-1005015-U) is installed on the engines

The crankshaft is marked on the 5th cheek.

The main bearing shells of the crankshaft and the lower head of the connecting rod (Fig. 1) are replaceable, thin-walled, have a steel base and a working layer of lead bronze.

YaMZ diesel crankshaft bearing shells

The upper and lower crankshaft main bearing shells are not interchangeable. The top liner has a hole for oil supply and a groove for its distribution.

The connecting rod bearings are interchangeable.

On YaMZ-2Z6BE, YaMZ-236B, YaM3-2Z6NE and YaM3-236N engines, oil is supplied through the hole in the liner to the bushing of the upper head of the connecting rod and the piston pin.

Mounting the crankshaft to the engine

When installing the crankshaft on the engine, ensure that the dimensions of the bearing shells match the dimensions of the shaft journals.

Before installation, ensure that the external surfaces and internal cavities of the crankshaft and other mating surfaces are clean.

Lubricate the journals and running surfaces with clean engine oil.

To facilitate the installation of the flywheel in the correct position relative to the crankshaft, the number “6” is applied on the flywheel hub, which, during assembly, must be combined with the number “2” on the end of the crankshaft.

Main bearing caps are not interchangeable; when installing them, make sure that the stamp on the cover matches the stamp on the block.

Tighten the main bearing caps starting with the vertical bolts and tighten in two steps with a torque after retorque of 430 - 470 Nm (43 - 47 kgm), then tighten the horizontal bolts in two steps to a final tightening torque of 90 - 120 Nm (9 - 12 kgcm).

Before tightening the rear thrust main bearing, equalize the axial clearance, for which, after slightly tightening the bearing cover with bolts, move the crankshaft back and forth in the axial direction until it stops with a crowbar, first back, then forward, aligning the position of the cover.

After tightening the bolts, check the end play with a feeler gauge. It should be the same on both sides of the lid.

The crankshaft journals can be of two nominal sizes and therefore the following marking options and the use of the corresponding liners are possible.

How to repair a MAZ crankshaft

Note: The letters "H", "U", "Sh", "K" and the number "1" are branded when marking by impact.

Replacing the crankshaft gear

The crankshaft gear can be replaced without removing the crankshaft from the engine.

With the pulley and the front cover of the block removed, press the front counterweight and gear with a puller.

Before installing the gear and the front counterweight, heat up to a temperature of 105-155°C and sequentially press them in until they stop using a special tool.

Cleaning the crankpin cavities

Crankpin cavities of YaMZ crankshaft

Each time the crankshaft is removed from the engine to replace the liners, clean the cavities of the connecting rod journals, after removing the plugs 2 (Fig. 2), which close the cavities.

Replace the caps with new ones, they are not allowed to be reused.

Before installing the plugs, file down the swelling of the metal at the edges of the holes from the previous reaming, wash the shaft and blow out the oil channels.

Press the plugs to a depth of 5-6 mm from the edge of the hole, and then punch inside the hole at three points equally spaced around the circumference to prevent spontaneous pressing out of the plugs.

Basic requirements for grinding crankshaft journals

Grinding the crankshaft journals for repair dimensions should be carried out within the prescribed dimensions, while ensuring that the following requirements are met:

  • 1. When regrinding the shaft necks to repair dimensions, ensure a smooth transition radius of 6-0.5 mm from the necks to the cheeks without undercuts, burns, rough scratches; the roughness of the surfaces of the necks should not exceed 0.20 microns, the radii of fillets - 0.32 microns.
  • 2. The value of the radii of the axes of all cranks of the shaft must be 70 ± 0.12 mm.
  • 3. The parallelism tolerance of the axes of the middle main journals relative to the common axis of the extreme main journals should not exceed 0.010 mm, the tolerance of the parallelism of the axes of the connecting rod journals relative to the common axis of the extreme main journals should be no more than 0.03 mm over a length of 100 mm or 0.022 mm over the length of the neck.</ li>
  • 4. Ovality, taper, concavity and barrel-shaped main and connecting rod journals are not allowed more than 0.005 mm.
  • 5. Cracks on the shaft surface are not allowed. Check the absence of surface defects with a magnetic flaw detector with mandatory subsequent demagnetization.

When installing the crankshaft, it is necessary to ensure a diametrical clearance between the main journals of the crankshaft and the liners within 0.07-0.12 mm.

For this you need:

  • - check the conformity of the dimensions of the liners with the dimensions of the crankshaft journals.

The dimensions of the liners are checked by the marks that the manufacturer has on the outer surface of the liner;

Unscrew the bolts securing the main bearing caps and remove the caps.

Wipe the planes of the connector and the nest for the liners in the cylinder block and in the main bearing caps;

  • - remove the packaging from the set of main bearing shells and wipe them.

Install the upper bearings with hole and groove into the sockets located in the cylinder block, and the lower bearings into the main bearing caps, aligning the retaining locks with the grooves in the sockets.

  • - install the covers on the cylinder block, screw in the bolts by hand 1 - 2 threads and tighten them to a torque of 300 - 320 Nm (30 - 32 kgcm).

When tightening the bolts, lightly tap the cover with a rubber mallet;

  • - measure the diameters of the holes of the main bearings with an indicator caliper 100-160 mm, the diameters of the crankshaft journals with a micrometer 100-150 mm.

The difference in readings will give the clearance that will be after installing the crankshaft.

If the readings do not fit within the allowable diametral clearance, then it is necessary to select another crankshaft or select liners in thickness from the same size group.

After selecting the liners and the crankshaft, the main bearing caps are removed along the diametral clearance, having previously unscrewed the bolts.

Before installing the crankshaft in the cylinder block, it is necessary to clean the sharp edges of the lubrication holes with a scraper or a filled bar, wipe and lubricate the upper crankshaft bearing shells with diesel oil.

Installing YaMZ engine gears

When installing the crankshaft into the cylinder block, it is necessary to wipe the necks and align the “O” marks on the tooth of gear 3 of the crankshaft and the cavity of gear 4 of the camshaft (see Fig. 3).

Then, install the crankshaft thrust washers into the undercuts of the rear main bearing of the cylinder block so that the grooved side is adjacent to the thrust ends of the shaft.

The half-rings must first be wiped and lubricated with diesel oil.

After installing the shaft, it is necessary to lubricate its main journals with diesel oil.

When installing the crankshaft rear bearing cover, wipe the liners and install the thrust bearing half rings on the cover so that the grooved side is adjacent to the thrust ends of the shaft.

After that, the previously removed covers are installed, having previously wiped the liners.

Dress for pressing the oil deflector onto the rear end of the crankshaft

When installing the covers, it is necessary to observe the coincidence of the serial number of the cover with the serial number of the support on the cylinder block, while the stamped side of the cover must face the left row of cylinders.

The numbering of the supports on the block starts from the front end of the cylinder block.

The bolts are tightened with a torque wrench to a torque of 300-320 Nm (30-32 kgcm).

At the same time, the bolts of the intermediate supports and the front support are tightened, and the bolts of the crankshaft rear bearing cover are tightened after adjusting the clearance in the thrust bearing.

Wrench for tightening the YaMZ counterweight nut

The bolts are tightened sequentially in two stages (preliminary and final tightening), starting with the middle bolts and ending with the extreme ones.

The axial clearance is checked with a set of feelers by moving the crankshaft along the axis in both directions.

The gap should be within 0.08-0.23 mm.

It is necessary to check at two opposite points through 180°.

After tightening the rear main bearing mounting bolts to a torque of 300-320 Nm (30-32 kgcm), the gap fluctuation for one thrust half ring should not exceed 0.05 mm.

The gap on both sides of the cover must be the same.

After tightening the bolts, the crankshaft should turn easily without jamming from hand force applied to the flywheel locating pins.

The main bearing cap bolts are protected from unscrewing with safety wire.

Then, the rear oil deflector is installed and pressed with a mandrel (Fig. 4) onto the rear end of the crankshaft and locked by pressing the metal into four holes on the crankshaft.

The front oil deflector, the lock washer are installed on the front end of the crankshaft and the front counterweight fastening nut is screwed on by hand.

After that, the crankshaft is stopped from turning with a stop inserted into the counterweight hole, tighten the nut with a wrench (Fig. 5) to a torque of 180-320 Nm (18-32 kgcm) and lock it with a washer.