Before assembling the engine, it is necessary to clean all its parts from carbon deposits and resinous deposits

It is impossible to wash parts made of aluminum alloys (cylinder block and head, pistons, etc.) in alkaline solutions, as these solutions corrode aluminum.

The following solutions are recommended for cleaning parts from carbon deposits:

For aluminum parts:

  • Soda (Na2CO3) - 18.5g
  • Soap (green or laundry) - 10.0 g
  • Liquid glass - 8.5 g
  • Water - 1 l

For steel parts:

  • Caustic soda (NaOH) - 25.0 g
  • Soda (Na2CO3) - 33.0
  • Soap (green or laundry) - 8.5g
  • Liquid glass - 1.5 g
  • Water - 1L

When assembling the engine, observe the following conditions:

  • - wipe all parts before assembly with a clean cloth and blow with compressed air, and lubricate all rubbing surfaces with clean oil;
  • - inspect the parts before putting them in place (for cracks, chips, nicks in other defects), check the reliability of the fit of the parts pressed into it, defective parts must be repaired or replaced with new ones;
  • - all threaded parts (studs, plugs, fittings), if they were turned out or replaced during the repair process, must be placed on minium or whitewash diluted on natural drying oil.

All permanent connections, such as cylinder block plugs, etc., must be placed on nitro varnish.

The following are not allowed to be installed on the engine:

  • - cotter pins, cotter wire and locking plates, used;
  • - spring washers that have lost elasticity;
  • - damaged gaskets;
  • - parts with more than two clogged or broken threads on the thread;
  • - bolts and studs with elongated threads; bolts and nuts with worn edges.

Bolts and nuts must be properly secured (cotter pins, splint wire, spring and special washers and locknuts).

Assemble the engine in the following order:

  • - clean all mating surfaces of the cylinder block from gaskets stuck and torn during disassembly;
  • - fix the cylinder block on the stand, unscrew the oil channel plug from the rear end and blow all the oil channels with compressed air. Wrap the cork in its place;
  • - if there is a need to replace the clutch housing or it is installed on the cylinder block after repair, it is necessary to first remove two dowel pins from the block, then fasten the crankcase to the cylinder block with six bolts.

A crankshaft is installed in the cylinder block on the outer bearings, to the flange of which the indicator rack is attached.

How to assemble the ZMZ-402 engine

By rotating the crankshaft, check the runout of the hole for the centering shoulder of the gearbox, as well as the perpendicularity of the rear end of the clutch housing relative to the axis of the crankshaft, as shown in fig. 1 and fig. 2.

How to assemble the ZMZ-402 engine

The runout of the crankcase and end faces should not exceed 0.08 mm.

If the runout of the hole exceeds the specified value, you should loosen the bolts securing the crankcase to the cylinder block, and with light blows on the crankcase flange, achieve its correct installation;

  • - after tightening the bolts, the holes for the dowel pins in the clutch housing and cylinder block are expanded to the repair size. The diameter of the hole should be such that no blackness remains in the expanded holes.

After that, pins are pressed into the holes, the diameter of which is 0.015-0.051 mm larger than the size of the holes;

  • - the beating of the end of the crankcase is eliminated by scraping. It should be borne in mind that when checking the above described, it is necessary to use unworn crankshaft and liners. With worn parts, the results will be incorrect;
  • - remove the crankshaft;
  • - replace (if necessary) cylinder liners with new ones as follows:
  • - using a puller (Fig. 3) remove the old sleeve from the block;

How to assemble the ZMZ-402 engine

  • - thoroughly clean the seating surfaces and sealing surfaces on the liner and in the cylinder block from scale and corrosion;
  • - insert a new or repaired sleeve with a red copper gasket put on it. The sleeve must enter the cylinder block freely, without effort;
  • - fix the sleeve holdlem from falling out.

Note. When replacing defective or worn liners with new or repaired ones, their position in the cylinder block is not oriented.

In other cases, before removing the liners from the cylinder block, it is necessary to mark them with serial numbers (count from the water pump and gearbox), and also mark their position in the cylinder block in order to ensure their installation in the previous position during assembly.

When using - worn cylinder liners, as well as each time new piston rings are installed in worn liners, it is necessary to bore on the machine or with a scraper an unworn belt above the upper compression ring.

How to assemble the ZMZ-402 engine

It is necessary to remove the metal flush with the worn part of the sleeve;

- cut off two packings of the crankshaft rear main bearing oil seal (120 mm long each) from the cord, put them in the oil seal block and holder;

Re-assembly the crankshaft:

  • - unscrew all the plugs of the dirt traps of the connecting rod journals and remove deposits from them. Rinse and blow out the oil channels and cavities of the dirt traps with compressed air, screw in and seal the plugs;
  • - check the condition of the working surfaces of the shaft. Nicks, nicks and other external defects are not allowed;
  • - lubricate with refractory grease 1-13 and press the gearbox input shaft bearing into the rear end of the crankshaft;
  • - screw the flywheel to the crankshaft of the engine with a torque wrench (nut tightening torque 7.6-8.3 kgm); cotter pin;
  • screw the clutch pressure plate assembly with the casing to the flywheel, after centering the driven plate with a mandrel (you can use the drive shaft of the gearbox) through the hole in the bearing in the rear end of the crankshaft.

The "O" marks stamped on the casing of the pressure plate and the flywheel near one of the holes for the casing mounting bolts (Fig. 4) must be aligned. Place the clutch disc in such a position that the damper faces the flywheel.

The crankshaft, flywheel and clutch are balanced as an assembly, so dynamic balancing must be done when replacing one of these parts. The imbalance should not exceed 70 Gcm.

When balancing, excess weight is removed from the heavy side by drilling the flywheel metal at a radius of 151 mm with a drill with a diameter of 10 mm to a depth of no more than 12 mm. The distance between the drilling centers must be at least 14 mm.

Node balancing should not be started if the initial imbalance is greater than 180 Gcm. In this case, it is necessary to dismantle the assembly and check the balance of each part separately;

- put on the first main journal of the crankshaft the rear thrust washer with the babbit side to the cheek of the shaft;

How to assemble the ZMZ-402 engine

- crimp the rear shaft seal. To do this, put a mandrel in the hole of the rear main bearing (Fig. 5), install the stuffing box holder and tighten the nuts of the bearing and holder;

wipe the liners of the main bearings in their bed with a clean cloth; put the liners in the bed;

  • - lubricate the main bearing shells and crankshaft journals with clean engine oil and place the crankshaft in the cylinder block;
  • - put the main bearing caps on the cylinder block studs so that the locking tabs on the upper and lower shells of each cover are on the same side, and the numbers stamped on the covers correspond to the bed numbers stamped on the cylinder block near the studs.

When installing the front bearing cap, the tab of the crankshaft thrust bearing rear washer must fit into the groove in the cap. The end of the front bearing cap must be in the same plane as the end of the cylinder block;

  • - put the main bearing caps in place with a light tap with a rubber mallet; the covers must fit into the grooves of the beds of the block;
  • - screw on the nuts for fastening the covers and tighten them evenly, after placing the locking plate. The final tightening must be done with a torque wrench (torque 10-11 kGm), bend the antennae of the locking plate;
  • - install rubber gaskets in the grooves of the stuffing box holder and coat their side surface protruding from the groove with soapy water. Put the stuffing box holder in place and tighten the nuts;
  • - turn the crankshaft, which should rotate freely with little effort.

You can rotate the crankshaft using the flywheel or using a device consisting of a gearbox input shaft with a turnkey square welded to it or a handle with a square hole.

The device can also be used for centering when setting the driven and pressure plates of the clutch;

  • - put the front washer of the thrust bearing with the babbitt side to the shaft so that the pins pressed into the cylinder block and the cover fit into the grooves of the washer;
  • - put the steel thrust washer of the crankshaft with its unworn surface against the babbitted surface of the front thrust bearing washer;
  • - press the crankshaft gear to the stop and check the axial clearance of the crankshaft.

The check is carried out as follows: put a screwdriver (knob, hammer handle, etc.) between the first shaft crank to the front wall of the cylinder block and, using it as a lever, press the shaft to the rear end of the engine.

Using a feeler gauge, determine the clearance between the end face of the thrust bearing rear washer and the shoulder plane of the first main journal. The gap should be within 0.075-0.175 mm;

re-assembly of the connecting rod and piston group:

Clean the piston crowns and piston ring grooves from carbon deposits as shown in fig. 6;

How to assemble the ZMZ-402 engine

  • - in case of replacing a piston, piston pin or connecting rod, you must:
  • - remove the piston pin retaining rings with pliers;
  • - remove the piston pin on the tool (piston rings must be removed before this);

Dimensional groups of pistons and sleeves


Diameter, mm


















- pick up new pistons on liners with a gap of 0.012-0.024 mm. The selection is checked by pulling a probe tape between the piston and the cylinder using a spring steelyard.

The feeler gauge is located in a plane perpendicular to the axis of the piston pin. The piston must be without piston rings.

The pulling force at normal room temperature (+20°C) should be in the range of 3.5-4.5 kg. Tape dimensions: thickness -0.05 mm, width - 13 mm, length - 250 mm;

Dimensional groups for pins, pistons and connecting rods

Diameter, mm



In the piston boss

In the connecting rod bush

Pin and connecting rod




25.0000-24.99 75


















- fit the piston pin to the connecting rod so that at normal room temperature it moves smoothly in the hole of the upper head under a slight effort of the thumb.

Piston pin should be lightly oiled. The color of the pin marking must match the color of the marking on the piston bosses;

How to assemble the ZMZ-402 engine

- make a subassembly of the connecting rod and piston group on the fixture (Fig. 7).

Before pressing the piston pin into it, the piston must be heated in hot water to a temperature of 70 ° C; pressing a finger against a cold piston can damage the surface of the holes in the piston bosses, as well as deformation of the piston itself.

Insert the circlips of the piston pin into the circlipse grooves of the piston bosses;

- select piston rings according to the cylinder; gap; measured at the joint of the ring with a feeler gauge, should be 0.3 - 0.5 mm. In worn cylinders, the smallest clearance should be 0.3 mm;


- use a feeler gauge to check the side clearance between the ring and the wall of the piston groove (Fig. 8). Check the circumference of the piston at several points.

The value of the side clearance should be within 0.050-0.082 mm for the upper compression ring, and 0.035-0.067 mm for the lower compression and oil scraper rings;

  • - put the piston rings on the piston using the tool. Compression rings are placed with an internal chamfer to the piston bottom, as shown in fig. 12, the rings in the grooves should move freely;
  • - wipe the beds of the connecting rods and their caps with a napkin, wipe and insert the liners into them;
  • - turn the crankshaft so that the cranks of the first and fourth cylinders take the position corresponding to the bottom dead center;

How to assemble the ZMZ-402 engine

- lubricate the liners, piston, connecting rod neck of the shaft and the sleeve of the first cylinder with clean engine oil, spread the joints of the piston rings at an angle of 120 ° to each other, put protective brass tips on the connecting rod bolts, compress the rings by crimping or using a cone ring ( Fig. 9), insert the piston into the cylinder.

Before installing the piston, you should once again make sure that the numbers stamped on the connecting rod and its cover correspond to the serial number of the cylinder, check the correct position of the piston and connecting rod in the cylinder; the mark on the piston “Back” should be directed towards the flywheel, and the hole in the lower head of the connecting rod should be in the direction opposite to the camshaft;

- tighten the connecting rod by the lower head to the connecting rod neck, remove the brass tips from the bolts, put on the connecting rod cover so that the numbers stamped on the cover and the connecting rod face the same direction.

Tighten the nuts with a torque wrench (torque 6.8-4.5 kGm) and lock with a lock nut stamped from sheet steel. Lock nut tightening torque 0.3-0.5 kgm;

- in the same order, insert the piston of the fourth cylinder, then turn the crankshaft 180 ° and insert the pistons of the second and third cylinders.

Turn the crankshaft several times, which should rotate easily with little effort;

re-assembly the camshaft:

  • - put on the front end of the camshaft a spacer sleeve and a thrust flange;
  • - press the timing gear onto the shaft and secure it with a bolt and washer;
  • - using a feeler gauge inserted between the camshaft thrust flange and the camshaft hub, check the axial clearance of the camshaft, which should be within 0.1-0.2 mm;
  • - clean the pipe for lubricating the timing gears and screw it with a bolt and a clamp to the block;
  • - insert the assembled distribution room into the hole of the block, having previously lubricated its support journals with engine oil.

When the gears are engaged, the tooth of the crankshaft gear with the “O” mark must be against the notch at the troughs of the teeth of the camshaft gear (see Fig. 17). The side clearance in engagement should be in the range of 0.03-0.08 mm. With a larger or smaller gap, choose another pair;

  • - through the holes in the camshaft gear, attach the thrust flange to the block with two bolts with spring washers;
  • - put the oil deflector on the neck of the front end of the crankshaft with the convex side to the gear;
  • - check the suitability for further operation of the oil seal pressed into the cover of the timing gears. If the oil seal has worn lips or loosely grips the crankshaft pulley hub inserted into the oil seal, replace it with a new one.

It is recommended to press the stuffing box into the cover using a mandrel on a press, as shown in fig. 10;

How to assemble the ZMZ-402 engine

- put on the studs the gasket and the cover of the timing gears;

How to assemble the ZMZ-402 engine

Center the cover on the front end of the crankshaft using a mandrel (Fig. 11) and tighten all the nuts and bolts of the cover.

If there is no centering mandrel, then the cover can be installed on the hubse crankshaft pulley.

The hub must be pressed onto the crankshaft so that its end enters to a depth of 5 mm into the hole in the cover.

After that, fix the cover with nuts, maintaining the same clearance around the circumference between the hub and the opening of the cover.

Align the gap with light blows of a wooden or rubber hammer on the cover. After that, finally fix the cover;

remove the centering mandrel and press on the crankshaft pulley hub;

  • - wrap a ratchet into the crankshaft, after putting a spring washer on it.

Turning the crankshaft by the ratchet, check if the deflector touches the timing gear cover due to deflector bending or a loose fit on the hub;

  • - screw the crankshaft pulley to the hub;
  • - install the oil pump assembly with the oil receiver;
  • - install the breaker-distributor drive;
  • - turn the crankshaft to align the mark c. m.t. on the rim of the crankshaft pulley with a pointer on the timing gear cover (see Fig. 14).

The camshaft cams, which actuate the valves of the first cylinder, must be directed with their tops in the opposite direction from the pushers (towards the oil pan) and are located symmetrically, as shown in fig. 12;

How to assemble the ZMZ-402 engine

- check the axial clearance of the drive shaft using a feeler gauge inserted between the drive housing and the gear. The gap should be within 0.15-0.40 mm;

put a gasket on the studs of the breaker-distributor drive;

How to assemble the ZMZ-402 engine

  • - turn the drive roller to the position shown in fig. 13, a, and put the drive in the socket of the cylinder block.

When inserting the drive into the socket, it is necessary to turn the oil pump shaft so that the end of the drive shaft enters the hole in the pump shaft

In a properly installed drive, the slot in the shaft sleeve should be parallel to the motor axis and offset from the motor, as shown in fig. 13, b;

  • - fix the drive;
  • - check for clearance in the helical gears of the camshaft and the breaker-distributor drive.

If for some reason only one breaker-distributor drive has been removed from the engine, it can be installed without removing the oil pan.

In this case, setting the piston of the first cylinder to c. m.t. compression stroke, when installing the drive, slightly turn the crankshaft in one direction or another.

When the drive is correctly installed, when the piston of the first cylinder is at TDC. compression stroke, the rotor of the breaker-distributor will take a position against the first contact, marked with the number 1 on the cover of the breaker-distributor;

- put the gasket of the oil pan on the flange of the cylinder block;

How to assemble the ZMZ-402 engine

  • - install the assembled pallet on the studs, press it against the block with the help of the fixture (Fig. 14) and fasten it with nuts and washers;
  • - install and bolt the lower part of the clutch housing;
  • - clean the combustion chambers of the cylinder head from carbon deposits, wipe and blow with compressed air. If necessary, clean the holes in the water distribution pipe to remove it, as shown in fig. 15;

How to assemble the ZMZ-402 engine

  • - grind the valves, for this you need:
  • - apply a thin layer of a mixture consisting of one part of M-20 micropowder (GOST 3647-59) and two parts of industrial oil 20 (spindle 3) (GOST 1707-51) to the lapped surface of the valve seat. Stir the mixture thoroughly before use;

put a technological spring on the valve stem, insert the valve into the guide sleeve.

The inner diameter of the spring should be about 10 mm. The spring force is small; it should slightly lift the valve off the seat. When lightly pressed, the valve should sit on the seat;

  • - press the rubber suction cup to the upper plane of the valve head. Suction cup and valve surfaces must be dry and perfectly clean;
  • - rotating the suction cup handle alternately in one direction or the other and at the same time moving the valve up and down, achieve equal numbered matt chamfer on the entire circumference.

Before starting lapping, check for warping of the valve head and burning of the valve and seat.

If these defects are present, it is impossible to restore the tightness of the valve with one lapping, and the seat must first be ground, and the damaged valve replaced with a new one.

If the gap between the valve and the sleeve exceeds 0.25 mm, then the tightness cannot be restored either. In this case, the valve and the sleeve should be replaced with new ones.

How to assemble the ZMZ-402 engine

Valves (for spare parts) are produced in a standard size, and guide bushings - with an inner diameter reduced by 0.3 mm (to deploy them to the final size after being pressed into the cylinder head).

The worn guide bush is pressed out using a punch (Fig. 16). Valve seats are removed by milling with a carbide countersink.

Repair seats have an outer diameter 0.25mm larger than standard, so the seat sockets are bored to:

- for the inlet valve seat - 47.25+0.027mm and for the exhaust valve - 38.75+0.027mm.

The valve seats and guide bushings must be cooled in carbon dioxide (dry ice) before assembly, and the cylinder head must be heated to a temperature of 160-175 ° C.

When assembling, the seats and sleeve must be inserted into the sockets of the cylinder head freely or with light force.

After installing the seat, the metal of the cylinder head is rolled around the seat using a flat mandrel with a diameter of 49 or 41 mm, respectively, centered on the hole in the seat.

How to assemble the ZMZ-402 engine

The new bushing is pressed in from the side of the rocker arms using a punch. The sleeve after pressing should protrude 22 mm above the plane of the cylinder head.

After pressing, expand the sleeve hole to a diameter of 9 + 0.022 mm, and grind the chamfers of the seats, centering on the hole in the sleeve.

To grind the seats, you can use the tool shown in fig. 17. The expanding mandrel is installed in the machined hole in the sleeve, and the mandrel shank serves as the axis for the grinding wheel with a chamfer at an angle of 45 °. The grinding wheel is driven by a small electric motor.

When grinding, ensure that the chamfer on the valve seat is concentric with the hole in the sleeve within 0.03 mm of the total indicator reading.

Chamfers are ground at an angle of 45°. The outer diameter "d" (fig. 16) of the chamfer at the seat for the inlet valve should be 46 mm, and at the outlet - 35 mm.

The width of the chamfer "c" should be 1.8-2.3 mm at the intake valve seat, and 2.3-2.5 mm at the exhaust valve. The chamfer width is obtained by grinding the seat hole at an angle of 30°, as shown in fig. 18, a.

When grinding worn seats, the outer diameter of the chamfer will be larger than the above dimensions. In this case, the outer diameter of the chamfer is adjusted to the required value by grinding the end of the seat at an angle of 30°, as shown in Fig. 18, b.

How to assemble the ZMZ-402 engine

After grinding the seats and lapping the valves, thoroughly clean all gas channels and blow with compressed air so that no abrasive dust remains.

The valve stems are lubricated before assembly with a mixture consisting of seven parts of an oil colloidal graphite preparation (GOST 5262-50) and three parts of MS-20 aviation oil;

  • - insert the valves into the bushings according to the marks made and assemble them with the springs. Make sure that the protrusions of the crackers fit into the annular groove of the valve stem;
  • - put a gasket on the cylinder head studs, install the head and secure it with nuts and washers. Tighten the nuts with a torque wrench with a torque of 7.3-7.8 kGm, following the order indicated in fig. 20;

Cylinder head tightening order

- clean with wire and blow out with compressed air the holes in the rocker arms, in the axle of the rocker arms and adjusting screws, the hole in the rear pillar of the axle of the rocker arms and in the cylinder head.

Check the tight fit of the bushings of the rocker arms.

In the event of a loose fit during operation, the bushing may move and block the valve lifter rod lubrication hole. Such bushings must be replaced;

- sub-assembly of the rocker axis. Before installing each rocker arm, lubricate its bushing with engine oil.

Koromas The legs and uprights are assembled on the axle in such a position that the offset of the holes for the mounting studs in the uprights faces the adjusting screws of the rocker arms. The fourth (rear) rack must have a hole on the bottom plane for the passage of oil;

Pusher Dimension Groups


diameter, mm


Diameter, mm



Gap, mm













  • - insert the pushers into the slots according to the labels on them. Lubricate the tappets and holes in the block with engine oil;
  • - insert the rod assembly with tips into the holes in the cylinder head;
  • - install the assembled rocker axle on the studs and secure with nuts and washers. Adjusting screws with their spherical part should lie on the sphere of the upper tip of the rod;
  • - set the gaps between the end of the rod of the middle valves and the toe of the rocker arm 0.35-0.40 mm, and the extreme valves (exhaust first and fourth cylinders) - 0.30-0.35 mm. This must be done, as indicated in the article "Adjusting valve clearances";
  • - put the gasket and rocker cover and fix them with screws and washers;
  • - lubricate and put on the front cover of the gearbox the clutch release assembly with the bearing and fix the release spring;
  • - put and fix the gearbox;
  • - put the clutch release fork;
  • - put engine parts and assemblies in reverse order.


Repair of the crankshaft consists of regrinding the main and connecting rod journals to the next repair size

The hydraulic clutch release (Fig. 1) of vehicles of the UAZ-31512 family consists of a suspended pedal 19, a master cylinder 5, a hydraulic pipe 4, a hydraulic hose 24 and a working cylinder 25