The cylinder head is a one-piece gray cast iron and is attached to the block with studs screwed into the block

The studs are made of chromium-nickel steel and heat-treated

To ensure heat dissipation, the cylinder head has a water jacket that communicates with the block jacket; to ensure fuel supply to the nozzle, there are holes for fittings in the side surface.

The cylinder head contains valves with springs and parts for their fastening, rocker arms, rocker axles and nozzles.

The valve seats are plug-in.

The inlet valve seats are made of special cast iron, and the exhaust valve seats are made of a special heat-resistant alloy.

The seats are pressed into the seats with an interference fit.

Seats and sintered valve guides are finished after being pressed into the head.

Scheme for installing seals in a metal gasket (MAZ diesel)

The cylinder heads installed on the engines have structural differences:

Cylinder heads on YaMZ-236NE2,BE2 engines can be block for three cylinders each or individual:

  • - Block head for three cylinders each. The mating surface is ground and annular grooves are made in the sealing area of ​​the cylinder liners.

The junction of the cylinder head, block and liner is sealed with a gasket consisting of a metal gasket, common for three cylinders, sealing the gas joint, and rubber sealing elements sealing the oil, water and rod cavities.

Sealing elements of five types in the amount of 14 pcs. on the gasket (fig. 1).

Sealing the joint between the sleeve and the MAZ block

An individual head is installed on each cylinder and is attached to the block with six studs, having a length of 209 mm and 248 mm.

A cast-iron nozzle cup is pressed into the head.

The top of the glass is sealed with a rubber ring.

The mating surface in the area of ​​sealing cylinder liners has three annular grooves.

The junction of the cylinder head, block and liner (Fig. 2) is sealed with a gasket consisting of a metal gasket sealing the gas joint and a rubber gasket sealing the oil, water and rod cavities.

A metal and rubber gasket is installed on the pins of the block.

The metal gasket is available in four thicknesses (1.1 mm; 1.3 mm; 1.5 mm; 1.7 mm) and is selected individually during engine assembly in order to achieve the optimal working process in each cylinder.

A 1.7 mm thick gasket is supplied as a spare part.

Cylinder heads on YaMZ-236N engines; (B; NOT; BE) block for three cylinders each. Structurally, it is basically the same as the previous block one.

Remove the cylinder head only for troubleshooting parts of the cylinder-piston group, cylinder head gasket, valves, or to replace the head itself.

Remove the cylinder head in the following order:

  • 1. Drain the coolant from the engine cooling system.
  • 2. Disconnect all pipelines from the head, protect their internal cavities from dust and dirt.
  • 3. Remove the cylinder head cover.

Unscrewing the MAZ injector bracket fixing nutMAZ cylinder head repair

  • 4. Unscrew the nuts of the nozzle fastening brackets (Fig. 3), remove the nozzles (Fig. 4), protecting the atomizer from impacts and clogging of holes
  • 5. Unscrew the nuts securing the rocker axles, remove the rocker axles complete with the rocker arms and remove the rods.

Unscrewing the MAZ cylinder head nuts

6. Loosen the cylinder head nuts (Fig. 5) in reverse order to tightening (Fig. 6).

MAZ intake valve seat processing

Remove the individual cylinder head nuts in at least three steps:

  • 1 - reception - up to 147...118 Nm (15...12 kgcm)
  • 2 - reception - up to 49...39 Nm (5...4kgcm)
  • 3 - trick - unscrew the nuts.
  • 7. Remove the cylinder head from the engine and inspect its condition.
  • 8. If necessary, carefully remove the cylinder head gasket.
  • 9. Check the condition of the cylinder liners and close the cylinder bores to protect them from dust and dirt.

Install the cylinder head on the engine in reverse order.

Before installing, wipe the mating surfaces of the cylinder block, cylinder liner collar and cylinder head with a clean rag.

Reuse of the cylinder head gasket is allowed with the same cylinder head only with the same position of the liners in the cylinder block and in the absence of traces of gas breakthrough and destruction of the gas joint edging.

Pay attention to the correct installation of the cylinder head gasket on the pins and the gasket edges on the cylinder sleeve flanges.

MAZ cylinder head tightening sequence

Tighten the cylinder head nuts in ascending order of numbers, as shown in fig. 7, torque 240 - 260 Nm (24 - 26 kgcm).

After the first tightening, by a second operation, check the required torque on each nut, following the sequence indicated.

You must not tighten the nuts with a torque greater than indicated, as this will inevitably lead to the destruction of the parts of the gas joint.

Layout of seal parts at the MAZ gas joint

The junction of the cylinder head, block and liner (Fig. 8) is sealed with a gasket made of a sandwich material with edging of cylinder holes and holes for the passage of coolant.

Split sealing PTFE rings are inserted into the edges of the cylinder holes.

The block is fastened with 16 studs with washers and nuts.


Before disassembling the cylinder heads, clean them of oil and carbon deposits and mark the serial numbers of the valves on their plates in order to install them in their places during assembly.

MAZ valve timing tool

To dry out the valves, it is necessary to install the cylinder head without injectors, rocker arms, rocker arm axles and rocker arm axle mounting studs with the mating surface on the plate so as to provide a stop for the valves.

Drying out is carried out using the device shown in fig. 9

For this purpose, screw the stop bolt 1 of the device into the hole for the stud for attaching the rocker arm axis, install the pressure plate 2 of the device on the spring plate of the corresponding valve and, pressing the handle 3 of the device lever, press the valve springs, remove the crackers and remove all parts of the valve assembly .

In the same way, sequentially dry out all the other valves and remove the valve springs and associated parts.

Turn the cylinder head and remove the valves from the guides.

Valves and seats should be thoroughly cleaned of dirt, carbon and oil deposits, washed in kerosene or a special cleaning solution, dried and inspected to determine the degree of repair.

It is possible to restore the tightness of the valve by lapping only if there is slight wear and small shells on the working chamfer, and only if; if the poppet and stem are not warped and there are no local burnouts on the chamfers of the valve and seat.

In the presence of such defects, lapping should be preceded by grinding seats and valves or replacing defective parts.

To lap the valves, use a special lapping paste prepared by thoroughly mixing three parts (by volume) of green silicon carbide micropowder with two parts of engine oil and one part of diesel fuel.

Stir the lapping mixture thoroughly before use, since in the absence of mechanical stirring, the micropowder can precipitate.

Mount the cylinder head on a plate or special tool with the mating surface up.

Apply a thin, even layer of lapping paste to the valve face, lubricate the valve stem with clean engine oil and install it in the cylinder head.

Lapping is performed by reciprocating rotational movements of the valves using a special tool or a drill with suction.

Pressing the valve with a force of 20-30 N (2-3 kgf), turn it ⅓ of a turn in one direction, then, loosening the force, ¼ turn in the opposite direction. Do not lap in a circular motion.

Lapping the gas distribution valves (matte belt arrangement)

Periodically lifting the valve and adding paste to the chamfer, continue lapping, as indicated above, until a continuous matte belt with a width “A” of at least 1.5 mm appears on the chamfers of the valve and seat (Fig. 10).

Ruptures of the matte belt and the presence of transverse marks on it are not allowed.

When properly lapped, the matte "A" band on the valve face and seat should start at the larger base of the cone, as shown in Figure 10.

After lapping, thoroughly wash the valves and cylinder head with kerosene or a special cleaning solution and dry.

Install the valves, springs and their mounting parts on the cylinder head and dry the valves using the tool shown in fig. 9.

Check the quality of grinding for leaks at the valve-seat interfaces by pouring kerosene or diesel fuel, pouring it alternately into the inlet and outlet windows. Well lapped valves should not let kerosene or diesel fuel through for one minute.

It is acceptable to check the quality of lapping with a pencil; for this, apply 10-15 lines at regular intervals with a soft graphite pencil across the chamfer of the lapped clean valve, then carefully insert the valve into the seat and, pressing hard against the seat, turn it ¼ turn.</ p>

If the lapping quality is good, all the dashes on the working chamfer of the valve should be erased. If the results of the lapping quality check are unsatisfactory, it must be continued.

The main defects of the cylinder head are:

  • - cracks, workings, risks and shells on the saddles of the exhaust and intake valves, violation of the nozzle cup seal;
  • - wear of the holes in the valve guide bushings, weakening of the fit of the guide bushings in the cylinder head;
  • - cracks on the surface of the head to the cylinder block and warpage of this surface, as well as bending and loosening of the fit of the studs on the cylinder head or damage to the threads on the studs.

The cylinder head is replaced if there are cracks passing through the holes for the valve guides, holes for the injector cups and valve seats, and cracks on the walls of the cooling jacket in places inaccessible for repair.

The presence of cracks is established by external inspection, as well as when testing cylinder heads for tightness with water under a pressure of 0.4 MPa (4 kgf / cm2).

The tightness of the cylinder head cooling jacket can be checked by introducing compressed air into it and immersing the head in a bath of water.

Cracks will be visible from the emerging air bubbles.

Cracks and holes in the cylinder head are not allowed, only small cracks are allowed on the mating plane between the holes for the sprayer of the nozzle and valves, which do not capture the working chamfer of the intake valve and do not violate the tightness.

MAZ car valve grinding

If during the test of the cylinder head for leaks, a violation of the seal of the injector cup is detected, tighten the cup fastening nut. If the leak is not eliminated, the glass is removed and the sealing ring and washer are replaced, and, if necessary, the glass.

To install the glass, put washer 4 on the bottom of the socket under the nozzle glass (Fig. 11),

install a sealing rubber ring 6 in the socket, having previously lubricated it with solid oil, insert the glass 5 of the nozzle with a certificate until it stops and screw the nut 7 of the nozzle cup with the head (Fig. 12), tightening the nut with a torque of 90-110 Nm (9-11 kgf. m).

Then repeat the leak test of the nozzle cup seal.

Head for turning the nut of the MAZ injector cup

The block heads are allowed to be assembled without repair if:

  • - non-flatness of the surface adjacent to the block, not more than 0.1 mm over the entire length and not more than 0.05 over a length of 100 mm;
  • - if the width of the working chamfer of the inlet valve seat is 2.0-2.8 mm, the exhaust valve is 1.5-2.3 mm;
  • - sinking of the intake valve relative to the lower plane of the cylinder head - no more than 2.2 mm, and the exhaust valve - no more than 2.7 mm;
  • - if the diameter of the inner surfaces of the valve guides is no more than 12.060 mm and if there are no more than two broken threads in the thread for the studs.

The non-flatness of the surface adjacent to the block is corrected by grinding, providing the required non-flatness and head height to the annular rib of at least 131.5 mm; nominal size - 132-0.26 mm.

When the threads are worn or broken in the holes of the cylinder head, a repair size thread is cut or screws are installed.

The cylinder head is threaded for repairnye studs of the following sizes: water distribution pipe - M10 x 1.5T to a depth of 14 mm; inlet and outlet pipelines - M12 x 1.75T to a depth of 15 mm; nozzle brackets - M14x2T to a depth of 22 mm.

When repairing threaded holes by setting screw drivers, a hole with a defective thread is drilled and a thread is cut for the screw.

Then, the screwdriver is lubricated with red lead or liquid glass and screwed into the threaded hole until it stops, the end is cut flush with the plane of the head, the screw is punched at three points and the threaded hole of the screw is calibrated.

The hole for the nozzle mounting pin cannot be restored.

Drift for pressing the MAZ valve bushing

The valve guide bushings are replaced with new ones when the inner diameter is worn more than 12.06 mm.

Using a mandrel (Fig. 13), the valve guide bushings are pressed into the hole of the cylinder head and treated with a reamer for a nominal 12+0.019 mm or repair 11.6+0.019 mm dimensions .

The valve guides are pressed in with an interference of 0.03-0.05 mm. They should protrude above the valve spring seat by (31±0.5).

Before pressing, the guide bushings are impregnated with oil for three hours, and the head is heated to a temperature of 160-170°C.

When the hole in the cylinder head is worn, a repair guide bush is placed under the guide bushing more than 19.03 mm, for this, the hole is reamed to a diameter of 19.2+0.023 mm and the repair bushing is pressed in.

Valve seats are restored depending on the nature of the defect. The working chamfers of the valve seats are processed only after the restoration of the holes in the valve guide bushings.

Risks on the working surface of the seat of the inlet and exhaust valves, wear and dents are eliminated by countersinking or grinding the chamfer of the seat, while ensuring the minimum necessary metal removal until a clean surface of the seat chamfer is obtained.

The maximum sinking of the new valve disc from the head plane with restored chamfers of the head seat is allowed: 2.5 mm for the intake valve and 3.0 mm for the exhaust valve.

The bevel repair cutting tool must be oriented to the inside diameter of the valve guide to ensure that the bevel and the inside diameter of the valve guide are aligned within 0.025mm (0.05mm runout).

Intake valve seat machining

Chamfer the intake valve seat in the following order:

  • - mill the working chamfer with a countersink at an angle of 120° (Fig. 14, a) until a clean, even surface is obtained;
  • - mill the lower edge of the working chamfer with a countersink at an angle of 150° (Fig. 14, b), maintaining the required chamfer width within the diameter of 59.4+0.7mm;
  • - mill the upper edge of the chamfer with a countersink at an angle of 60° (Fig. 14, c) until the width of the chamfer is 2.0-2.5 mm.

Chamfer the intake valve seat in the following order:

  • - mill the working chamfer with a countersink with an angle of 90° (Fig. 15, a) until the required cleanliness is obtained;
  • - by milling the lower edge of the chamfer with a countersink with an angle of 150 ° (Fig. 15, b), ensure the size of the working chamfer in the range of 1.5–2.0 mm.

Exhaust valve seat processing

Risks and slight wear on the valve seats are eliminated by grinding the seats, followed by lapping of the valves.

If it is impossible to obtain the width of the working chamfer on the exhaust valve seat equal to 1.55 - 2.0 mm and the inlet valve equal to 2.0-2.5 mm, as well as in the presence of burnout, cracks, pits and other defects, not eliminated by processing, the saddles are replaced.

The repair seat of the intake valve is made of cast iron, the chemical composition of which is similar to that of the cylinder head cast iron, and the exhaust valve is made of special cast iron. Casting hardness HRC 50—60.

MAZ inlet valve repair seat

The socket for the repair seat in the cylinder head is bored on a radial drilling machine. The processing of the head for the repair seat of the intake valve, the dimensions of the seat and the processing of the chamfer of the seat assembly with the head are shown in fig. 16.

After boring, the runout of the surface "D" relative to the hole for the valve sleeve should be no more than 0.1 mm, the non-perpendicularity of the end face "T" of the surface "D" should not exceed 0.03 mm at the extreme points.

When pressing in a new seat, the cylinder head is heated in boiling water to 90 ° C and kept at this temperature at least 3 minutes.

The seat is pressed in with light blows of a hammer through a copper or brass spacer, ensuring an interference of at least 0.02 mm.

The fit of the seat to the cylinder head is checked with a feeler gauge. A probe with a thickness of 0.05 mm should not pass through.

After pressing in, the valve seats are processed according to the technology described above, which provides the necessary geometric dimensions of the working chamfer of the valves.

Engine head valves are made of various materials.

MAZ exhaust valve dimensions

The end of the exhaust valve stem (Fig. 17) is made of 40KhN steel, and the head with the stem is made of 4Kh14N14V2M steel. The valve is hardened and tempered to the head hardness HRC25-30 and the end of the rod HRC 50-57.

The inlet valve is made of 4X10CM2 steel and heat-treated to a hardness of HRC 35-40, and the end face to a hardness of HRC 50-57, to a depth of 2-3 mm.

The main defects of valves are wear or burnout of the working chamfer, bending or wear of the stem along the diameter, as well as wear of the end face of the valve stem.

To eliminate wear or burnout of the working chamfer, it is ground cleanly to a roughness of 0.63 microns. In this case, the height of the cylindrical part of the head must be at least 0.5 mm, and if the height is less than 0.5 mm, the valve is rejected.

The chamfer of the exhaust valve is ground at an angle of 45°, and the inlet valve at an angle of 60°.

Tightening order for MAZ cylinder head nuts

The ground working chamfer of the exhaust valve must have the following parameters:

  • - the thickness of the belt of the cylindrical surface of the plate is not less than 1.0 mm, the angle is 91-92°, the surface roughness is 0.63 microns;
  • - the beating of the working surface of the chamfer relative to the rod is not more than 0.03 mm, and, accordingly, the inlet: the thickness of the belt of the cylindrical surface of the plate is not less than 0.75 mm, the angle is 121-122 °, the surface roughness is not lower than 1.25 microns;</ li>
  • - runout of the working chamfer relative to the rod is not more than 0.03 mm.

Usually, before grinding the valve, its stem is checked for bending and corrected if necessary.

To check for bending, the valve stem is placed on indicator prisms and the non-straightness of the generatrix of the valve stem is checked, which should be no more than 0.01 mm, and the runout of the working chamfer relative to the generatrix should be no more than 0.03 mm.

Editing is done with light blows of a wooden or lead hammer.

When the valve stems are worn, they are ground to a repair size to diameters: for inlet - 11.8-0.030 mm or 11.6-0.030 and outlet - 11.8 -0.095 mm or 11.6-0.070 mm.

When grinding on a centerless slotted machine using the plunge method, it is necessary to subsequently deepen the annular groove under the crackers to a diameter of 10.1-0.12 mm.

When grinding on a cylindrical grinding machine, the valve end is inserted into a mandrel with a cylindrical hole and pressed by the center from the side of the valve head.

The mandrel with a tapered surface is mounted in the machine spindle. After grinding, the rod is polished to a roughness of 0.16 microns.

Ovality and taper of the generatrix of the rod surface is allowed no more than 0.01 mm.

Worn valve stems are restored by remaining, followed by grinding to a nominal diameter: Exhaust valve - 12-0.070 mm and inlet valve -12-0.030.

Valve stems with wear in diameter less than 11.45 mm are rejected.

The worn end of the valve stem is ground and polished to a roughness of 0.32 microns, followed by chamfering 0.45 x 45°

If the distance from the annular groove to the end of the valve stem is less than 7.2 mm, the end is welded with a T-590 electrode or U8 high-carbon wire.

Then the end face is ground, hardened to a hardness of HRC 50-57 and polished. At the same time, it is necessary to maintain a size of 7.4 -0.1 mm and ensure the perpendicularity of the end face relative to the generatrix of the valve stem; a deviation of no more than 0.1 mm is allowed over a length of 100 mm (see Fig. 17).

The valve springs are made of 50HFA steel. Springs usually have the following defects: loss of elasticity, coil breaks and cracks.

If there are broken coils or cracks, the springs are rejected.

Before being installed on the engine, the springs are tested for elasticity on a hydraulic device, which makes it possible to determine the length of the spring depending on the load.

The outer spring is considered suitable for installation if the free length is at least 74 mm, and at a load of 23.5 - 26.5 kgf at least 56 mm.

Internal spring in a free state 63 mm, should have a length with a load of 12.5 - 13.5 kgf 50 mm long.

The valve rocker (fig. 19) is made of steel 45, and the bushing is made of bronze Br. OCS 4-4-2.5.

Pove The roughness of the toe of the rocker arm is hardened to a depth of 2-5 mm with a hardness of HRC 56 - 63.

MAZ valve rocker

The main defects of the rocker arm are: wear of the hole in the sleeve for the axis of the rocker arm, weakening of the fit of the bushing in the rocker arm and wear of the toe surface.

The rocker is changed when a crack or break is detected.

When the hole for the rocker axle is worn up to a diameter of 25.15 mm, only the bushing is replaced. In addition, the sleeve is replaced when its fit in the rocker is loosened.

The landing is checked with light blows with a copper drift.

Before installing a new bushing, check the bore diameter of the rocker hub, which should be no more than 27.028 mm. The new bushing is pressed into the rocker arm with an interference of at least 0.7 mm.

When installing a new bushing, ensure that the holes in the bushing and the rocker arm match, and the joint of the bushing must be at the top of the hole.

The oil groove in the bushing must pass through the aligned hole, and the edges of the groove must not protrude beyond the hole. The pressed new bushing should sink into the body of the rocker by 1 mm on both sides.

The pressed-in bushing is reamed to fit the diameter of 25+0.030 mm.

Installing a new design rocker arm on an old MAZ axle

The wear of the rocker toe surface is checked with a feeler gauge using a template with a sphere generatrix radius of 15-0.1 mm. A probe 0.2 mm thick must not pass between the generatrix of the nose and the template.

The indicated defect is eliminated by grinding to a size (see Fig. 19) of at least 19 mm with a radius of 15 mm and a roughness of 0.63 microns, which is obtained by polishing with GOI pastes.

Grind by hand on a rough grinding machine with a grinding wheel, which must be filled with a radius of 15 mm.

If grinding the toe of the rocker does not allow to remove traces of wear without violating the size of 19 mm, then the surface is deposited with a T-590 electrode, which provides a hardness of HRC 50, further processing of the surface of the toe is similar to that described above.

On some engines, rocker arms with a reduced hub width from 34.9-0.14 mm to 30-0.14 mm are installed, the length of the rocker arm sleeve has been changed accordingly from — 0.34-0.34 mm to 29-0.28 mm.

Therefore, when installing a new rocker arm 1 (Fig. 19) on the axle 3 of the old design, it is necessary to install one spacer ring 2 on both sides of the rocker hub, made of any steel according to the dimensions shown in the figure.

When installing an old rocker arm on a new design axle, it is necessary to cut its hub evenly on each side by 2.5 mm; the ends of the rocker hub must be perpendicular to the axis of the inner diameter of the bushing with an accuracy of 0.1 mm on a diameter of 30 mm.

The new bushing can be pressed in and processed as an assembly with the old rocker arm, if the specified requirements are met when using the old bushing with the new rocker arm, it should be pressed in and cut on both sides.