MAZ car compressor repair

Compressor capacity at 2000 rpm engine crankshaft - 201 l/min

The compressor must be disassembled if there are noises and knocks during operation, as well as if the compressor significantly ejects oil into the discharge pipeline

To remove the compressor from the engine, remove the drive belt, disconnect the pipelines and unscrew the compressor mounting bolts.

Disassemble the compressor in the following order:

• - unscrew the plugs of the discharge valves, remove the springs and valves. Using a 10 x 10 mm square wrench, unscrew the valve seats;
• - remove the compressor pulley with a puller. Knock out the key;
• - unscrew the nuts of the compressor head mounting studs and carefully, after separating the head gasket, remove the compressor head;
• - remove the springs and intake valves from the socket in the cylinder block;
• - unscrew the bolts and remove the air supply pipe;
• - remove the connecting rod caps and remove the pistons with the connecting rods and the assembly from the block;
• - remove the piston rings, remove the plugs and piston pin and separate the connecting rod and piston;
• - unscrew the bolts and remove the front and rear crankcase covers;

• - remove the rear cover seal with a spring, unscrew the thrust nut of the crankshaft rear bearing (Fig. 2) and remove the lock washer;

• - Drive the crankshaft assembly with the front bearing through the front bearing housing in the block. Press the front bearing off the crankshaft (Fig. 3);
• - remove the rear bearing circlip and press the rear bearing out of the block;
• - remove the oil seal from the socket of the front cover;
• - separate the block and the crankcase, unscrew the stud nuts, carefully separating the gasket.

Rinse the parts of the disassembled compressor and carefully inspect. Blow out all channels with compressed air.

Checking the technical condition of compressor parts

During operation, the following compressor defects may appear:

• - in the head of the block - cracks and chips, thread stripping in conical holes for fittings and elbows of pipelines, warping of the plane of contact with the block;
• - in the cylinder block - cracks, breaks or scuffs and wear of the cylinder mirror;
• - in the compressor crankcase - wear of bearing seats, thread failure for bolts and studs of covers and block, chips and cracks;
• - in the crankshaft - wear of the connecting rod journals, the rear cover seal and the front cover oil seal;
• — wear of discharge and inlet valves and their seats, parts of the unloader, shrinkage or breakage of valve springs;
• - in the compressor pistons - scuffing, wear of the skirt, holes for the fingers and breakage of the piston rings;
• - in the compressor connecting rod - wear of the bushing of the upper head and wear of the liners of the lower head.

Strip or wear of the thread in the head of the block and in other parts of the compressor is eliminated by installing screws with subsequent processing to the nominal size.

Worn seats and valves are replaced. After installing a new seat or valve, lapping is required.

Studs and nuts that have stripped threads or do not provide connections must be replaced.

The cylinder block and other parts of the compressor that have chips and cracks should be replaced with new ones.

Cylinders are repaired by boring them, followed by honing to the repair dimensions given in Table 1.

When boring cylinders, the ovality and taper should not exceed 0.03 mm, and the perpendicularity of the cylinder surface relative to the plane of the connector with the crankcase should not exceed 0.03 mm over a length of 100 mm.

Worn pistons and piston rings must be replaced with repair kits indicated in Table. 2.

The difference in the mass of the pistons should not exceed 15 g. When worn to a diameter of less than 34.99 mm, the main journals of the crankshaft are deposited and machined to a diameter of 35 mm.

Worn crankpins are ground to the repair size and sets of connecting rod bearings corresponding to the repair sizes are selected for them

When replacing the compressor piston group, pistons, connecting rods and pins must be selected in groups (see table).

Group details are color-coded. Piston and piston pin should be selected from the same troupe. When selecting a connecting rod, it is allowed to install a finger of an adjacent group.

Cranks with a bend are subjected to editing. Nepar the allelism of the holes of the connecting rod heads is allowed no more than 0.1 mm over a length of 100 mm.

The front cover oil seal, which does not provide tightness, and worn parts of the rear seal are not repairable and must be replaced.

Compressor assembly

The compressor must be assembled in accordance with the technical requirements in the following order:

• - assemble the piston with the connecting rod. When installing the piston pin into the connecting rod, it must fit snugly into the connecting rod hole under the force of the thumb.

Piston and connecting rod are selected at an ambient temperature of 10 - 30˚ C without the use of lubrication, and during the final assembly of the piston-pin, connecting rod-pin, lubricate with engine oil;

• - install piston rings on the piston (Fig. 4). Install the compression rings with the groove on the inner diameter up.

Set the joints of the compression rings in the vertical plane of the axis of the piston pin from diametrically opposite sides of the piston;

• - press the crankshaft rear ball bearing into the compressor crankcase until it stops against the retaining ring. Press the front bearing onto the crankshaft until it stops.

Install the crankshaft in the crankcase, put on the lock washer of the rear bearing, tighten the nut until the inner race of the bearing stops in the crankshaft and lock it;

• - install the front crankcase cover, having previously pressed the oil seal into it. Lubricate the crankshaft journal with engine oil before installing the cover;
• - install the spring and seal in the crankshaft seat. When installing the spring, insert its ends into the drilling of the crankshaft and seal.

Install the rear crankcase cover. Through the hole in the cover, check the possibility of free movement of the seal in the socket. Turn a cranked shaft; turning force should not exceed 3 Nm;

• - press the seat block 17 (see Fig. 1) and the guides 26 of the inlet valves into the block; install inlet valves 25;
• - lubricate the plungers with engine oil and install them in the seats assemblies with rubber rings. The plungers in the sockets must move freely under a force of 5 N. Install the stems with sockets assemblies, the spring and the unloader rocker;
• - install the gasket and assemble the crankcase with the cylinder block;
• - lubricate the cylinder mirror, crankshaft journals, piston rings and main bearings with engine oil;

• - install the pistons assembled with connecting rods and compression rings into the cylinders using a crimp (Fig. 5) ;

After installing the connecting rod bearings, assemble the lower connecting rod heads. Tightening torque for connecting rod bolts 12.25 - 13.7 Nm.

Align the cotter pin hole in the nut and the connecting rod bolt by tightening the nut. It is not allowed to loosen the nut to install the cotter pin;

• - check the ease of rotation of the crankshaft; the moment for turning the crankshaft should not be more than 3 Nm;
• - install the gasket and cylinder head. Tighten the head stud nuts evenly in two steps with a tightening torque of 12-17 Nm (Fig. 6);

• - screw the seats 18 (see Fig. 1) of the discharge valves into the sockets of the cylinder head, install the discharge valves 21, the springs 19 of the discharge valve and screw the plugs 22 of the discharge valve into the head;
• - install the key and press the drive pulley. Fasten the pulley with a nut and cotter;
• —Test the compressor.

Compressor test

The test is carried out on a special stand at 1200-1350 rpm of the crankshaft and oil pressure in the lubrication system of 118-245 kPa. The oil temperature must be at least 50 °C.

When the compressor is idling for 4-5 minutes, check by touch and ear:

• - bearing heating;
• —bearing noise;
• —knock of pistons (knock should not be);
• - knock of fingers (knock should not be);
• - oil leakage (there should be no leakage).

After testing, install the compressor on the engine and adjust the mutual position of the fan and compressor pulleys, adjust with gaskets.

Adjust the tension of the compressor drive belt.

Since 1999, a compressor with a capacity of 270 l / min at 2000 rpm of the crankshaft has also been installed, which is distinguished by the design of the valve system.

Distinguishing feature of a compressor

• —the absence of pressure valve plugs and the presence of a cover in the cylinder head.

Disassembly, check of technical condition, assembly and testing are similar to the compressor with a capacity of 201 l / min, with the exception of a slightly different order of removal and installation of the head of the valve system.

Table 1

Part name	Rated size, mm	Repair dimensions, mm
		Р1	Р2
Cylinder block	60+0.03	60.40+0.03	60.80+0.01
Compressor piston	59.9-0.03	60.30-0.03	60.70-0.03
Piston rings compression	60.00	60.40	60.80
Piston rings oil scraper	60.00	60.40	60.80
Connecting rod bearings compressor (liner thickness)	1.75-0.013	1.19-0.013	2.05-0.013
Crankshaft (diameter of crankpins)	28.5-0.021	28.2-0.021	27.9-0.021

Table 2

Table 2
Group	Pin diameter, mm	Marking color
I	12,500 – 12,497	Blue
II	12,497 – 12,494	Red
III	12,494 – 12,491	White
IV	12,491 – 12,488	Green