The gas distribution mechanism serves to ensure the intake of fresh air charge into the cylinders and the exhaust gases from them
The intake and exhaust valves open and close in certain positions of the piston, which is ensured by the combination of marks on the gears of the drive units during their installation.
The timing mechanism is an upper valve with a lower camshaft arrangement.
Camshaft cams 24, in accordance with the timing phases, actuate the pushrods 23.
The rods 19 report the rocking motion of the rocker arm 16, and they, overcoming the resistance of the springs 4 and 5, open the valves 25.
The valves are closed under the action of the compression force of the springs.
The camshaft is steel, the cams and support necks are subjected to heat treatment of HDPE;
- it is installed in the collapse of the cylinder block on five sliding bearings, which are steel bushings filled with antifriction alloy.
The diameter of the bushings is 6 mm larger compared to the bushings of the engine mod. 740.10.
Camshaft of increased dimension, changed valve timing phases and valve stroke compared to the camshaft of the engine mod. 740.10.
A straight-toothed gear 3 is pressed onto the rear end of the camshaft.
The camshaft is driven from the crankshaft gear through intermediate gears.
Gears are steel, stamped with heat-treated teeth.
To ensure the specified timing phases, the gears during assembly are installed according to the marks stamped on the ends
From the axial movement, the shaft is fixed by the housing 2 of the rear support bearing, which is attached to the cylinder block with three bolts.
The landing diameter of the rear support bearing housing is larger compared to the motor bearing housing mod. 740.10.
Installation of the bearing housing of the rear support of the camshaft of the engine mod. 740.10 is not allowed, as it will lead to an emergency decrease in oil pressure in the system and premature failure of the engine.
Valves made of heat-resistant steel.
The angle of the working chamfer of the valves is 90°. The diameter of the intake valve plate is 51.6 mm, the exhaust valve is 46.6 mm, the lifting height of the intake valve is 14.2 mm, the exhaust valve is 13.7 mm.
The geometry of the plates of the intake and exhaust valves provide the appropriate gas dynamic parameters of the intake and exhaust gases and therefore their replacement with the valves of the engine mod. 740.10 is not recommended.
The valves move in guide bushings made of cermet.
To prevent oil from entering the cylinder and reduce its consumption for carbon monoxide, rubber sealing cuffs are installed on the valve guides.
The pushers of the poppet type with a profiled guide part are made of steel with subsequent surfacing of the plate surface with bleached cast iron.
The pusher is subjected to chemical and thermal treatment.
The rocker arms of the valves are steel, stamped, represent a double-shouldered lever, in which the ratio of the large shoulder to the smaller is 1.55.
The rocker arms of the intake and exhaust valves are mounted on a common rack and fixed axially by a spring lock.
Rocker arms of engine valves 740.11-240. unlike the rocker arms of the mod. 740.10 engine, they do not have a bronze sleeve.
The pusher guides are cast together with the cylinder block.
Push rods are steel, hollow with pressed tips. The rods are 3 mm shorter than the rods of the engine mod. 740.10 and are not interchangeable with them.
The rocker arm is cast iron, its trunnions are subjected to heat treatment of HDPE.
The diameter of the trunnions is 2 mm larger compared to the trunnions of the rocker arm strut of the mod. 740.10 engine.
The valve springs are screw-mounted, two are installed on each valve.
The springs have different winding directions.
The wire diameter of the outer spring is 4.8 mm, the inner one is 3.5 mm. The pre-installed spring force is 355 N, the total working force is 821 N.
The springs are interchangeable with the springs of the engine mod. 740.10.
Cylinder heads 1 (Fig. 1) are separate for each cylinder, made of aluminum alloy.
The cylinder head has a cooling cavity communicating with the cooling cavity of the unit.
To strengthen the bottom of the head, its thickness in the exhaust channel area has been increased and an additional rib has been made compared to the cylinder head of the engine mod. 740.10.
Each cylinder head is mounted on two mounting pins pressed into the cylinder block and fastened with four alloy steel bolts.
One of the mounting pins simultaneously serves as a sleeve for supplying oil to lubricate the rocker arms of the valves.
The bushing is sealed with rubber rings.
In the head, in comparison with the engine head 740.10, the opening of the engine oil drain from under the valve cover into the rod cavity is enlarged.
The intake and exhaust duct windows are located on opposite sides of the cylinder head.
The intake duct has a tangential profile to ensure optimal rotational movement of the air charge, which determines the parameters of the working process and environmental performance of the engine, therefore, replacement with the cylinder heads of the engine mod. 740.10 is not allowed.
Cast-iron seats and metal-ceramic valve guide bushings are pressed into the head.
Valve seats have an increased tension in the fit compared to the seats of the engine mod. 740.10, and are fixed with a sharp edge.
The exhaust seat and valve are profiled to provide less resistance to exhaust gases.
The use of the exhaust valve mod. 740.10 is not recommended.
The joint "cylinder head - sleeve" (gas joint) is non-laying (Fig. Gas joint).
A steel sealing ring 3 is pressed into the bored groove on the lower plane of the head. By means of this ring, the cylinder head is mounted on the sleeve collar.
The tightness of the seal is ensured by high precision processing of the mating surfaces of the sealing ring and cylinder liner 5.
The sealing ring additionally has a lead coating to compensate for the micro-dimensions of the sealed surfaces.
To reduce harmful volumes, a fluoroplastic filler gasket 4 is installed in the gas joint.
The filler gasket is fixed on the protruding belt of the gas joint ring due to the reverse cone with tension.
The use of filler gaskets reduces the specific fuel consumption and the smokiness of exhaust gases. The pad is a single-use filler.
To seal the bypass channels of the coolant, sealing rings 2 made of silicone rubber are installed in the holes of the bottom of the head.
The space between the head and the block, the holes of the engine oil drain and the holes of the passage of the rods are sealed with a gasket 7 of the cylinder head made of heat-resistant rubber.
When assembling the engine, the cylinder head mounting bolts should be tightened in three steps in ascending order of numbers indicated in Fig. 5
The values of the tightening torques must be:
1 reception - up to 39-49 Nm (4-5 kgf.m);
2 reception - up to 98-127 Nm (10-13 kgf.m);
3 reception - up to 186-206 Nm (19-21 kgf.m
Before screwing in, lubricate the bolt threads with a layer of graphite grease.
After tightening the bolts, it is necessary to adjust the gaps between the valves and rocker arms
The valve mechanism is closed with an aluminum cover 15 (see Fig. 1).
A vibration isolation washer 14 and a rubber sealing gasket 19 are used for sound insulation and sealing of the cap - cylinder head joint.
Tighten the cylinder head cover bolts with a torque of 12.7-17.6 Nm (1.3-1.8 kgf.m).
The main malfunctions of the gas distribution mechanism
Deviations in the operation of the valve timing mechanism with natural wear of parts cause deterioration of the dynamics of the mechanism, contribute to accelerated wear of the interfaces. Of the total number of failures of all engine systems, 25-27% are due to timing.
The main engine malfunctions caused by timing malfunctions may be the following:
- reducing engine power, increasing fuel and oil consumption;
- increasing the smoke content of exhaust gases;
- reduction of oil pressure in the engine system at temperatures above 0 ° C;
- unstable engine idling;
- engine operation with interruptions or overheating;
- leakage of liquid in the connections of the cooling system.
Signs of timing malfunctions are knocks in the cylinder head. A ringing knock in the cylinder head is caused by the knocking of the valves on the rocker arms due to the large thermal gap between the valve and the toe of the rocker arm.
A dull metallic knock at idle and its amplification during fuel supply are a sign of valve springs failure or valve jamming.
A loose fit of the valve on the seat occurs when there is no or a decrease in the thermal gap between the toe of the rocker arm and the valve, as well as when the bearing capacity of the fixed connection of the cylinder head – valve seat is violated.
If the valve does not fit tightly on the seat, gaps form in certain areas between the valve and the seat.
Incandescent gases under pressure and at high speed pass into the formed cracks, so the chamfer surfaces in this place are intensively corroded, the fit of the chamfer to the saddle worsens.
Combustion products accumulate on the surface of the chamfer, as a result of which the tightness of the connection is violated.
Analysis of the characteristic damage to the valves and their seats shows that approximately 90% of all damage occurs when the tightness of the seat –valve connection is violated.
With an increase in the thermal gap, the lifting height of the valves decreases, as a result of which the filling and cleaning of the cylinders deteriorates, shock loads and wear of timing parts increase.
With very small thermal gaps, as a result of combustion or wear of the working chamfers of the valve or the valve seat, the tightness of the combustion chamber is not ensured, the engine loses compression, overheats and does not develop full power.
The most common timing malfunctions are as follows:
- premature wear of the seat and valve seat surfaces; wear of the valve guide sleeve;
- violation of the stability of the landing in the coupling of the valve seat - cylinder head;
- deformation of the cylinder head;
- deformation of the valve seat and stem;
- deformation of the valve plate; valve stem breakage and corrosion; wear of the tappet holes;
- wear of camshaft bushings; wear of camshaft cams; wear of valve rocker arms.
Before performing technical maintenance, individual monitoring of the timing system condition is necessary, which allows using special equipment, without disassembling the engine, to identify the above-mentioned hidden malfunctions in advance and determine the list of preventive and repair actions.
The technical condition of the timing belt should be assessed by diagnostic parameters, and the need to perform maintenance and repair operations should be determined by the limit values of these parameters.
A characteristic defect of the rods: the weakening of the landing tips and the curvature of the rod rod.
The characteristic defects of the valves are wear of the working chamfers, curvature of the rod, the breakage of the valve plate, wear of the valve end
Characteristic defects of pushers are wear of the plate, the sink on the work surface, and the wear of the rod
Worn plates and pusher rods are restored by chrome plating.
After restoration, the valves are lapped in the seats of the cylinder heads.