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T Maintenance of the gas distribution mechanism of the DT-75 tractor (and modifications - DT-75M, DT-75B, DT-75K) is reduced to adjusting the clearances of the mechanism, as well as checking the tightness of the valves.
Have increasing the gap between the rocker arm and the end face of the valve stem leads to valve knocking. Reducing the clearance, which is caused by incomplete adherence of the valves, leads to burning of the chamfers of the exhaust valves, jamming of the valve stems in the guide bushings. As a result, the engine power decreases, and the specific fuel consumption increases. The clearance between the rocker arm and the end of the valve stem on a cold engine (for tractors DT-75, DT-75M, DT-75B, DT-75K) for inlet and outlet valves is 0.25-0.3 mm.
NS checking and adjusting the gap is carried out according to the following algorithm:
1) - raise the sidewalls of the hood upper shield;
2) - remove the cover of the cylinder head cover (it must first be cleaned of dirt);
3) - turn on the decompression mechanism;
4) - using the handle, turn the crankshaft until the piston of the first cylinder reaches the TDC. (top dead center) at the end of the compression stroke, with both valves closed in the first cylinder. To install the piston in the vmt. a dowel pin is used which is screwed into the flywheel housing. First, the dowel pin must be unscrewed from the crankcase, and then inserted with the continuous end into the same hole and the flywheel turned until the pin enters the flywheel hole;
5) - after turning off the decompression mechanism, check the gap with a feeler gauge and, if necessary, adjust it using the rocker arm adjusting screw. Adjustment of the gaps between the rocker arm and the ends of the valve stems of the remaining cylinders should be carried out in accordance with the order of operation of the cylinders - 1-3-4-2;
6) - to adjust the clearances in each subsequent cylinder, turn the crankshaft half a turn;
7) - after the adjustment of the valve clearances in the same cylinder with the piston in the TDC, the decompression mechanism is adjusted. To do this, set the decompressor roller to the on position. Then select with the adjusting screw (36) [Fig. 1] the gaps between the rocker arm and the screw, the rocker arm and the valve, and then unscrew the screw (36) one turn and lock it in this position;
8) - after completing the adjustment of the gaps, replace the hood cover and close the side screws of the hood upper shield.
Rice. 1. The gas distribution mechanism of the DT-75M tractor.
1) - Flange;
2) - Key;
3) - Washer;
4) - Bolt;
5) - Gear;
6) - Bushing;
7) - Movie;
8) - Plug;
9) - Bracket;
10) - Cylinder head;
11) - Roller;
13) - Stand;
14) - Bracket;
15) - Spring;
16) - Croutons;
17) - Plate;
18) - Spring;
19) - Spring;
20) - Plate;
21) - Bushing;
22) - Exhaust valve;
23) - Saddle;
24) - Inlet valve;
25) - Tip;
26) - Camshaft;
27) - Heel pad;
28) - Pusher;
30) - Bracket;
31) - Barbell;
32) - Tip;
33) - Adjusting screw;
34) - Cover;
36) - Screw;
37) - Rocker.
NS Checking the tightness of the valves to the cylinder head sockets, as well as grinding the valves (if necessary) is carried out during TO-3 after 960 hours of engine operation.
H To carry out the grinding of the valves, it is necessary to remove the cylinder head and disassemble the valve mechanism. To grind the valves, a paste is used, which includes a mixture of M14 or M20 micropowder with diesel oil. The valves are rubbed in until an even matte annular strip is formed (strip width from 1.5 mm).
NS Checking the tightness of the valves is carried out at the end of the assembly of the valve mechanism by pouring kerosene into the inlet channels of the valves. There should be no leakage within 3 minutes.
NS When replacing the old valve, it is necessary to ensure that the new one sinks relative to the plane of the cylinder head after lapping at least 1.6 mm (for the exhaust valve) and 1.1 mm (for the intake valve).
Z the tightening of the cylinder head fastening nuts should be carried out evenly (in several steps) in accordance with the sequence indicated in the diagram [Fig. 2].
Rice. 2. Diagram of a tightening of the cylinder head nuts. Tractors DT-75, DT-75M, DT-75B, DT-75K.
Z and in one step, the nut should be tightened by 1-2 faces. Tightening torque 16-18 kgf m (160-180 N.m).
R Adjustment of the axial movement of the camshaft is carried out when the upper shoulder of the front camshaft bearing bushing is worn by selecting shims, which are installed on the flange (1) [Fig. 1].
How do the valves of the A-41 engine regulate?
When checking and adjusting the gaps between the rocker arm strikers and the valve stems, the following rules are followed:
Free and convenient access to the valve mechanism is prepared - for this, the sidewalls and the top sheet of the hood are removed.
Clean the dust and remove the cylinder head cap.
Check the tightness of the nuts (valve rocker struts and cylinder head fastening to the block) in order to establish the correct valve clearances.
The decompression mechanism is turned on and the engine crankshaft is slowly rotated until the intake and exhaust valves of the first cylinder are completely closed (while both rocker arms of the valves should swing freely by the amount of clearance between the strikers and the valve stems).
Unscrew the set screw from the flywheel housing and insert it into the same hole with an uncut part. Then, pushing down on the screw, crank the engine crankshaft until the set screw fits into the recess on the flywheel. In this case, the piston of the first cylinder is set to position b. m. t. compression stroke.
The decompression mechanism is turned off and the gaps between the rocker arms and the valve stems are checked with a probe.
It should be borne in mind that checking and adjusting valve clearances when the decompression mechanism is on will lead to incorrect results that disrupt the normal operation of the valve mechanism. With properly adjusted valves, the clearances (on a cold engine) should be within 0.25-0.30 mm.
If the valve clearances do not correspond to the specified value, adjust them. To do this, release the lock nut of the adjusting screw, holding it with a screwdriver. Then, holding the lock nut with a wrench, unscrew the adjusting screw and install a 0.3 mm thick probe between the rocker arm and the valve stem. The adjusting screw is tightened so that the stylus moves with force. After that, holding the adjusting screw with a screwdriver, tighten its lock nut. Once again, check the gap on the probe, rotating the pusher rods (in order to make sure that the rod does not touch the block walls).
Thread the set screw into the threaded hole in the flywheel housing. Turn the engine crankshaft half a turn, setting the piston in the third cylinder to the position corresponding to the end of the compression stroke. Adjust the valve clearances in the third cylinder. With a further turn of the crankshaft by half a turn, the clearances in the fourth cylinder are adjusted, and then in the second.
After adjusting the valves, the decompression mechanism must be adjusted. To do this, install the roller of the decompression mechanism so that the adjusting screws are located vertically (with persistent tails to the rocker arms); unlock the adjusting screws; turn the adjusting screws, choosing the gaps - between the screws and rocker arms, valves and rocker arms; turn each adjusting screw one turn and lock them.
After completing the adjustment of the decompression mechanism, put the cylinder head cap in place, correctly laying the sealing gasket, and fix the cap. The operation is over. You can check the valve adjustment by starting the engine.
Quite often, during long-term operation of the dt-75 tractor, it is necessary to adjust the valves. In our case, the engine is a-41.
First of all, we unscrew the valve cover and remove it. First you need to check the tightness of the rocker shaft. How well they are attracted. Then we will set the first cylinder to a measured point, and adjust the valves.
In order to set a measured point, it is necessary that the intake exhaust valves first open and why they overlap one after the second. Then slowly rotates the crankshaft using the launcher. On the left side of the dt-75 tractor there is a hole on the clutch housing in the direction of travel.
In other words, we insert a pin there and slowly rotate the crankshaft and the pin should go into the holes on the flywheel. This will indicate the top measured point of the first cylinder.
Then we adjust the valve in order. The allowable clearance is 0.25-0.30 millimeters for both intake and exhaust valves.
The principle of valve adjustment on the dt-75 tractor.
We loosen the nut as shown in the figure.
Then, using a screwdriver, rotate the nut clockwise the same, thereby reducing the gap.
We take a 0.3 millimeter dipstick and it should be pulled through with little effort. After adjusting the valve, hold the adjusting screw with a screwdriver and tighten the fixing nut. Then we check with a feeler gauge to see if the gap is out of order. This operation must be carried out on all valves of the dt-75 tractor.
72 73 74 75 76 77 78 79..ADJUSTMENT OF VALVE AND DECOMPRESSION MECHANISMS OF A-01, A-01M and A-41 DIESELS
In the valve mechanism, the gap between the end of the valve stem and the rocker arm is adjusted. This clearance is necessary for a snug fit of the valve in the seat in the cylinder head and to compensate for the thermal expansion of the valve drive mechanism parts during engine operation.
The gap A (see Fig. 14) between the rod of the inlet and outlet valves and the rocker arm is set the same within
0.25-0.30 mm. With a larger clearance, the valve timing is shifted, the filling and cleaning of the cylinders deteriorate, shock loads and wear of the valve timing mechanism parts increase, and the valve stem may even break. With a smaller clearance, the valve fits loosely into the seat. As a result, the tightness of the combustion chamber is compromised, the compression of the engine decreases, it is difficult to start, the engine overheats and does not develop full power.
Incomplete closing of the valves leads to burnout of the working chamfers due to the breakthrough of hot gases.
Checking and adjusting the clearance between the valve stem and the rocker arm
The clearance is checked both on a cold and on a hot engine, but not earlier than 15 minutes after stopping it. Check in this order:
turn off the fuel supply;
Clean the caps 7 (see Fig. 16) of the cylinder heads from ache. Unscrew the nuts 13 for fastening the caps, detach the decompression mechanism activation lever and remove the caps;
Check the tightening of the nuts securing the struts 11 of the axis of the rocker arms and the nuts securing the cylinder head to the block;
Use a screwdriver or wrench to set the decompression mechanism to the on position to facilitate cranking of the crankshaft;
Observing the rocker arms of the valves of the first cylinder, slowly rotate the crankshaft clockwise with the handle until both valves (exhaust and then intake) open and close, which corresponds to the initial period of the compression stroke. Unscrew the set screw from the hole in the flywheel housing and insert it with the unthreaded part into the same hole until it stops in the flywheel disk;
Pressing the set screw by hand, continue to turn the crankshaft until the screw enters the recess on the flywheel disk; in this position of the crankshaft, the piston of the first cylinder is at. m. t. after the compression stroke;
The decompression mechanism is turned off and the gap between the rod and the rocker arm of the inlet and outlet valves of the first cylinder is checked with a probe.
If necessary, the gap is adjusted.
To adjust the gap, you must:
Loosen the lock nut 12 (see Fig. 14) of the adjusting screw 1.3 on the rocker arm, holding the adjusting screw with a screwdriver;
Insert a 0.25 mm thick gauge plate into the gap and, turning the adjusting screw with a screwdriver, set the required gap;
While holding the screw with a screwdriver, tighten the lock nut and check the clearance by turning the push rod by hand to make sure it does not bind. With a properly adjusted gap, the 0.25 mm stylus should enter with light pressure, the 0.30 mm stylus with force.
Decompression mechanism adjustment
At the end of the clearance adjustment in the valves of the first cylinder, the decompression mechanism in this cylinder is adjusted in the following order:
Include the decompression mechanism, set the roller 8 so that the axis of the adjusting screws 7 is vertical; loosen the tightening of the adjusting screw locknut; the uncontrolled adjusting screw selects the gaps between it and the back of the rocker arm, the valve stem and the rocker arm;
Turn the adjusting screw one turn clockwise, while the valve opens slightly;
The adjusting screw, holding it with a screwdriver, is counterbalanced with a nut.
At the end of the adjustment of the decompression mechanism of the first cylinder, screw the set screw with the threaded part into the hole in the flywheel housing.
With further cranking of the crankshaft clockwise, the valve and decompression mechanisms in the next engine are adjusted accordingly.
For A-01 engines and its modifications, the crankshaft is turned after 120 ° (1/3 turn), for A-41 engines and its modifications through 180 ° (1/2 turn), which will correspond to the end of the compression stroke in each subsequent cylinder (taking into account the order of operation of the cylinders).
It should be borne in mind that the intake and exhaust valves must be closed before adjusting the clearances. In this position, they are checked by turning the barbells by hand.
After adjusting the valve and decompression mechanisms, the engine is started, if the knock of the valves is heard, the engine is stopped and the clearance is checked again.
At the end of the adjustment, the cylinder head caps are installed in place, observing the correct laying of the gaskets 6 (see Fig. 16). Oil leakage is not allowed in the places where the caps adhere to the cylinder heads.
