Open large image in new tab »
Pic. 9. Gas distribution mechanism: 1. Pulley on the crankshaft to drive the generator; 2. Toothed pulley on the crankshaft to drive the camshaft; 3. Camshaft timing belt; 4. Coolant pump pulley; 5. Tension roller; 6. Eccentric axis of the tension roller; 7. Installation mark (tendril) on the back cover of the toothed belt; 8. Alignment mark on the camshaft pulley; 9. Camshaft pulley; 10. 5°spark advance mark on timing belt front cover; 11. Ignition advance mark by 0°; 12. TDC mark on the alternator drive pulley; 13. Mounting mark on the cover of the oil pump; 14. TDC mark on the crankshaft sprocket; 15. Front camshaft bearing housing; 16. Rear camshaft bearing housing; 17. Eccentric on the camshaft to drive the fuel pump; 18 Camshaft; 19. Valve crackers; 20. Valve plate; 21. Outer valve spring; 22. Internal valve spring; 23. Support washer springs; 24. Inlet valve; 25. Valve guides; 26. Exhaust valve; 27. Retaining ring; 28. Oil cap; 29. Valve lifter; 30. Adjusting washer; 31. Cylinder head; 32. Valve seat; 33. Distance ring; I. Checking the belt tension; II. The procedure for tightening the cylinder head bolts; III. The order of tightening the nuts of the camshaft bearing housings.
The gas distribution mechanism ensures that the engine cylinders are filled with a fresh charge of the combustible mixture and the exhaust gases are released in accordance with the requirements of the working process in each of the engine cylinders. This mechanism is characterized by an upper in-line arrangement of valves.
The camshaft 18, which controls the opening and closing of the valves, is located in the cylinder head and is driven from the crankshaft by a toothed belt 3. The valves are driven directly by the camshaft cams through cylindrical pushers 29 without intermediate levers. There is a washer 30 in the pusher seat, by selecting which the clearance in the valve mechanism is adjusted.
An elastic toothed belt also drives the pulley 4 of the coolant pump. Roller 5 serves to tension the belt. It rotates on an eccentric axle 6 attached to the cylinder head. By turning the axis 6 relative to the fastening stud, the belt tension is changed. The belt tension is considered normal if, in the middle part of the branch between the pulleys of the camshaft and crankshaft, the belt is twisted with a finger force of 1.5-2 kgf.
Due to the strict orientation of the keyways in the driving 2 and driven 9 pulleys relative to the teeth and their corresponding engagement with the toothed belt, the required valve timing is provided. Checking the correct relative position of the drive pulleys is carried out as follows: the crankshaft rotates to a position in which the piston of the first cylinder is at TDC of the compression stroke (both valves are closed and the mark on the crankshaft pulley is aligned with mark 13 on the oil pump cover). In this case, mark 8 must coincide with mark 7 on the back cover of the toothed belt, and the mark on the flywheel must be opposite the middle division of the scale on the clutch housing.
If the marks do not match, then loosen the belt with a tension roller, remove it from the camshaft pulley, correct the position of the pulley, put the belt back on the pulley and slightly tighten the tension roller. Again, check the coincidence of the alignment marks by turning the crankshaft two turns clockwise.
It is not allowed to turn the crankshaft and camshafts of engines 2108 and 21081 if the camshaft drive belt is not installed, because. pistons at TDC will hit the valves and engine parts will be damaged. In addition, the crankshaft can only be turned over the side of the generator drive pulley and only in the direction of tightening the bolt (clockwise). It is not allowed to turn the crankshaft by the camshaft pulley or by the bolt of its fastening.
The cast iron camshaft has five bearing journals that rotate in sockets made in the cylinder head and in camshaft bearing housings 15 and 16. On the shaft there is an eccentric 17 for driving the fuel pump. The rear end of the camshaft has a groove for connection to the engine ignition distributor.
The camshaft is held from axial movements by a shaft thrust shoulder located between the end of the rear shaft support and the auxiliary unit housing. To increase wear resistance, the working surfaces of the cams, the eccentric and the surface under the oil seal are bleached. The depth of the bleached layer is not less than 0.2 mm.
valves (intake 24 and exhaust 26), which serve to periodically open and close the openings of the intake and exhaust channels, are located obliquely in a row in the cylinder head.
The inlet valve is made of chrome silicon steel. Its head has a larger diameter for better filling of the cylinder. The exhaust valve is made of composite: the stem is made of chromium-nickel-molybdenum steel with better wear resistance to friction and good thermal conductivity to remove heat from the valve head to its guide sleeve, and the head is made of heat-resistant chromium-nickel-manganese steel. In addition, the working chamfer of the exhaust valve, which operates at high temperatures in an aggressive exhaust gas environment, has a heat-resistant alloy overlay
The valve guide bushings are made of cast iron, pressed into the cylinder head and are kept from possible falling out by retaining rings 27. The holes in the bushings are finished assembled with the cylinder head, which ensures a narrow tolerance for the hole diameter and the accuracy of its location in relation to the working chamfers of the seat and valve. The bores of the guide bushings have spiral grooves for lubrication. The inlet valve bushings are grooved up to half the bore length, and the exhaust valve bushings are grooved along the entire length of the bore.
From above, caps 28 made of fluororubber rubber with a steel reinforcing ring are put on the guide bushings, which cover the valve stem and serve to reduce the penetration of oil into the combustion chamber through the gaps between the guide bush and the valve stem.
Springs (outer 21 and inner 22) press the valve to the seat and do not allow it to come off the actuator. The lower ends of the springs rest on the support washer 23. The upper support plate 20 of the springs is held on the valve stem by two crackers 19, which, when folded, have the shape of a truncated cone. The crackers have three inner collars that fit into grooves on the valve stem. This design provides both a secure connection and rotation of the valves during operation, so that they wear more evenly.
Pushers 29 are designed to transfer force from the camshaft cams to the valves. The pushers are made in the form of cylindrical cups and are located in the guides of the cylinder heads. An adjusting washer 30 of a certain thickness is placed in the end recess of the pusher, providing the necessary clearance between the camshaft cam and the pusher with the washer.
The washers are made of 20X steel and subjected to nitrocarburizing to increase the surface hardness. Spare parts are supplied with shims with a thickness of 3 to 4.5 mm at intervals of every 0.05 mm. The washer thickness is marked on its surface. The washer must be installed in the pusher with the marking down.
When the engine is running, the pushers are constantly rotated around their axes, which is necessary for their uniform wear. The rotation of the pushers is achieved by shifting the cam axis relative to the pusher axis by 1 mm.