The structure of a car engine (VAZ-2109)

The cars are equipped with four-cylinder, four-stroke carburetor engines of various cylinder volumes, with in-line cylinder arrangement and with a camshaft located on the cylinder head. The engine is specially designed for transverse placement on a front-wheel drive car. Therefore, its layout and main dimensions are chosen so that it, together with the gearbox, can be placed transversely between the mudguards of the front wheels.

Three unified engines with a working volume of 1100, 1300 and 1500 cm³ are formed by a combination of three blocks of different height and cylinder diameter, two cylinder heads with different diameter intake channels, as well as two pistons of different diameters (76 and 82), and two crankshafts with crank radii corresponding to piston strokes of 60.6 and 71 mm.

When assembled with the gearbox and clutch, the engine forms a single rigid unit - the power unit. It is installed on the car on three elastic supports. They take both the weight of the power unit and the loads that occur when the car starts moving, accelerates and brakes. The elastic supports absorb vibrations of the running engine and do not transmit them to the body, thereby reducing noise in the car. On the other hand, the elastic supports protect the power unit from sharp impacts when the car is moving on uneven roads.

The car has a three-point mounting scheme for the power unit, consisting of front, rear and left supports. The front and left supports have the same design and consist of an outer steel collar and an inner aluminum bushing, between which there is rubber vulcanized to them.



The rear support is bolted from below to the body bottom. It consists of external steel reinforcement and an internal aluminum bushing, also separated by rubber. The rear suspension bracket is steel, forged, and is attached to the gearbox with bolts connecting the clutch housing to the gearbox housing.

Cylinder block

All engine cylinders are combined together with the upper part of the crankcase into one common unit - the cylinder block, cast from special high-strength cast iron. This arrangement ensures structural strength, rigidity, compactness and reduces engine weight. Coolant ducts are made along the entire height of the cylinder block, which improves the cooling of the pistons and piston rings and reduces deformation of the cylinder block from uneven heating.

The block cylinders are divided into five classes by diameter, each with a 0.01 mm increment, designated by the letters A, B, C, D, E:

Class	Cylinder diameter of engines 21081, 2108, mm	Engine cylinder diameter 21083, mm
A	76,000-76,010	82,000-82,010
IN	76,010-76,020	82,010-82,020
WITH	76,020-76.030	82,020-82,030
D	76,030-76,040	82,030-82,040
E	76,040-76,050	82,040-82,050

The cylinder class is indicated on the lower plane of the block opposite each cylinder. The cylinder and the piston mating with it must be of the same class. During repair, the cylinders can be bored and honed to increase the piston diameter by 0.4 and 0.8 mm.

The lower part of the cylinder block contains five main bearing supports of the crankshaft with thin-walled steel-aluminum liners. The upper and lower liners of the middle (3rd) main bearing are without a groove on the inner surface. The upper liners of the remaining supports have a groove on the inner surface, and the lower ones do not have a groove. Until 1988, the lower liners of these bearings also had grooves.


The bearings have removable covers 2, which are attached to the cylinder block with self-locking bolts. The holes for the crankshaft bearings in the cylinder block are machined together with the covers, which ensures high precision, the correct geometric shape of the holes and their alignment. Therefore, the bearing covers are not interchangeable and have marks on the outer surface to distinguish them (see figure 6).


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The middle support has sockets for installing thrust half rings 12 (see figure 6). holding the crankshaft from axial movements. A metal-ceramic half ring is placed on the rear side of the middle support (yellow color), and on the front side - steel-aluminum.

The axial clearance of the crankshaft should be 0.06-0.026 mm. If the clearance exceeds the maximum allowable (0.35 mm), it is necessary to replace the half rings with repair ones, increased by 0.127 mm. It should be borne in mind that the grooves located on one side of the half rings should face the thrust surfaces of the crankshaft.

The cylinder block is closed from below by a stamped steel crankcase 37. The crankcase has a partition to calm the oil. A gasket made of a cork-rubber mixture is installed between the oil crankcase and the cylinder block.

The clutch housing is attached to the rear end of the cylinder block. The exact positioning of the housing relative to the cylinder block and the alignment of the crankshaft and the primary shaft of the gearbox is ensured by two centering bushings pressed into the cylinder block.

Cylinder head

Cylinder head 27 is common for four cylinders. It is cast from aluminum alloy and has wedge-shaped combustion chambers. Valve guide bushings and seats made of cast iron are pressed into the head. The seats, pre-cooled in liquid nitrogen, are inserted into the seats of the heated cylinder head. This ensures a reliable and strong fit of the seats in the head.

A special non-shrinking gasket on a metal frame is installed between the head and the cylinder block. The head is centered on the cylinder block with two bushings and is attached to it with ten bolts.


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To ensure uniform compression of the entire surface of the cylinder head gasket, to ensure reliable sealing and to eliminate subsequent tightening of the bolts during vehicle maintenance, the cylinder head mounting bolts are tightened uniformly without jerking in four steps and in a strictly defined sequence (see figure 7):

• step 1 - tighten the bolts to a torque of 2 kg cm;
• step 2 - tighten the bolts to a torque of 7.08-8.74 kg cm,
• step 3 - turn the bolts 90°;
• step 4: Turn the bolts 90° again.

In the upper part of the cylinder head there are five supports for the journals of the camshaft 17. The supports are made detachable. The upper half is located in the bearing housings 16 and 21 (front and back), and the lower one is in the cylinder head. The mounting bushings of the camshaft bearing housings are located at the housing mounting studs. The holes in the supports are machined together with the bearing housings, so they are not interchangeable, and the cylinder head can only be replaced together with the bearing housings.

On the cylinder head surfaces mating with the bearing housings, in the area of the extreme camshaft supports, apply a sealant of the KLT-75TM type. Install the bearing housings and tighten their fastening nuts in two steps.

• 1st step - pre-tighten the nuts in the sequence indicated on sheet 7 until the bearing housing surfaces are flush with the cylinder head, making sure that the housing mounting bushings fit freely into their sockets;
• 2nd step - finally tighten the nuts to a torque of 2.2 kg/cm in the same sequence.

Valve timing. During one working cycle, four strokes occur in the engine cylinder - intake of the combustible mixture, compression, power stroke and exhaust of exhaust gases. These strokes are performed in two crankshaft revolutions, i.e. each stroke occurs in half a revolution (180°) of the crankshaft.

The intake valve begins to open ahead of time, i.e. before the piston approaches the top dead center (TDC) at a distance corresponding to 33* crankshaft rotation before TDC. This is necessary so that the valve is fully open when the piston goes down, and as much fresh combustible mixture as possible enters through the fully open intake port.

The intake valve closes with a delay, i.e. after the pistons have passed the bottom dead center (BDC) at a distance corresponding to 79' of crankshaft rotation after BDC. Due to the inertial pressure of the stream of sucked-in combustible mixture, it continues to enter the cylinder when the piston has already begun to move upward, and thus better filling of the cylinder is ensured. Thus, intake practically occurs during the crankshaft rotation by 292°.

The exhaust valve begins to open before the working stroke is completely finished, before the piston approaches BDC at a distance corresponding to 47° of crankshaft rotation before BDC. At this point, the pressure in the cylinder is still quite high, and gases begin to flow out of the cylinder intensively, causing their pressure and temperature to drop rapidly. This significantly reduces engine work during exhaust and protects the engine from overheating.

The exhaust continues even after the piston has passed TDC, i.e. when the crankshaft has turned 17° after TDC. Thus, the exhaust duration is 244°.

It is clear from the phase diagram that there is a moment (50° of crankshaft rotation near TDC) when both valves are open simultaneously - the intake and exhaust. This position is called valve overlap. Due to the short time interval, valve overlap does not lead to the penetration of exhaust gases into the intake manifold, but on the contrary, the inertia of the exhaust gas flow causes the combustible mixture to be sucked into the cylinder and thus improves its filling.

The described valve timing phases take place with a gap of A between the camshaft cam and the valve tappet on a cold engine.

To ensure that the valve opening and closing times are coordinated with the crankshaft rotation angles (i.e. to ensure the correct installation of the valve timing), there are marks on the engine parts (see figure 7) 7 - on the rear cover of the toothed belt; 8 - on the camshaft pulley; 10 and 11 - on the front cover of the toothed belt; 12 - on the generator drive pulley; 13 - on the oil pump cover; 14 - on the toothed pulley of the crankshaft.

If the valve timing is set correctly, then when the piston of the first cylinder is at TDC at the end of the compression stroke, mark 7 on the rear cover of the toothed belt should coincide with mark 8 on the camshaft pulley, and mark 14 on the toothed pulley of the crankshaft should coincide with mark 13 on the oil pump cover.

When the camshaft drive cavity is closed by the front cover, the crankshaft position can be determined by the marks on the generator drive pulley and the front toothed belt cover. When the piston of the fourth cylinder is in TDC, mark 12 on the pulley should coincide with mark 11 on the camshaft drive cover. In addition, you can use mark 20 (see figure 6) on the flywheel and scale 19 in the clutch housing hatch. One division of the scale corresponds to a crankshaft rotation of 1°. When the marks coincide, the belt tension and clearances A in the valve mechanism are adjusted.

Engine operating order

For smooth operation of a multi-cylinder engine and reduction of uneven loads on the crankshaft, the working processes in different cylinders must occur in a certain sequence (order). The order of operation of the engine cylinders depends on the location of the crankshaft journals and camshaft cams and for engines of the 2108 family is 1-3-4-2.

The sequence of alternating strokes in the engine cylinders over two full revolutions can be easily traced using the table:

Crankshaft half-turns (deg.)	Cylinders
	1	2	3	4
1st (180°)	working stroke	release	compression	inlet
2nd (360°)	release	inlet	working stroke	compression
3rd (540°)	inlet	compression	release	working stroke
4th (720°)	compression	working stroke	inlet	release

When the piston in the first cylinder moves down in the range from 0° to 180° of rotation, combustion and expansion of gases occurs. During expansion, gases perform useful work, so this stroke is called the power stroke. The third cylinder lags behind the first by 180°, and in it the piston moves up, compressing the working mixture. In the fourth cylinder, lagging behind the first by 360°, and behind the third by 180°, the piston moves down, and the combustible mixture is admitted. And finally, in the second cylinder, lagging behind the first cylinder in the cycle of the working process by 540°, the piston moves up at this time, and the exhaust gases are released. Similarly, in the range from 180° to 360° of rotation of the first crank pin, the power stroke occurs in the third cylinder, compression - in the fourth, intake - in the second and exhaust in the first, etc.