Crank mechanism and cylinder block (VAZ-2109)

The crank mechanism is used to convert the reciprocating motion of the piston into the rotational motion of the crankshaft. The mechanism consists of pistons with piston rings and pins, connecting rods, a crankshaft and a flywheel. The parts of the crank mechanism are located and operate in the cylinder block.

Cylinder block

All engine cylinders together with the upper part of the crankcase are combined into a common unit - the cylinder block, cast from special high-strength cast iron. This design allows for high rigidity and strength with a relatively small weight, since the force from the gas pressure in a separate cylinder is perceived by the entire cross-section of the cylinder block. It resists well the action of inertial forces and moments that arise from the moving parts of the crank mechanism. To increase rigidity, the cylinder block has five partitions with ribs and an increased thickness of the upper plate to which the cylinder head is attached.

The cylinders are located vertically in the block, in a row. They do not have any inserted liners and are bored directly in the cylinder block. To obtain a high degree of surface purity, the cylinder walls are honed.

For normal engine operation, the clearance between the piston and the cylinder must be within certain limits: 0.025...0.045 mm on a new engine and not exceed 0.15 mm for worn pistons and cylinders. To make it easier to obtain such a clearance when assembling the engine, the diameters of the cylinders and pistons are divided into five classes, designated by the Latin letters A, B, C, D, E, through 0.01 mm (figure 12). When assembling an engine, pistons of the same class are inserted into cylinders of a certain class, which guarantees the required clearance value. The class (letter) of the cylinder diameter is stamped on the lower plane of the cylinder block opposite each cylinder (figure 13).







The main dimensions of the 2108 engine cylinder block are shown in Figure 12. The 21081 engine cylinder block differs from the 2108 in its smaller height - 242...242.2 mm, and the 21083 cylinder block has a larger cylinder diameter compared to the 2108:

• A — 82.00...82.01 mm
• B — 82.01...82.02 mm
• C — 82.02...82.03 mm
• D — 82.03...82.04 mm
• E — 82.04...82.05 mm

The engine model number is cast into the top of the cylinder block on the left side.

The cylinder block is an expensive part. Therefore, in order to extend its service life, the possibility of repairing the cylinders is provided. The thickness of the walls allows boring and honing the cylinders to the repair dimensions of the pistons, increased by 0.4 and 0.8 mm. Boring is performed if the wear of the cylinders exceeds 0.15 mm or if there are burrs on their walls.


The lower part of the cylinder block contains five crankshaft main bearing supports, onto which thin-walled steel-aluminum liners are placed. The bearing holes are half-made in the cylinder block and half-made in the bearing caps. Each cap is attached to the cylinder block with two self-locking bolts. To ensure high precision, the bearing holes are finally machined together with the bearing caps. Therefore, the caps are not interchangeable: they cannot be swapped or moved from one cylinder block to another. To distinguish the main bearing caps, there is a marking in the form of marks on their outer side (figure 14).



When assembling the engine, the bearing caps must be installed in a strictly defined position: in the same position in which they were in the cylinder block when processing the holes in the supports. Therefore, in order not to accidentally turn the caps over, they are made asymmetrical. In relation to the sides of the cap, the axis of the half-hole in it is shifted by 1 mm to the left. Correctly installed caps should have marks on the left side of the engine (the side where the generator and starter are located).

Along the right side of the cylinder block, the main channel of the lubrication system is drilled. From it, five inclined channels go to the main bearings of the crankshaft and a vertical channel for supplying oil upwards, to the camshaft. On the right front side of the cylinder block, there is a flange for installing an oil filter. Channels go from the flange to the main channel of the lubrication system and to the oil pump, which is attached to the front end of the cylinder block. On the left side of the block, there is a lug with an opening for a nipple to which the crankcase gas suction hose is connected. The oil level indicator is also inserted into this nipple.

The cooling jacket of the cylinder block is common to all cylinders. Coolant passages are made along the entire height of the cylinders, which improves the cooling of the pistons and piston rings and reduces block deformations from uneven heating. In order to secure the cooling jacket rods when casting the cylinder block, there are six holes in its outer walls, which are then closed with steel cup-shaped plugs. The cooling jacket directly (without intermediate pipelines) connected to the coolant pump, located in the tide on the right side of the cylinder block. The cooling jackets of the block and cylinder head communicate through openings in the upper plane of the cylinder block.

On the left side of the cylinder block there are bosses with holes for fastening the generator and the bracket for the front suspension of the power unit. On the right side, in addition to the flange for the oil filter, there is another flange with four holes for fastening the cylinder block on the assembly stand. At the rear of the cylinder block there are two brackets, reinforced with ribs, for fastening the clutch housing. To center the cylinder block with the clutch housing, two installation bushings are inserted into the holes of the brackets.

Piston

The piston is one of the most stressed parts of the engine. It perceives the pressure of gases and transmits it to the crankshaft through the piston pin and connecting rod. The piston is cast from a high-strength aluminum alloy. It is light and conducts heat well to the cylinder walls. But aluminum has a high temperature coefficient of linear expansion. Therefore, in order to reduce the thermal expansion of the piston from heating by hot gases and eliminate the risk of it jamming in the cylinder, a heat-compensating steel plate is poured into the piston head above the hole for the pin.

The main dimensions of the piston, connecting rod, piston pin and piston rings of the 2108 engine are given in Figure 15. Just like the engine cylinders, the pistons are sorted into five classes by outer diameter: A, B, C, D and E. The difference in the diameters of the pistons of adjacent classes is 0.01 mm. The piston class (letter) is stamped on its bottom (figure 16).





Engines 2108 and 21081 have identical pistons, and engine 21083 has pistons and rings with an outer diameter increased by 6 mm. The piston number is cast on the inner side of its skirt.

The piston diameter can be measured to determine its class only in one place: in the plane perpendicular to the piston pin, at a distance of 51.5 mm from the bottom. In other places, the piston diameter is not nominal, since the outer surface of the piston has a complex shape. In cross-section, it is oval (the ovality of the piston head is up to 0.1 mm, and the skirt - up to 0.55 mm), and the smaller axis of the oval coincides with the axis of the piston pin. In height, both the skirt and the piston head have a conical shape and, in addition, the head diameter is 0.5 mm less than the skirt diameter. This shape allows for compensation for uneven expansion of the piston when heated by reducing its taper and ovality.

The outer surface of the piston skirt is not smooth, but has many annular microgrooves up to 14 µm deep. Such a surface promotes better running-in of the piston to the cylinder walls and reduces friction losses, since oil is retained in the microgrooves. The piston bottom is flat, with an oval recess forming part of the combustion chamber, and with small recesses for the valves. In the lower part of the piston pin bosses, there are holes for the passage of oil to the piston pin. To improve lubrication conditions, two longitudinal grooves 3 mm wide and 0.7 mm deep are made in the upper part of the pin holes, in which oil accumulates. In the area of the bosses, the height of the skirt is reduced to prevent the crankshaft counterweights from touching the piston.

The hole for the piston pin is offset from the axis of symmetry by 1.2 mm to the right side of the engine. Due to this, a moment of force acts on the piston, pressing it to the cylinder walls always in the same position. Therefore, there is no knocking of the piston on the cylinder walls when it passes through the top dead center. However, this requires that the piston be installed in the cylinder in a strictly defined position. When assembling the engine, the pistons are installed so that the arrow 1 (figure 16) on the piston bottom was directed towards the front of the engine.

Piston: the pin is inserted into the piston with a gap of 0.008...0.016 mm. To ensure that such a high-precision gap is obtained in mass production, pistons are sorted by the diameter of the hole for the piston pin and the pins by the outer diameter into three categories through 0.04 mm. The number (1,2,3) indicating the piston category, as well as the class, is stamped on its bottom (see figure 16). During engine assembly, the piston and pin are taken of the same category, which guarantees the required clearance. The correctness of their mating is checked by inserting an oiled pin into the piston. The pin should easily enter the piston by hand pressure and not fall out of it under its own weight.

The pistons in the engine must be identical in mass to reduce vibrations of reciprocating moving parts. During manufacturing at the plant, the maximum deviation of piston mass +5 g is strictly maintained. Therefore, when assembling 2108 engines, it is not necessary to select pistons of the same group by mass or adjust their mass) by removing excess metal.

Spare parts are supplied with pistons of nominal size of only three classes - A, C and E. This is enough to select a piston for each cylinder during engine repair, since pistons and cylinders are divided into classes with some overlapping sizes. For example, a piston of class C can fit cylinders of classes B and D. The main thing when selecting a piston is to ensure the necessary installation clearance (0.025...0.045 mm) between the piston and the cylinder.

In addition to nominal size pistons, spare parts also include repair pistons with an outer diameter increased by 0.4 and 0.8 mm. These pistons are intended for installation in repaired cylinder blocks, in which the cylinders are bored and honed to the next repair size. The bottoms of the repair pistons are marked with a square 2 (see figure 16) or a triangle. A triangle corresponds to an increase in the outer diameter of 0.4 mm, and a square - 0.8 mm.

Piston rings

Piston rings provide the necessary seal between the piston and the cylinder walls and conduct heat from the piston to its walls. They are pressed against the cylinder walls by their own elasticity and gas pressure. Three cast iron rings are installed on the piston - two compression rings (sealing) and one (lower) oil scraper, which prevents oil from entering the combustion chamber.

The upper compression ring operates under conditions of high temperature, aggressive combustion products and insufficient lubrication. Therefore, to increase wear resistance, its outer surface is chromed, and to improve running-in, it is made convex (barrel-shaped) forms.

The lower compression ring has a recess at the bottom to collect oil during the piston's downward stroke, performing the additional function of an oil-scraping ring. The surface of the ring is phosphated to increase wear resistance and reduce friction against the cylinder walls.

Oil scraper ring - with chromed working edges and with a groove on the outer surface, which collects oil removed from the cylinder walls. Then it flows through the slots in the ring into the piston groove and from there flows into the oil sump. A steel coil spring is installed inside the ring, which decompresses the ring from the inside and presses it against the cylinder walls.

Rings of repair sizes are manufactured (the same as pistons) with an outer diameter increased by 0.4 and 0.8 mm.

Piston pin

Piston pin made of steel tubular section with a wall thickness of 3.5 mm. To increase hardness and wear resistance, its outer surface is cemented and hardened with high-frequency currents. In the upper head of the connecting rod, the pin is installed with an interference fit of 0.010...0.042 mm. Such a press fit prevents it from axial movement in the piston.

According to the outer diameter, the pins are sorted into three categories through 0.004 mm, corresponding to the piston categories. The ends of the pins are painted in the corresponding color: blue - the first category, green - the second, red - the third.

Connecting rod

The engine connecting rod is a forged steel I-section. Its lower head is split, and the plane of the split is perpendicular to the axis of the connecting rod. The crankshaft connecting rod bearing liners are installed in this head.

The connecting rod is machined together with the cover. To avoid mixing up the covers during assembly, the connecting rod and the corresponding cover are stamped with the number of the 6th cylinder (see figure 16), into which they are installed. When assembling, the numbers on the connecting rod and cover must be on the same side. The cover of the lower connecting rod head is attached to the connecting rod with two bolts with self-locking nuts. For precise centering of the bolts, their outer surface and the hole in the connecting rod are machined with high precision, and there is a belt near the bolt head, with which the bolt is pressed into the hole.

Where the lower head of the connecting rod passes into the rod, there is a hole through which oil is sprayed onto the piston and cylinder walls. When assembling the connecting rod and piston group, the connecting rod must be positioned so that the hole on it and the arrow on the piston are directed in the same direction.

Connecting rods (the same as pistons) must have the same mass. The mass of the upper head is adjusted with a tolerance of ±2 g, and the lower head ±3 g. This is ensured by removing excess metal from the bosses on the upper head of the connecting rod and on the cover of the lower head. Thus, the total mass of the connecting rod is adjusted with a tolerance of ±5 g.

For all engines (2108, 21081 and 21083) identical connecting rods are installed. But they are not interchangeable with the connecting rods of old engines (type 2101-2103), since they are 15 mm shorter.

Crankshaft

The 2108 and 21083 engines are equipped with identical crankshafts. The 21081 engine, due to the shorter piston stroke, uses a different crankshaft, with a distance between the axes of the connecting rod and main journals reduced by 5.2 mm. The 21081 crankshaft can be distinguished by its overall dimensions and by the location of the lubrication holes on the connecting rod journals. In the 21081 crankshafts, these holes are offset by 3.7 mm from the axis in the direction from the main journals, and in the 2108 crankshafts - by 1.5 mm in the opposite direction from the axis (figure 17).



The crankshaft is the main power part of the engine, which takes the action of gas pressure and inertial forces. It is cast from high-strength special cast iron. To reduce deformations during engine operation, the shaft is made five-bearing and with a large overlap of the main and connecting rod journals. High fatigue strength is ensured by smooth transitions between the journals and cheeks and careful processing of stressed areas. High wear resistance of the shaft journals is achieved by a large diameter of the journals (due to this, specific loads in bearings are reduced) and surface hardening of the necks with high-frequency currents to a depth of 2...3 mm.

The crankshaft journals have counterweights cast in one piece with the shaft. They balance the centrifugal forces that arise during engine operation from the masses of the crankpin, as well as from parts of the connecting rod and piston. Due to this, the main bearings are relieved from the action of centrifugal forces and engine vibrations are reduced. In addition, to reduce vibrations, the crankshafts are balanced. Since this balancing is performed without a flywheel, both the crankshafts and the flywheels are interchangeable.
The crankshaft body is drilled with holes connecting the 1st, 2nd, 4th and 5th main journals with the connecting rod journals. Oil is supplied through these channels to lubricate the connecting rod bearings. The technological outputs of the channels are closed with cap-shaped steel plugs, which are pressed in and calked at three points.

The main dimensions of the crankshaft and bearing shells are shown in Figure 18. The main and connecting rod journals are machined with a high degree of frequency and precision, since the clearance between the journals and the shells must be within 0.02...0.07 mm for connecting rod journals and 0.026...0.073 mm for main journals, and the maximum permissible clearance during wear must not exceed 0.1 and 0.15 mm, respectively.

It is possible to regrind the crankshaft journals during repairs with a diameter reduction of 0.25; 0,5; 0.75 and 1 mm. The journals are ground if they are worn to a diameter that is 0.005 mm less than the minimum for a given crankshaft size, and also if the journal ovality is greater than 0.03 mm or there are burrs on them. The diameters of the repair dimensions of the journals are also shown in Figure 18.



The front and rear ends of the crankshaft are sealed with self-tightening rubber seals. The front seal is pressed into the oil pump cover, and the rear seal is installed in a holder that is attached to the cylinder block. Two drive pulleys of the belt drives are attached to the front end of the crankshaft. One pulley (toothed) serves to drive the camshaft and is mounted on a segment key. The other pulley transmits rotation to the generator. It is mounted on a pin pressed into the toothed pulley and is centered with a cylindrical belt. Both pulleys are secured with a bolt. In addition, the front end of the crankshaft drives the drive gear of the oil pump, which is fixed on the shaft with two flats.

Inserts

The main and connecting rod bearing liners of the crankshaft are thin-walled, bimetallic, with radial holes for the passage of oil. They are made of steel tape covered with a layer of antifriction alloy AMO1-20 (79% aluminum, 20% tin and 1% copper) 0.4...0.5 mm thick. Between the steel base and the alloy there is a thin layer of pure aluminum. The liners of each bearing consist of identical halves. They are held from turning by projections that enter the grooves of the connecting rod or main bearing.

The upper main bearing shells have grooves on the inner surface for the passage of oil to the connecting rod bearings. The lower shells have been installed without a groove since 1988; But until 1988 they also had a groove and were interchangeable with the upper bearings. Connecting rod bearings differ from the main bearings in diameter, thickness and the absence of grooves on the inner surface. Upper and lower connecting rod bearings are interchangeable.

Bearing liners are manufactured in both normal and increased thickness (see figure 18) under the crankshaft journals, ground down to 0.25; 0,5; 0.75 and 1 mm.

Thrust half rings

Thrust half rings are installed in the cylinder block sockets on both sides of the middle (third) main bearing. They absorb axial loads acting on the crankshaft and limit its axial movement. Half rings are manufactured both in normal thickness and increased by 0.127 mm (see figure 18). By selecting the thickness of the half rings, the axial free play of the crankshaft is regulated, which should be within 0.06...0.26 mm on a new engine and not exceed the maximum: permissible - 0.35 mm when worn.

The front and rear half rings are made of different materials. The half ring installed on the rear side of the 3rd bearing experiences increased loads from the clutch and is therefore made of powder material. This material is yellowish in color and consists of 87...90% copper, 9.5...10.5% tin and 0.5...1% carbon. A half ring made by pressing from such material is porous. It is impregnated with oil and resists frictional wear well.

The front half rings bear a smaller load and therefore, like the liners, are made of steel and aluminum, with an antifriction layer thickness on the end surface of 0.3...0.5 mm. On the side of the antifriction layer there are two vertical grooves for the passage of oil. This side of the half ring (both front and back) must face the thrust surfaces of the crankshaft.

Flywheel

Flywheel 12 (see figure 9) serves to ensure the uniformity of engine operation. It stores kinetic energy during working strokes in the cylinders and gives it to the crank mechanism during the other three strokes. It also takes the crankshaft out of dead points. The flywheel is cast from cast iron and has a steel toothed crown, which is pressed onto the flywheel while hot. The teeth of the crown are hardened by high-frequency currents to increase wear resistance and strength.

The flywheel is secured to the crankshaft flange with six self-locking bolts, under which one common washer is placed. It must be installed so that the mark (cone-shaped hole) near the rim was located opposite the crankpin of the fourth cylinder. The mark serves to determine the top dead center in the first and fourth cylinders. The flywheel is centered by a cylindrical protrusion on the crankshaft.

To create pulses in the top dead center sensor, a steel pin is pressed into the flywheel rim, and to adjust the ignition timing, there is a mark 2 (see figure 30).