The main dimensions of the connecting rod-piston group are shown in Figure 1.

The piston is cast aluminum. During manufacture, the mass of the pistons is strictly maintained.

Therefore, when assembling the engine, it is not required to select pistons of the same group by weight.

Ремонт ШПГ двигателя ВАЗ-2123

According to the outer diameter, the pistons are divided into five classes (A, B, C, D, E) every 0.01 mm. The outer surface of the piston has a complex shape.

It is barrel-shaped in height, and oval in cross-section.

Therefore, it is only necessary to measure the piston diameter in a plane perpendicular to the piston pin, at a distance of 55 mm from the piston crown.

According to the diameter of the bore for the piston pin, the pistons are divided into three classes (1, 2, 3) every 0.004 mm.

Classes of piston diameters and bores for the piston pin are stamped on the piston crown

Ремонт ШПГ двигателя ВАЗ-2123Места, на которых допускается удалять металл, при подгонке массы верхней и нижней головок шатуна

Figure 2. Marking of the piston and connecting rod

Oversized pistons are manufactured with an outer diameter increased by 0.4 and 0.8 mm.

The piston bottoms are marked with a triangle or square.

The triangle corresponds to an increase in the outer diameter by 0.4 mm and the square to 0.8 mm.

The arrow on the piston crown shows how to correctly orient the piston when it is installed in the cylinder. It should point towards the camshaft drive.

Piston pin - steel, hollow, floating type, the father-in-law rotates freely in the piston bore and the connecting rod bushing. The pin is held in the piston by two steel retaining rings.

According to the outer diameter, the fingers are subdivided into three classes every 0.004 mm. The class is marked with paint at the end of the finger: the blue mark is the first, the green is the second, and the red is the third class.

Piston rings - made of cast iron. The upper compression ring has a chrome-plated barrel-shaped outer surface.

Scraper-type lower compression ring. Oil scraper ring - with chrome-plated working lips and with an expanding coil spring (expander).

On rings of repair dimensions, a digital marking "40" or "80" is put, which corresponds to an increase in the outer diameter by 0.4 or 0.8 mm.

The connecting rod is steel, forged. The connecting rod is machined together with the cover and is therefore not individually interchangeable.

In order not to confuse the covers and connecting rods during assembly, the number 6 (see Figure 2) of the cylinder in which they are installed is stamped on them.

When assembling, the numbers on the connecting rod and the cover must be on the same side

A steel-bronze bushing is pressed into the upper head of the connecting rod.

According to the bore diameter of this bushing, the connecting rods are divided into three classes every 0.004 mm (the same as the pistons).

Class number 5 is stamped on the upper connecting rod head.

By the weight of the upper and lower heads, the connecting rods are divided into classes (table), marked with paint on the connecting rod.

The engine must be fitted with connecting rods of the same weight class.

The weight of the connecting rods can be adjusted by removing metal from the bosses on the heads to a minimum size of 16.5 and 35.5 mm (Figure 3).

Classes of connecting rods by weight of the upper and lower heads

weight of connecting rod heads g.

 

Class

Marking

color

top

bottom

 

 

186±2

 

519±3

А

white

525±3

В

blue

531±3

С

red

 

190±2

 

519±3

D

black

525±3

Е

purple

531±3

F

green

 

194±2

 

519±3

G

yellow

525±3

H

brown

531±3

I

orange

Since 2012, the masses of the connecting rod heads have changed slightly.

weight of connecting rod heads g.

 Class

Marking color

top

bottom

 

 

186±2

 

527±3

А

white

533±3

В

blue

539±3

С

red

 

190±2

 

527±3

D

black

533±3

Е

purple

539±3

F

green

 

194±2

 

527±3

G

yellow

533±3

H

brown

539±3

I

orange

Selection of the piston to the cylinder

The calculated minimum clearance between the piston and the cylinder (for new parts) is 0.025-0.045 mm.

It is defined as the difference between the minimum cylinder size and the maximum piston size and is provided by installing pistons of the same class as the cylinders.

The maximum allowable clearance (with wear of parts) is 0.15 mm.

If the clearance of a used engine exceeds 0.15 mm, then the pistons must be re-matched to the cylinders so that the clearance is as close as possible to the calculated one.

Spare parts are supplied with pistons of classes A, C, E.

These classes are sufficient for matching a piston to any cylinder when repairing an engine, since pistons and cylinders are divided into classes with a slight overlap of sizes.

For example, class B and D cylinders can be matched with a class C piston.

Disassembly and assembly

Disassembly

Remove the piston pin retaining rings from the piston, remove the pin and disconnect the connecting rod from the piston. Remove the piston rings.

The connecting rod bolts are pressed into the connecting rod. Therefore, in order not to disturb the landing of the bolt in the connecting rod, it is not allowed to press out the bolts from the connecting rods when disassembling the engine and the connecting rod-piston group.

If some parts of the connecting rod-piston group are not damaged and slightly worn, then they can be reused. Therefore, mark them when disassembling in order to later assemble a group with the same parts and install them in the old engine cylinder.

Assembly

Match the pin to the piston and connecting rod prior to assembly. On new parts, the pin hole class in the connecting rod and piston must be identical to that of the pin.

For used parts, for correct mating, it is necessary that the piston pin, lubricated with engine oil, enters the hole of the piston or connecting rod by simply pressing the thumb of the hand (Figure 4) and does not fall out of it if you hold the piston as shown in Figure 5.

Ремонт ШПГ двигателя ВАЗ-2123

Ремонт ШПГ двигателя ВАЗ-2123

Figure 4. Installing the piston pin

Figure 5. Checking the seating of the piston pin

Replace the drop-down finger with another, of the following category. If a third category pin was inserted into the piston, replace the piston pin and connecting rod.

The assembly of the connecting rod-piston group is carried out in the reverse order of disassembly. After installing the piston pin, lubricate it with engine oil through the holes in the piston pin bore.

Install the piston rings in the following order.

Lubricate the grooves on the piston and piston rings with engine oil.

Orient the piston rings so that the upper compression ring lock is at a 45˚ angle to the piston pin axis, the lower compression ring lock at approximately 180˚ to the upper compression ring lock axis, and the oil wiper lock at approximately 90˚ to the lock axis upper compression ring

Install the lower compression ring with the groove down (see figure 1). If the ring is marked "Top" or "TOP", then set the ring with the mark up (to the bottom of the piston).

Before installing the oil scraper ring, check that the joint of the spring expander is on the opposite side of the ring joint.

Disassembly and assembly of the connecting rod-piston group can be viewed here.Repair of the VAZ-2123 engine

Checking the technical condition

Remove carbon deposits from the piston and remove all deposits from the piston and connecting rod oil passages.

Inspect the details carefully.

Cracks of any nature on the piston, piston rings, pin, on the connecting rod and its cover are not allowed.

If there are deep marks on the working surface of the liners, replace the liners with new ones.

Check the clearance between the piston rings and grooves with a set of feelers, as shown in Figure 6, by inserting the ring into the corresponding groove.

The design clearance (rounded to 0.01 mm) for new parts is 0.04-0.07 mm for the upper compression ring, 0.03-0.06 mm for the lower compression ring and 0.02-0.05 mm for the oil scraper ... The maximum allowable wear clearances are 0.15 mm.

Ремонт ШПГ двигателя ВАЗ-2123

Ремонт ШПГ двигателя ВАЗ-2123

Figure 6. Checking the clearance between piston rings and grooves

Figure 7. Checking the clearance in the ring joint

Check the clearance in the piston ring lock with a set of feeler gauges by inserting the rings into a gauge (Figure 7) with a hole diameter equal to the nominal ring diameter with a tolerance of 0.003 mm.

For normal-size rings with a diameter of 82 mm, caliber 67.8125.9502 can be used.

The gap should be between 0.25-0.45 mm for all new rings. The maximum allowable wear clearance is 1 mm.