The piston pin is installed with an interference fit in the upper head of the connecting rod and rotates freely in the piston bosses.

The engines are equipped with SMP pistons.

Remove the piston rings using the piston ring pliers.

Разборка, проверка шатунно-поршневой группы двигателя К4М

Fit the piston and connecting rod assembly to the prism (1) of tool Mot. 574-22 (see Fig. 1).

Align the piston pin with the pin exit hole in the prism (1).

Using a press, press out the piston pin using the tool (2) of tool Mot. 574-22.

After disassembling the connecting rod and piston group, it is necessary to carry out a series of measurements in order to reject

worn parts.

Main wear areas:

- piston rings: they are erased during operation, besides they wear out along the width in the piston groove - change the rings as a set with each disassembly and assembly. Do not change the rings more often than necessary: ​​this accelerates the wear of the cylinder in the block;

- piston grooves for rings: if the width of the grooves is more than permissible, then both pistons and rings must be replaced;

- piston skirt (part of the outer cylindrical surface of the piston, located below the axis of the piston pin):

- during operation, the surface of the skirt is erased, located in a plane perpendicular to the axis of the piston pin

— it is necessary to replace the piston;

- the hole of the piston pin in the piston is broken along the axis of the piston: if the gap is large, replace the piston;

- bushing in the upper head of the connecting rod: if worn, replace the bushing;

- piston pin: the point of contact with the connecting rod head and the point of contact with the piston bosses wear out. It should fit snugly (with interference) into the upper head of the connecting rod.

In case of wear, when replacing pistons, connecting rods, upper connecting rod bushings - replace the piston pins;

- during operation, the connecting rods experience either compression or tension, so they, as a rule, lose their shape (bend, twist), do not straighten such connecting rods - change them immediately. The dimensions of the connecting rods are shown in table 1.

Size groups according to piston diameter

Label

Piston diameter, mm

A

79,475±0,005

B

79,485±0,005

C

79,495±0,005

- rarely, but it happens that the connecting rod breaks or stretches the lower head (on the connecting rod journal of the crankshaft) - change damaged connecting rods.

The piston pin must match the diameter of both the upper head of the connecting rod and the hole for the piston pin.

The piston diameter must match the diameter of the cylinder in the block.

When assembled, the connecting rod + piston + piston rings units should not differ in mass by cylinders, the difference is not more than 6 g. Otherwise, the engine will not work evenly enough, which eventually leads to fatigue failure of parts.

Разборка, проверка шатунно-поршневой группы двигателя К4М

Piston diameter measurement should be done according to figure 2.

The piston diameter is measured at a distance X=42.00±0.01 mm from the piston head.

The overall height of the piston is 55 mm.

Dimensional groups of pistons in table 1.

The piston pin is pressed into the upper head of the connecting rod and sits loosely in the piston bosses.

Piston pin size:

Length, mm: - 61.7 - 62.0;

Outer diameter, mm: - 19.986 - 19.991;

Internal diameter, mm: - 11.6 no more.

Разборка, проверка шатунно-поршневой группы двигателя К4М

The location of the piston rings is shown in Figure 3.

Piston ring sizes are shown in table 2.

 

thickness, mm

gap in the lock, mm

Top compression ring 1

1,470-1,490

0,15-0,30

lower compression ring 2

1,470-1,495

0,40-0,60

Oil ring expander 3

1,470-1,530

0,20-0,90

Oil ring disc 4

0,420-0,449

0,20-0,90

The wear of the ring around the perimeter is difficult to measure, so the gap in the lock of the ring is measured.

This gap ensures that the ring expands normally when it is heated along with the engine, so it is by no means zero on a cold engine.

When the ring is worn around the perimeter, this gap increases, which is checked by measurement.

Разборка, проверка шатунно-поршневой группы двигателя К4М

Install the piston ring (1) in the cylinder (see fig. 4).

Push the piston ring (1) to the middle of the cylinder with the piston (2) upside down.

Measure the ring gap in the lock with a set of feeler gauges (3).

Replace the piston rings if the gaps are out of tolerance. If the gaps remain out of tolerance and with new rings (see Table 2), replace the cylinder block.

Checking the piston ring clearance in the piston grooves

Thoroughly clean both the rings and the grooves of the pistons from resins, otherwise the measurement will be inaccurate.

Разборка, проверка шатунно-поршневой группы двигателя К4М

Use a feeler gauge to check the clearances between the piston grooves and the piston rings (see Fig. 5).

The gap for the upper compression ring should be in the range of 0.04-0.08 mm.

The gap for the lower compression ring should be in the range of 0.025-0.07 mm.

The clearance for the oil scraper ring should be in the range of 0.08-0.22 mm.

At an output of sizes of backlashes for the specified limits replace piston rings or the piston with a piston finger and rings.