Piston - aluminum casting. During manufacturing, the piston weight is strictly maintained. Therefore, when assembling the engine, it is not necessary to select pistons of the same group by weight.
According to the outer diameter, pistons are divided into five classes (A, B, C, D, E) through 0.01 mm. The outer surface of the piston has a complex shape. It is conical in height and oval in cross-section. Therefore, it is necessary to measure the piston diameter only in the plane perpendicular to the piston pin, at a distance of 55 mm from the piston bottom.
According to the diameter of the hole for the piston pin, pistons are divided into three classes (1, 2, 3) through 0.004 mm. The classes of piston diameters and holes for the piston pin are stamped on the piston bottom (Fig. 2-30).
Fig. 2-30. Piston and connecting rod markings:
1 - arrow for orienting the piston in the cylinder; 2 - repair size; 3 - piston class; 4 - piston pin bore class; 5 - class of connecting rod by piston pin bore; 6 - cylinder number.
Pistons of repair sizes are manufactured with an outer diameter increased by 0.4 and 0.8 mm. The bottoms of these pistons are marked with a triangle or square. The triangle corresponds to an increase in the outer diameter by 0.4 mm, and the square - by 0.8 mm.
The arrow on the piston bottom shows how to correctly orient the piston when installing it in the cylinder. It should be directed towards the camshaft drive.
Piston pin - steel, hollow, floating type, i.e. freely rotates in the piston bosses and connecting rod bushing. The pin is fixed in the piston by two steel retaining rings.
According to the outer diameter, the pins are divided into three classes, each with a 0.004 mm interval. The class is marked with paint on the end of the pin: blue mark - first, green - second, and red - third class.
Piston rings - made of cast iron. Upper compression ring - with chrome-plated barrel-shaped outer surface. Lower compression ring of scraper type. Oil scraper ring - with chrome-plated working edges and with expansion coil spring (expander).
On rings of repair sizes, the digital marking "40" or "80" is placed, which corresponds to an increase in the outer diameter by 0.4 or 0.8 mm.
Connecting rod - steel, forged. It is processed together with the cover, and therefore they are not interchangeable separately. In order not to mix up the covers and connecting rods during assembly, they are stamped with number 6 (Fig. 2-30) of the cylinder in which they are installed. During assembly, the numbers on the connecting rod and cover must be on the same side.
A steel-bronze bushing is pressed into the upper head of the connecting rod. According to the diameter of the hole in this bushing, the connecting rods are divided into three classes, each 0.004 mm (the same as pistons). Class 5 number is stamped on the upper head of the connecting rod.
By the weight of the upper and lower heads, connecting rods are divided into classes (Table 2-1), marked with paint on the connecting rod rod. Connecting rods of the same weight class must be installed on the engine. The weight of the connecting rods can be adjusted by removing metal from the bosses on the heads to the minimum dimensions of 16.5 and 35.5 mm (Fig. 2-31).
Table 2-1. Connecting rod classes by weight of upper and lower heads
