Piston
Pistons 4 and 6 (Fig. 3) of all engine models are cast from aluminum alloy. The outer surface of the piston is coated with a thin layer of tin to improve its running-in to the cylinder walls. To compensate for uneven thermal expansion, the piston skirt 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 a plane perpendicular to the piston pin and at a distance of 52.4 mm from the piston bottom.
By the outer diameter of the pistons (same as the cylinder) are divided into five classes through 0.01 mm, and according to the diameter of the hole under the piston pin 5 - into three categories 0.004 mm (see table 1). Piston class (latin letter) and the category (number) are marked on the piston bottom.
Spare parts are supplied in piston classes A, C, E, which are quite sufficient for selecting a piston for any cylinder, since pistons and cylinders are divided into classes with some overlap in size.
The hole for the piston pin is offset from the axis of symmetry by 1.5 mm to the right side of the engine. Therefore, there is a mark 11 on the piston in the form of the letter P for the correct orientation of the piston in the cylinder. The mark, as well as the hole 10 on the connecting rod for the oil outlet, should be facing the front of the engine.
Since 1986, pistons of repair sizes for all engine models have been manufactured with an outer diameter increased by 0.4 and 0.8 mm. Before 1986, pistons of the following repair sizes were produced: for the 2105 engine with an increase of 0.4; 0.7 and 1.00 mm, and for engines 2101 and 2103 with an increase of 0.2; 0.4 and 0.6 mm.
Pistons of different engine models are easy to distinguish from each other by their appearance. Pistons 4 for 2105 engines have two recesses for valves in the bottom. Pistons for 2101 and 2103 engines are the same, with a smooth bottom without recesses.
Piston rings
The piston has two compression rings 2 and 3 and one oil scraper ring 1. All of them are made of cast iron. The upper compression ring has a barrel-shaped chromed outer surface. The lower compression ring is a scraper type, phosphated.
Piston pin
All engine models are equipped with the same steel tubular piston pins 5 (see fig. 3). They are pressed into the upper head of the connecting rod 7 and rotate freely in the piston bosses. According to the outer diameter, the pins are divided into three categories through 0.004 mm. The pin category is marked on its end with the corresponding color: 1st - blue, 2nd - green and 3rd - red.
Connecting rod
Steel, forged, identical for all engine models. The lower head of the connecting rod is split, connecting rod liners 9 are installed in it. The connecting rod is machined together with the cover 8, and therefore they are not interchangeable with the covers of other connecting rods. In order not to mix up the connecting rod covers during assembly, the connecting rod and its cover (on the side) have a stamp of the cylinder number in which they are installed. During assembly, the numbers on the connecting rod and cover must be on the same side.