Piston
Pistons 4 and 6 (pic. 3) 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 adaptability 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 crown.
Outside diameter of pistons (same as cylinder) are subdivided into five classes through 0.01 mm, and according to the diameter of the hole for the piston pin 5 - into three categories of 0.004 mm (see table. 1). Piston class (latin letter) and category (number) marked on the bottom of the piston.
Pistons of classes A, C, E are supplied as spare parts, which are quite enough to select 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, the piston has a mark 11 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, must face towards the front of the engine.
Since 1986, repair size pistons for all engine models have been manufactured with an outer diameter increased by 0.4 and 0.8 mm. Until 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 in appearance. Pistons 4 for engines 2105 have two recesses for valves in the bottom. The pistons for engines 2101 and 2103 are the same, with a smooth bottom without recesses.
Piston rings
The piston has two compression rings 2 and 3 and one oil scraper 1. All of them are made of cast iron. Top compression ring with barrel chrome outer surface. Bottom compression ring scraper type, phosphated.
Piston pin
All engine models use the same tubular steel 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 fingers are divided into three categories through 0.004 mm. The category of the finger is marked on its end with the corresponding color: 1st - blue, 2nd - green and 3rd - red.
Connecting rod
Steel, forged, the same for all engine models. The lower head of the connecting rod is detachable, connecting rod bearings 9 are installed in it. The connecting rod is processed together with the cover 8, and therefore they are not interchangeable with the covers of other connecting rods. In order not to confuse the connecting rod caps during assembly, on the connecting rod and its cap (side) there is a stamp of the number of cylinders in which they are installed. When assembling, the numbers on the connecting rod and cap must be on the same side.