2.9.1. Features of the device

Fig. 2.31. Main sizes of a rod

Fig. 2.32. Sizes of piston rings
Fig. 2.33. Main sizes of the piston

The main sizes of conrod and piston group are given in fig. 2.31,2.32, 2.33.
The piston — aluminum cast. On outer diameter pistons are broken into five classes (And, B, C, D, E) through 0,01 mm. The external surface of the piston has irregular shape. Therefore it is necessary to measure diameter of the piston only in the plane, perpendicular to a piston finger, at distance of 55 mm from the piston bottom.

Fig. 2.34. Marking of the piston: 1 – an arrow for orientation of the piston in the cylinder; 2 – repair size; 3 – piston class; 4 – an opening class for a piston finger

On diameter of an opening under a piston finger pistons are subdivided into three classes (1, 2, 3) through 0,004 mm. Classes of diameters of the piston and an opening under a piston finger are branded on the bottom of the piston (fig. 2.34).
Pistons are sorted by weight on three groups: normal, increased and reduced by 5 g. To these groups there corresponds marking on the piston bottom: "", "+" and "–". On the engine all pistons have to be one group on weight.
Pistons of the repair sizes are manufactured with the outer diameter increased by 0,4 and 0,8 mm. To increase by 0,4 mm there corresponds marking in the form of a triangle, and to increase by 0,8 mm — in the form of a square.
The arrow on the bottom of the piston shows how it is correct to focus the piston at its installation in the cylinder. It has to be directed towards the camshaft drive.
The piston finger — steel hollow, floating type, freely rotates in lugs of the piston and the plug of a rod. In a piston opening the finger is fixed by two lock rings. On outer diameter fingers are subdivided into three classes through 0,004 mm. The class is marked by paint at a finger end face: a blue tag — the first, green — the second, and red — the third class.
Piston rings are made of cast iron. The top compression ring — with the chromeplated barrel-shaped external surface. Lower compression ring of scraper type. An oil scraper ring — with the chromeplated working edges and with a razzhimny twisted spring.
On rings of the repair sizes digital marking "40" or "80" is put that corresponds to increase in outer diameter by 0,4 or 0,8 mm.

Fig. 2.35. Marking of a rod: 1 – a rod class on weight and on an opening in the top head; 2 – number of the cylinder

Rod — steel, shod. The rod is processed together with a cover and therefore they are separately not interchanged. That at assembly not to mix covers and rods, on them number 2 (fig. 2.35) of the cylinder in which they are established is branded.
In the top head of a rod the stalebronzovy plug is pressed. On diameter of an opening of this plug rods are subdivided into three classes through 0,004 mm. Number of a class 1 is branded on a rod cover.
On the mass of the top and lower heads rods are subdivided into the classes marked by either a letter, or paint on a rod cover. On the engine rods of one class on weight have to be established.

Fig. 2.36. Places on which it is allowed to delete metal, at adjustment of mass of the top and lower heads of a rod

It is possible to adjust the mass of rods removal of metal from lugs on the top head and on a cover to the minimum sizes 33 and 32 of mm (fig. 2.36). After removal of metal from a rod cover on it it is necessary to brand rod classes on an opening under a piston finger and on weight.

Table 2.1   Classes of rods on the mass of the top and lower heads
Mass of heads of a rod,
Color of marking
489+3 495+3 501+3
Red Green
489+3 495+3 501+3
489+3 495+3 501+3