|
4-8-4-shatunno-porshnevaya-gruppa.html
4.8.4. Conrod and piston group
Piston of the engine of fashion. 2106
|
|
1, 2 and 3 – the planes of measurement of a profile of a skirt;
4 – the exaggerated skirt profile in longitudinal section (perpendicular to an axis of a piston finger) |
The piston and the cylinder corresponding to it have to belong to one class as well as the piston with a piston finger to one category.
Prevention
On outer diameter pistons are broken into five classes (And, B, C, D, E), and on diameter of an opening under a piston finger – into three categories through 0,004 mm. A piston class (letter) and category of an opening under a piston finger (figure) are branded on the piston bottom.
The sizes of diameter of a skirt in mm
|
A
|
78,930 – 78,940
|
|
B
|
78,940 – 78,950
|
|
With
|
78,950 – 78,960
|
|
D
|
78,960 – 78,970
|
|
E
|
78,970 – 78,980
|
For selection of the piston to any cylinder pistons and cylinders are broken into classes with some overlapping of the sizes. Therefore in spare parts pistons only of classes A, C, E are delivered. These classes are enough for selection of pistons to any cylinder
The main thing at selection of the piston – to provide a necessary assembly gap between the piston and the cylinder which is defined by a measurement of the cylinder and piston.
The difference of bigger and smaller diameters of a skirt of the piston in cross section makes 0,4 mm.
At selection of new pistons to the worn-out cylinder the gap between a skirt of the piston and a mirror of a sleeve should be checked in the lower, least worn-out part of the cylinder. It is impossible to allow reduction of a gap in this part of the cylinder to value less than 0,02 mm.
At assembly of the engine it is necessary to pay attention to tags on
pistons: the letter P or an arrow showing the correct position of the piston in the cylinder have to be turned to a forward part of the engine.
At maintenance, as a rule, install pistons of the same size in partially worn-out cylinders (normal or repair) what the pistons working earlier in this engine had. However it is desirable to pick up a set of pistons with a big diameter of a skirt for reduction of a gap between the piston and a mirror of the cylinder.
Pistons change most often owing to wear of a flute of the top piston ring less often because of wear of a skirt of the piston.
It is expedient to replace pistons in the same terms, as piston rings.
In spare parts pistons deliver both nominal, and the repair sizes, with the increased diameter of a skirt.
Numbers of repair pistons and size of increase in diameter of a skirt
|
Number of the piston
|
Increase in diameter
|
|
21011-1004015-21
|
0,4 mm
|
|
21011-1004015-22
|
0,4 mm
|
On repair pistons of the engine of fashion. 2106 on the bottom the largest diameter of a skirt of the piston rounded to 0,01 mm and its weight are beaten out.
|
|
