Connecting rod and piston group (VAZ-2121)

Contents: Piston ↓ Piston pin ↓ Connecting rod ↓

Piston

The diameter of pistons of different classes, measured perpendicular to the axis of the pin at a distance of 55 mm from the piston bottom, mm.

class A - 81.965-81.975
class B - 81.975-81.985
class C - 81.985-81.995
class D - 81,995-82,005
class E - 82.005-82.015

The piston weight is strictly maintained during manufacturing. Therefore, there is no need to select pistons by weight when assembling the engine.

Fig. 9-1 shows the piston markings. Markings 2 in the form of a square or triangle refer to repair pistons. The triangle corresponds to an increase in diameter of 0.4 mm, and the square - to 0.8 mm.

Fig. 9-1. 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

Arrow 1 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

The piston pin is a hollow steel, floating type, i.e. it rotates freely in the piston bosses and connecting rod bushing. The pin is fixed in the piston by two steel retaining rings.

Connecting rod

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 with a 0.004 mm increment (the same as pistons). Class 5 number is stamped on the upper head of the connecting rod.

(The article is taken from an online resource VAZbook.ru)

By the weight of the upper and lower heads, connecting rods are divided into classes (Table 9-1), 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 32.5 mm (Fig. 9-2).

Fig. 9-2. Areas where metal removal is permitted when adjusting the weight of the upper and lower connecting rod heads

Before assembling the connecting rod and piston group, select the pin for the piston and connecting rod. For new parts, the class of holes for the pin in the connecting rod and piston must be identical to the class of the pin. For used parts, the selection of the pin for the piston and connecting rod is identical to that described in Section II (see chapter "Pistons and connecting rods").