Selecting a piston for a cylinder (VAZ-2121)

Calculated clearance between piston and cylinder (for new parts) is 0.06-0.08 mm (since 1988 the gap has been reduced to 0.05-0.07 mm). It is determined by measuring the cylinders and pistons and is ensured by installing pistons of the same class as the cylinders. Maximum allowable clearance (when parts wear out) — 0.15 mm.

Note: The piston diameter is measured in a plane perpendicular to the piston pin, at a distance of 52.4 mm from the piston bottom (see fig. 2-25).

According to the outer diameter, pistons are divided into five classes (A, B, C, D, E) through 0.01 mm, and by the diameter of the hole for the piston pin - into three categories through 0.004 mm. The piston class (letter) and the category of the hole for the piston pin (number) are stamped on the piston bottom.

If the clearance of a previously used engine exceeds 0.15 mm, then it is necessary to re-select the pistons to the cylinders so that the clearance is as close as possible to the calculated one.

Spare parts are supplied in classes A, C, E. These classes are sufficient to select a piston for any cylinder, since pistons and cylinders are divided into classes with some overlapping sizes.

The article is copied from the website [VAZBOOK.ru]