The settlement gap between the piston and the cylinder (for new details) makes 0,05–0,07 mm. It is defined by a measurement of cylinders and pistons and is provided with installation of pistons of the same class, as cylinders. The most admissible gap (at wear of details) — 0,15 mm.

Fig. 3-25. Main sizes of the piston, rod, piston finger and piston rings

NOTE Diameter of the piston is measured in the plane, perpendicular to a piston finger, at distance of 52,4 mm from the piston bottom (see fig. 3-25). On outer diameter pistons are broken into five classes (A, B, C, D, E) through 0,01 mm, and on diameter of an opening under a piston finger — on 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

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If at the engine which was in operation, the gap exceeds 0,15 mm, then it is necessary to pick up anew pistons to cylinders that the gap was perhaps closer to settlement.

In spare parts pistons of the classes A, C, E are delivered. These classes are enough for selection of the piston to any cylinder as pistons and cylinders are broken into classes with some overlapping of the sizes.