- clearance between cylinder and piston of nominal diameter exceeds 0.07 mm;
- ovality (difference of diameters of one level) exceeds 0.04 mm;
- taper (diameter difference in the upper and lower sections) exceeds 0.05 mm.
Pistons should be replaced if there is mechanical or thermal damage (melting or burning, cracks, etc.); if the wear of the piston grooves has exceeded the permissible values (see below); if the wear of the piston skirt exceeds 0.04 mm, Since the wear of all pistons is approximately the same, it is advisable in case of mechanical and thermal damage to replace the damaged piston, and in other cases - to replace the entire set of pistons, The dimensions of the repair pistons are given in the Table of Dimensional and Installation Data (table 3).
The required cylinder size for boring is determined by measuring the diameter of the new oversized piston, as shown in fig. 72, that is, at a distance of 10 mm above the lower edge of the piston skirt, perpendicular to the axis of the piston pin hole. From the sum of the piston diameter and 0.03 mm gap, subtract 0.02 mm for cylinder honing.
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