Pre-clean all cavities and channels. Use a brush and scraper to remove dirt. The cylinders made in the cylinder block are divided into size classes during production; the required piston clearance is automatically set by using the prescribed pistons. In addition to the nominal diameter, the cylinders can be ground to three size classes, which differ for different engines.
Fig. 81. Measuring the piston diameter at a distance of 42 mm from the bottom
Engines with high mileage have worn cylinders. In this case, new pistons must be used to obtain the required clearance between the cylinder and piston. To accurately measure the clearance, you will need a dial indicator and a micrometer. Measure the inner diameter of the cylinders (in several places) with a dial indicator and the outer diameter of the pistons with a micrometer, as described in the previous subsection (see Fig. 81).
The piston repair sizes are specified in the appendix. The bores for the crankshaft main bearings can be of the nominal size or bored to a larger repair size.
All engines are fitted with fixed size main bearing shells. They are marked with paint.
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