2.2.22. Check of cylinders, pistons and piston rings

Check cylinder walls for existence of scratches, roughnesses or crests that indicates excessive wear. If cylinder walls uneven or have deep scratches, the cylinder demands boring to the repair size and installation of pistons of the increased diameter.

Fig. 2.137. The scheme of measurement and measurement of diameter of the cylinder in the longitudinal and cross direction of the engine: a – 50 mm; b – 95 mm

Using a nutromer 1, measure diameter of the cylinder in the longitudinal and cross direction of the engine in two provisions ("a" and "b"), as shown in the figure 2.137.

In the presence of any of the following conditions chisel the cylinder.

Diameter of the cylinder exceeds extreme value.

The difference of diameters in two provisions (see above) exceeds the admission of conicity.

The difference of diameters in the longitudinal and cross direction of the engine exceeds the admission of ovality.

Nominal rate: 78,000–78,014 mm.

Extreme value: 78,114 mm.

Admission of conicity and ovality: 0,10 mm.

NOTE In need of boring of any of four cylinders, at repair of the engine all four cylinders have to be chiseled to the same following repair size. It is necessary for uniformity and balance.

Check the piston for existence of damages and cracks. The damaged or defective piston has to be replaced.

Fig. 2.138. Measurement of diameter of the piston

As shown in the figure 2.138, diameter of the piston has to be measured in situation "a" from the end of a skirt of the piston in the direction, perpendicular to a piston finger.

Standard size: 77,953–77,968 mm.

The standard size (new (with a covering)): 77,969–77,984 mm.

The increased size of 0,50 mm: 78,453–78,468 mm.

Measure diameter of the cylinder and diameter of the piston, a difference of the specified sizes represents gap size between the piston and the cylinder. The gap between the piston and the cylinder has to be within norm. If the gap differs from norm, chisel the cylinder and use the piston of the increased repair size.

Fig. 2.139. Measurement of a gap between the piston and the cylinder

Nominal rate: 0,032–0,061 mm.

Nominal rate (the piston with a covering (new)): 0,016–0,045 mm.

Extreme value: 0,161 mm.

NOTE In this case diameter of the cylinder is measured in the axial direction of the engine in two provisions.

Check is made at piston flutes, pure, dry and free from a deposit.

Establish a new piston ring 1 in a piston flute and measure a gap by the probe 2.

Fig. 2.140. Measurement of a gap between a piston ring and a flute: and – 19,5 mm

If the gap – differs from norm, replace the piston.

To measure a gap in the lock of a piston ring, install a piston ring 1 in the cylinder, and then measure a gap by the probe 2. If the measured gap differs from norm, replace a ring.

Fig. 2.141. Measurement of a gap in the lock of a piston ring: and – 120 mm

NOTE Remove a deposit and clear the top part of the cylinder before installation of a piston ring.