Measuring the inner diameter of a cylinder

Check if the wear of the cylinders exceeds the maximum allowable - 0.08 mm. Why measure the inner diameter of the cylinder with a special measuring device - a caliper in three zones - in the upper, middle and lower parts of the cylinder (pic. 60) both transverse and longitudinal directions of the engine.

When measuring the upper and lower zones of the cylinder, one should retreat 10 mm from their edges. Thus, when measuring the inner diameter of a cylinder, it is necessary to take six measurements for each cylinder.

All obtained values should be recorded and compared with the values given in the table of adjustments and control. If the maximum wear of at least one of the cylinders is more than 0.08 mm, bore all the cylinders to the nearest repair size.

To determine the amount of cylinder bore, measure the piston diameter, add another 0.03 mm to the obtained value, due to the runout of the piston during its stroke, and, in addition, add 0.02 mm for the final honing of the cylinder.




The piston has a complex shape of the outer surface. Therefore, the piston diameter is measured with a micrometer at a distance of 6 mm from the edge of the piston skirt and at right angles to the piston pin holes (pic. 61).

The difference between the measured piston diameter and its nominal value should not exceed 0.04 mm, otherwise it is necessary to install a piston with an increased diameter - repair size. For the VR6 engine, oversized pistons are manufactured with a diameter increased by 0.5 and 1.0 mm.

To check the runout of the piston during its stroke, measure the piston diameter and the inner diameter of the cylinder. Calculate the difference between the values obtained for each cylinder. If the difference is more than 0.08 mm, then the cylinders should be bored out, since the runout has reached the wear limit.