Device Features
The main dimensions of the cylinder block are given in fig. 2-30.
Pic. 2-30. The main dimensions of the cylinder block.
The cylinder block is cast from special low-alloy cast iron. Cylinder diameters are divided into five classes through 0.01 mm, denoted by the letters A, B, C, D, E. The cylinder class is stamped on the lower plane of the cylinder block (pic. 2-31).
Pic. 2-31. Cylinder size marking on the block.
It is possible to bore cylinders for repair pistons, increased in diameter by 0.4 and 0.8 mm.
The main bearing caps are machined complete with the cylinder block. Therefore, they are not interchangeable and have risks on the outer surface to distinguish (see fig. 2-19).
Checking the technical condition and repair
Examination. Wash the cylinder block thoroughly and clean the oil passages. After blowing and drying with compressed air, inspect the cylinder block. Cracks in bearings or other places in the cylinder block are not allowed.
If there is a suspicion that coolant has entered the crankcase, then check the tightness of the cylinder block on a special stand. To do this, after plugging the holes in the cooling jacket of the cylinder block, inject water at room temperature into it at a pressure of 0.3 MPa (3 kgf/cm2). Within two minutes, there should be no leakage of water from the cylinder block.
If oil gets into the coolant, then without completely disassembling the engine, check for cracks in the cylinder block in the areas of the oil channels. To do this, drain the coolant from the cooling system, remove the cylinder head, fill the cooling jacket of the cylinder block with water and supply compressed air to the vertical oil channel of the cylinder block. If air bubbles appear in the water filling the cooling jacket, replace the cylinder block.
Check the split plane of the cylinder block with the head using a ruler and a set of feeler gauges. The ruler is installed along the diagonals of the plane and in the middle in the longitudinal direction and across. The flatness tolerance should not exceed 0.1 mm.
Cylinder repair. Check if the wear of the cylinders exceeds the maximum allowable - 0.15 mm.
Cylinder diameter is measured with a bore gauge (pic. 2-32) in four zones, both in the longitudinal and transverse direction of the engine (pic. 2-33). A micrometer is used to set the caliper to zero.
Pic. 2-32. Measuring cylinders with a bore gauge:
Pic. 2-33. Cylinder measurement scheme:
A and B - directions of measurements;
1, 2, 3 and 4 - belt numbers.
In the belt zone 1, the cylinders practically do not wear out. Therefore, by the difference in measurements in the first and other zones, one can judge the amount of cylinder wear.
If the maximum wear is more than 0.15 mm, bore the cylinders to the nearest repair size, leaving an allowance of 0.03 mm for the honing diameter. Then honing the cylinders, maintaining such a diameter that when installing the selected repair piston, the estimated clearance between it and the cylinder was 0.025-0.045 mm.