Measurement of Main Dimensions of 1. Imported Bearings

1. Inner diameter of imported bearing: before measurement, the bearing shall be assembled according to regulations and the bearing cap bolts shall be tightened according to the specified torque. With an inner diameter gauge, the reference size shall be measured after the outer diameter micrometer is calibrated, and the thinning area shall be avoided during measurement. The difference between the inner diameter of the imported bearing and the outer diameter of the corresponding journal is the fit clearance.

2. Imported bearing thickness: The fixed probe of the outer diameter micrometer is changed from a plane to a spherical surface, which can be used to measure the thickness of the imported bearing. The thickness of the imported bearing should generally be controlled within the range of 0.005-0.010mm, otherwise the inner diameter of the imported bearing will be out of tolerance. The imported bearing has a slight thinning near the opening, which should be paid attention to during measurement.

3. The matching tightness between the imported bearing and the bearing hole: The matching tightness is guaranteed by the free bounce amount and the height of the remaining surface of the imported bearing. The method of measuring the height of the remaining surface is as follows: assemble the bearing according to the regulations, tighten the bearing cover bolts to the specified torque, loosen one of the bolts, and measure the clearance at the bearing cover interface with a feeler gauge. The value should be within the range of 0.05-0.15mm.

4. Coaxiality of the inner hole of the main bearing: The coaxiality error of the inner hole of the main bearing is mainly caused by the coaxiality error of the bearing hole, and the cause of the coaxiality error of the bearing hole is the deformation of the cylinder body. When the radial runout of the main journal is within the specified tolerance, check the seal marks of the main journal and the bearing. If the position of the seal marks of each main bearing is obviously inconsistent, it means that the coaxiality error is large, and it can be scraped and bored. The bearing or replacement of the cylinder block is solved, otherwise it is difficult to ensure the normal operation of the engine.

Measurement of bearing clearance for imported 2.

Imported bearing clearance refers to the amount of movement when the bearing is not installed on the shaft or bearing box, the inner or outer ring of the bearing is fixed, and then the unfixed side is moved radially or axially. According to the moving direction, it can be divided into radial clearance and axial clearance. The internal clearance of the installed forward bearing is generally expressed by the theoretical clearance. From the theoretical clearance minus the bearing installed on the shaft or housing due to interference fit when the amount of expansion or contraction of the ring clearance is called "installation clearance". The clearance after adding or subtracting the dimensional change caused by the temperature difference inside the bearing is called "effective clearance". The imported bearing is installed with the clearance when the machine is placed under a certain load, that is, the effective clearance plus the elastic deformation generated by the bearing load, so as to be called "working clearance".

When measuring the clearance of imported bearings, in order to obtain a stable measurement value, the specified measurement load is generally applied to the imported bearings. Therefore, the measured value is larger than the real play (called theoretical play), that is, the amount of elastic deformation caused by the measurement load is increased. When the working clearance is slightly negative, the fatigue life of the bearing is very long, but the fatigue life decreases significantly with the increase of the negative clearance. Therefore, when choosing the clearance of imported bearings, it is generally appropriate to make the working clearance zero or slightly positive. In addition, when the rigidity of imported bearings needs to be improved or the noise needs to be reduced, the working clearance should be further negative, while when the temperature rise of imported bearings is severe, the working clearance should be further positive, etc. In addition, specific analysis must be made according to the use conditions.

Measurement of 3. inlet bearing bore

The measurement of the bearing hole of the imported bearing can use the inner diameter gauge to check the reference size on the outer diameter micrometer. At the same time, the roundness and cylindricity of the bearing hole need to be measured. Burned bearings often make the diameter of the bearing hole at the opening shrink and the roundness is out of tolerance, which is extremely unfavorable to the normal operation of the bearing. If the matching of the positioning surface of the connecting rod bolt is loose, the connecting rod bearing cap will shift to make the roundness of the bearing hole out of tolerance. The roundness error of the imported bearing hole should be controlled within the dimensional tolerance, while the cylindricity should be strictly controlled.