(1) Measurement of bearing hole
For the measurement of the bearing hole, the inner diameter gauge can be used to check the reference size on the outer diameter micrometer, and the roundness and cylindricity of the bearing hole shall also be measured. Burning out the bearing often reduces the diameter of the bearing hole at the opening and the roundness is out of tolerance,
which is extremely unfavorable to the normal operation of the bearing. If the locating surface of the connecting rod bolt fits loosely, the connecting rod bearing cap will shift and the roundness of the bearing hole will exceed the tolerance. The roundness error of bearing hole shall be controlled within the dimensional tolerance, while the cylindricity shall be strictly controlled.
(2) Measurement of main dimensions of bearing
① Bearing thickness: fix the outside micrometer and change the measuring head from plane to Bore Dimensions spherical surface, which can be used to measure the bearing thickness.
The bearing thickness shall generally be controlled within the range of 0.005 ~ 0.010 mm, otherwise the Bore Dimensions inner diameter of the bearing will exceed the tolerance. The bearing has slight thinning near the opening, which should be paid attention to during measurement.
② Fit tightness of bearing and bearing hole: the fit tightness is guaranteed by the free spring opening of bearing and the height of surplus surface. Under Bore Dimensions the method of measuring the height of the remaining surface:
assemble the bearing according to the regulations, tighten the bolts of the bearing cover to the specified torque, loosen one of the bolts, and measure the clearance at the interface of the bearing cover with a feeler gauge, Bore Dimensions which shall be within the range of 0.05 ~ 0.15mm.
③ Bearing inner diameter: before measurement, the bearing shall be installed according to the regulations and the bearing cover bolts shall be tightened according to the specified torque. The inner diameter gauge Bore Dimensions shall be used to measure after the reference dimension is measured with the outer diameter micrometer.
The thinning area shall be avoided during measurement. The difference between the bearing inner diameter Bore Dimensions and the corresponding journal outer diameter is the fit clearance.
④ Coaxiality of the inner hole of the main bearing: the coaxiality error of the inner hole of the main bearing is Bore Dimensions mainly caused by the coaxiality error of the bearing hole, and the coaxiality error of the bearing hole is caused by the deformation of the cylinder block.
When the radial circular runout of the main journal is within the specified tolerance, check the bite marks of the main journal and the bearing. If the bite marks of each main bearing are obviously inconsistent, it indicates that the coaxiality error is large, which can be solved by scraping, boring the bearing or replacing the cylinder block, otherwise it is difficult to ensure the normal operation of the engine.
Different from small bearings, super large bearings are processed by single machine, single person and single piece, with strong randomness, which is very easy to cause out of tolerance of dimension or shape, such as small grinding amount after machining, out of tolerance of heat treatment deformation, excessive shrinkage and uneven shrinkage, carburizing pad damage, handling collision and jamming, etc.
If processed according to the normal process, these parts will become nonconforming products. After Bore Dimensions analysis, some nonconforming products can be saved by taking measures.