When there is an appropriate oil film on the surface of the bearing, it can absorb the heavy load and shock from the rotating parts in the combustion stroke. This oil film prevents seizing and reduces output loss due to friction. There is an oil hole and oil groove in the upper half-bearing and it supplies oil to the bearing and main journal and lubricates. There is a locking lip to keep the bearing from rotating. The thrust washer absorbs the force applied to the crankshaft in the axial direction. There is an oil groove on the surface that touches the crankshaft. There is a tab on the bottom side thrust washer to keep it from turning. There are some engines that do not have the bottom side thrust washer.
1. Bearing size
There are several standard sizes for crankshaft bearings. This size code is inscribed on the back of the bearing. Use this code when selecting bearings to improve the crankshaft main journal oil clearance precision in order to prevent abnormal noise and seizing and to maintain good fuel economy. As the size code increases, the bearing thickness increases in micron units. Number of standard sizes and size coding differ according to the engine models.
2. Undersize bearing
When the crankshaft main journal is damaged or the oil clearance becomes larger, the main journal is ground and a thicker undersize bearing can be used. There are some engines that cannot accept an undersize bearing replacement. If this is the case, the crankshaft must be replaced.