The oil clearance for the crankshaft bearing and the connecting rod bearing is determined by the engine model. Each bearing should be selected to obtain the proper oil clearance with regard to the cylinder block main journal bore size and crankshaft main journal diameter, or the connecting rod big end bore size and crank pin diameter. As the bore size increases or the journal or pin diameter decreases, the thickness of the bearing to be used increases.
Oil clearance
Oil clearance is the gap between the bearing and the shaft. Oil covers the parts so that metal parts do not make direct contact with other metal parts. When the oil clearance becomes larger, abnormal sounds occur and oil pressure decreases, leading to seizing.
Bearing selection method
Use the following process to determine the correct bearing (size code).
A+B=C
ACylinder block main journal bore size code (or connecting rod big end bore size code)
BCrankshaft main journal size code (or crank pin size code)
CTotal number
Example:
ACylinder block main journal bore size code4
BCrankshaft main journal size code3
CA+B=4+3=7
Select the bearing with a size code of 3 from the chart on the left. In this case, the total number is used as is for the bearing size code from the chart. The selecting method varies by the engine model. And there are some engines where the total number becomes as it is for the bearing size code. There are some engine models that do not have a rank for the crankshaft main journal or crank pin. In this case, select a bearing with the same size code as the cylinder block main journal bore size code or connecting rod big end bore size code.