Crankshaft Main Bearing: Testing and Inspection

CLEARANCE
Use Method A or Method B. Method A is preferred because it is more accurate.

Method A: Using Bore Gauge And Micrometer





1. Set main bearings in their proper positions on cylinder block and main bearing cap.
2. Install main bearing cap to cylinder block and torque to specifications all the bolts in correct order in two or three stages. Service and Repair





3. Measure inner diameter "A" of each main bearing.





4. Measure outer diameter "Dm" of each crankshaft main journal.
5. Calculate main bearing clearance. Main bearing clearance = A - Dm. The standard value is 0.020 - 0.047 mm (0.0008 - 0.0019 inch). The limit is 0.1 mm (0.004 inch). If it exceeds the limit, replace the bearing.

^ If clearance cannot be adjusted within the standard of any bearing, grind crankshaft journal and use undersized bearing.





^ When grinding the crankshaft journal, confirm that dimension "L" (fillet roll) is more than the specified limit. "L" is 0.1 mm (0.004 inch).
^ If crankshaft or cylinder block is replaced, select thickness of main bearings as follows:





a. The grade number of each cylinder block main journal is punched on the respective cylinder block. These numbers are punched in either Arabic or Roman numerals.





b. The grade number of each crankshaft main journal is punched on the respective crankshaft. These numbers are punched in either Arabic or Roman numerals.





c. Select main bearing with suitable thickness according to the table shown. For example:
Main journal grade number: 1
Crankshaft journal grade number: 2
Main bearing grade number = 1 + 2 = 3

Method B: Using Plastigage

If incorrect bearing clearance exists, use a thicker or undersized main bearing to ensure the specified clearance.

NOTE: Do not turn crankshaft or connecting rod while plastigage is being inserted.