Crankshaft Main Bearing

MAIN BEARING CAPS

- The main bearing cap bolts (1) must be tightened in the proper sequence. First the inner main cap bolts, secondly the windage tray bolts, lastly the main cap tie (horizontal) bolts.
- Install the inside main bearing cap bolts and tighten to 20 Nm + 1/4 turn (15 ft. lbs. + 1/4 turn).
- Measure crankshaft end play. Procedures
- Install connecting rods and measure side clearance. Service and Repair
- Install windage tray. Lubricate bolts with engine oil. Finger tighten all bolts first, then tighten to 28 Nm + 90° turn (20 ft. lbs. + 90° turn) beginning with the inside bolts tightening outward.
- Install the main cap tie (horizontal) bolts and tighten to 28 Nm (250 in. lbs.).







STANDARD PROCEDURE - CRANKSHAFT MAIN BEARING FITTING





The main bearings use a "select fit" system to achieve proper oil clearances between the bearings and the crankshaft. When main bearings are being selected for a new crankshaft, the block and crankshaft grade identification marks must be used to identify the correct main bearings to use.





The cylinder block main bearing bore grade codes (1) are located on the left side front of the engine block, just below the cylinder head mounting surface. These grade marks (1, 2, 3, or 4) are read left to right, corresponding to main bearing bore 1, 2, 3, or 4.

The grade marks for the crankshaft are located on the rearmost crankshaft counter weight. The crankshaft journal grade marks (A, B, or C) are read left to right, corresponding with journal number 1, 2, 3, 4. For an example, if the main bore grade on the side of the engine block is 3 and the journal grade on the #9 counterweight of the crankshaft is B, the proper select fit bearing would be a (2) +0.003 mm (+0.0001 in.).

Refer to the EXAMPLE CRANKSHAFT MAIN BEARING SELECTION DATA for a more detailed example of how to properly select the main bearings.

NOTE: Service main bearings have a number from (1-5) marked in ink on the bearing surface. For verification, refer to the MAIN BEARING SELECTION CHART for number to size identification.





The upper main bearing (2) has an oil feed hole and a center groove to allow lubrication of the main journal and must be properly positioned in the block.





How to Determine Crankshaft Main Bearing Class





This example shows how to determine the bearing class needed for each crankshaft main journal, assuming that a new crankshaft is being installed in a new or existing engine block. If the code 'B' 'B' 'A' 'C' is stamped on the #9 counterweight of the crankshaft (3), and the code '1' '2' '2' '3' is stamped on the side of the engine block (1), then main #1 would require Class 4 bearings, main #2 would require Class 3 bearings, main #3 would require Class 2 bearings, and main #4 would require Class 3 bearings.