3208 INDUSTRIAL ENGINE ATTACHMENTS – Crankshaft Main Bearings

Remove & Install Crankshaft Main Bearings

Start By:

a. remove oil pan

1. Check each main bearing cap for its location on the engine. Each cap has a number which gives the location of that cap. Make a note that the number on each cap is toward the front of the cylinder block.

2. Remove the bolts and washers that hold main bearing cap (2) in place. Remove the bearing cap and the lower half of the main bearing. Use Tool (C) to remove the bolts that hold the No. 1 main bearing cap in position.

3. Remove bearing (1) from the bearing cap.

4. Turn the crankshaft until Tool (A) can be installed in the oil hole in the crankshaft journal. Install Tool (A). Turn the crankshaft in the direction which will push the upper main bearing out, tab end first.

NOTE: The number one main bearing journal has no oil hole. To remove this bearing, put a thin piece of soft material, that will not damage the crankshaft journal, against the end of the bearing opposite the tab. Hit the bearing with the soft material until the tab of the bearing is free from the groove in the block.


If the crankshaft is turned in the wrong direction, the tab of the bearing will be pushed between the crankshaft and the cylinder block. This will cause damage to the crankshaft and block.

NOTE: Install the bearings dry when the clearance checks are made. Put clean engine oil on the bearings for final assembly.

5. Install the lower bearing in the bearing caps. Install upper bearings (bearing with the oil hole) in the cylinder block with Tool (A).


When bearing caps are installed, make sure the number on the side of the cap is next to and respective with the number on the engine block.

If the serviceman wants to measure the bearing clearances, Plastigage is recommended. Lead wire, shim stock or use of a dial bore gauge can damage the bearing surface.

The serviceman must be very careful to use Plastigage correctly. The following points must be remembered.

… Make sure that the backs of the bearings and the bores are clean and dry.

… Make sure that the bearing locking tabs are properly seated in their slots.

… The crankshaft must be free of oil where the Plastigage touches it.

… If the main bearing clearances are checked with the engine upright or on its side, the crankshaft must be supported. Use a jack under an adjacent crankshaft counterweight, and hold the crankshaft against the crown of the bearing. If the crankshaft is not supported, the weight of the crankshaft will cause incorrect readings.

… Put a piece of Plastigage on the crown of the bearing half that is in the cap. Do notallow the Plastigage to extend over the edge of the bearing.

… Install the bearing cap using the correct torque-turn specifications. Do notuse an impact wrench. Be careful not to dislodge the bearing when the cap is installed.

Do notturn the crankshaft with the Plastigage installed.

… Carefully remove the cap but do notremove the Plastigage. Measure the width of the Plastigage while it is in the bearing cap or on the crankshaft journal. Do this by using the correct scale on the package. Record the measurements.

… Remove the Plastigage before reinstalling the cap.

When using Plastigage, the readings can sometimes be unclear. For example, all parts of the Plastigage are not the same width. Measure the major widths to make sure that they are within the specification range. Also, experience has shown that when checking clearances tighter than 0.10 mm (.004 in)the readings may be low by 0.013 to 0.025 mm (.0005 to .0010 in). Out-of-round journals can give faulty readings. Also, journal taper may be indicated when one end of the Plastigage is wider than the other.

For complete details concerning measuring bearing clearances, see Engine Bearings & Crankshafts, SEBD0531.

6. Check the bearing clearance with Tool (B) as follows:

a. Put cap (3) in position and install the bolts.

b. Tighten bolt (5) to a torque of 40 ± 4 N·m (30 ± 3 lb ft).

c. Tighten bolt (4) to a torque of 40 ± 4 N·m (30 ± 3 lb ft).

d. Put a mark on both bolt heads and the bearing cap.

e. Tighten bolt (5) 120 ± 5 degrees(1/3 turn) more.

f. Tighten bolt (4) 120 ± 5 degrees(1/3 turn) more.

7. Remove the bearing cap, and measure the thickness of the Plastigage. The main bearing clearance must be 0.076 to 0.168 mm (.0030 to .0066 in). The maximum permissible clearance is 0.18 mm (.007 in).

8. Put Clean Engine Oilon the bolt threads and washer faces. Put clean engine oil on the lower half of the main bearing. Put the bearing cap and lower half of the main bearing in position on the engine. Install the bolts. Tighten bolt (5) to a torque of 40 ± 4 N·m (30 ± 3 lb ft). Tighten bolt (4) to a torque of 40 ± 4 N·m (30 ± 3 lb ft). Put a mark on both heads and the cap. Tighten bolt (4) 120 ± 5 degrees(1/3 turn) more. Tighten bolt (5) 120 ± 5 degrees(1/3 turn) more.

9. Do Steps 1 through 8 for the remainder of the bearings.

10. Check the crankshaft end play with Tooling (D). The end play is controlled by the thrust bearing on No. 4 main bearing. The end play with new bearings must be 0.08 to 0.25 mm (.003 to .010 in). The maximum permissible end play with used bearings is 0.36 mm (.014 in).

End By:

a. install oil pan