Main Bearing-Fitting
MAIN BEARINGS
Fig. 15
Bearing caps are not interchangeable and should be marked at removal to insure correct assembly (Fig. 15). Upper and lower bearing halves are NOT interchangeable. Lower main bearing halves of 1, 3 and 4 are interchangeable. Upper main bearing halves of 1, 3 and 4 are interchangeable.
CRANKSHAFT MAIN JOURNALS
Fig. 14
Measure the journal outside diameter as shown in (Fig. 14). Refer to Engine; Specifications.
The crankshaft journals should be checked for excessive wear, taper and scoring. (Fig. 14) Limits of taper or out-of-round on any crankshaft journals should be held to 0.025 mm (0.001 inch). Journal grinding should not exceed 0.305 mm (0.012 inch) under the standard journal diameter. Do NOT grind thrust faces of Number 2 main bearing. Do NOT nick crank pin or bearing fillets. After grinding, remove rough edges from crankshaft oil holes and clean out all passages.
CAUTION: With the nodular cast iron crankshafts used it is important that the final paper or cloth polish after any journal regrind be in the same direction as normal rotation in the engine.
Fig. 16
Upper and lower Number 2 bearing halves are flanged to carry the crankshaft thrust loads and are NOT interchangeable with any other bearing halves in the engine (Fig. 16). All bearing cap bolts removed during service procedures are to be cleaned and oiled before installation. Bearing shells are available in standard and the following undersizes: 0.025 mm (0.001 inch) and 0.254 mm (0.010 inch). Never install an undersize bearing that will reduce clearance below specifications.
CRANKSHAFT OIL CLEARANCE
Engine crankshaft bearing clearances can be determined by use of Plastigage or the equivalent. The following is the recommended procedures for the use of Plastigage with the engine in the vehicle or engine on a repair stand.
PLASTIGAGE METHOD-ENGINE IN-VEHICLE
NOTE: The total clearance of the main bearings can only be determined with the engine in the vehicle by removing the weight of the crankshaft. This can be accomplished by either of two following methods:
1. Preferred method:
a. Shim the bearings adjacent to the bearing to be checked in order to remove the clearance between upper bearing shell and the crankshaft. This can be accomplished by placing a minimum of 0.254 mm (0.010 inch) shim (e. g. cardboard, matchbook cover, etc.) between the bearing shell and the bearing cap on the adjacent bearings and tightening bolts to 14 - 20 Nm (10 - 15 ft. lbs.).
b. When checking #1 main bearing shim #2 main bearing.
c. When checking #2 main bearing shim #1 & #3 main bearing.
d. When checking #3 main bearing shim #2 & #4 main bearing.
e. When checking #4 main bearing shim #3 main bearing
NOTE: Remove all shims before reassembling engine.
2. Alternative Method:
a. Support the weight of the crankshaft with a jack under the counterweight adjacent to the bearing being checked.
3. Remove oil film from surface to be checked. Plastigage is soluble in oil.
Fig. 17
4. Place a piece of Plastigage across the entire width of the bearing shell in the cap approximately 6.35 mm (1/4 inch) off center and away from the oil holes (Fig. 17). (In addition, suspected areas can be checked by placing the Plastigage in the suspected area). Torque the bearing cap bolts of the bearing being checked to the proper specifications.
Fig. 18
5. Remove the bearing cap and compare the width of the flattened Plastigage (Fig. 18) with the metric scale provided on the package. Locate the band closest to the same width. This band shows the amount of clearance in thousandths of a millimeter. Differences in readings between the ends indicate the amount of taper present. Record all readings taken. Refer to Engine; Specifications. Plastigage generally is accompanied by two scales. One scale is in inches, the other is a metric scale.
NOTE: Plastigage is available in a variety of clearance ranges. Use the most appropriate range for the specifications you are checking.
PLASTIGAGE METHOD-ENGINE OUT-OF-VEHICLE
1. With engine in the inverted position (crankshaft up) and mounted on a repair stand, remove main journal cap.
2. Remove oil from journal and bearing shell.
3. Cut Plastigage to same length as width of the bearing and place it in parallel with the journal axis (Fig. 17).
4. Carefully install the main bearing cap and tighten the bolts to specified torque.
CAUTION: Do not rotate crankshaft or the Plastigage will be smeared.
Fig. 19
5. Carefully remove the bearing cap and measure the width of the Plastigage at the widest part using the scale on the Plastigage package (Fig. 19). Refer to Engine; Specifications for proper clearances. If the clearance exceeds the specified limits, replace the main bearing(s) with the appropriate size, and if necessary, have the crankshaft machined to next undersize.
CAUTION: Do not rotate crankshaft or the Plastigage may be smeared.