Crankshaft Main Bearing Fitting

Fig 1: ENGINE BLOCK MAIN BORE GRADE

Courtesy of CHRYSLER LLC

The main bearings are a "select fit" to achieve proper oil clearances. For main bearing selection, the block and crankshaft have grade identification marks.

The marks for the cylinder block main bore grade are located on the right front side of the engine block . These grade marks (1, 2, or 3) are read left to right, corresponding to main bore 1, 2, 3, 4. The 5th digit is a check some digit for plant validation during manufacturing.

Fig 2: CRANKSHAFT MAIN JOURNAL GRADE MARKING LOCATION - REAR OF BLOCK

Courtesy of CHRYSLER LLC

The grade marks for the crankshaft are located on the rearmost crankshaft counter weight as shown in Fig 2 . The crankshaft journal grade marks (A, B, or C) are read left to right, corresponding with journal number 1, 2, 3, 4.

Refer to the MAIN BEARING SELECTION CHART to properly select the main bearings. For an example, if the main bore grade is 3 and the journal grade is B, the proper select fit bearing would be a (2) +0.003 mm (+0.0002 in.).

Fig 3: Main Bearing Grade Marks

Courtesy of CHRYSLER LLC

1 - LOWER MAIN BEARING

2 - UPPER MAIN BEARING

3 - OIL FEED HOLE AND GROOVE

4 - GRADE SELECTION INK MARKS

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 a oil feed hole and a center groove to allow lubrication of the main journal and must be properly positioned in the block.

MAIN BEARING SELECTION CHART

-	-	Main Bearing Bore Grade Marks
-	-	1	2	3
Crankshaft Main Journal Grade Marks Each bearing grade increment of 0.003 mm is for wall thickness so diametrical clearances are adjusted 0.006 mm per select fit class	A	(3) Standard	(2) +003 mm (+0.0001 in.)	(1) +0.006 mm (+0.0002 in.)
	B	(4) -0.003 mm (-0.0001 in.)	(3) Standard	(2) +003 mm (+0.0001 in.)
	C	(5) -0.006 mm (-0.0002 in.)	(4) -0.003 mm (-0.0001 in.)	(3) Standard

CRANKSHAFT DIAMETER - CHART 1

-	Crankshaft Diameter (mm)	-
Min	Max	Grade
63.9870 mm	63.9956 mm	A
63.9957 mm	64.0042 mm	B
64.0043 mm	64.0130 mm	C

BLOCK MAIN BORE DIAMETER - CHART 2

-	Block Main Bore Diameter (mm)	-
Min	Max	Grade
68.9895 mm	68.9964 mm	1
68.9965 mm	69.0034 mm	2
69.0035 mm	69.0105 mm	3

-	-	Block Main Bore Grade
-	-	1	2	3
Crankshaft Journal Grade	A	Class 3	Class 2	Class 1
	B	Class 4	Class 3	Class 2
	C	Class 5	Class 4	Class 3