Crankshaft & Main Bearings

Before disassembly, ensure main bearing caps are numbered for location, and arrow on cap points toward timing chain end of crankshaft. Remove main bearing caps and bolts, along with lower bearing halves.
Cylinder block main bearing bore size is indicated by letter "A", "B", or "C" stamped on lower crankcase. See Fig 2. Ensure main bearing bore is within specification. See MAIN BEARING BORE SPECIFICATIONS table.
Crankshaft main bearing journal sizes are indicated by numbers stamped crankshaft. See Fig 3. Ensure main bearing journal is within specification. See MAIN BEARING JOURNAL DIAMETER SPECIFICATIONS table.

Fig 1: Positioning Piston Rings
Courtesy of GENERAL MOTORS CORP.

Fig 2: Locating Cylinder Block Main Bearing Bore Codes
Courtesy of GENERAL MOTORS CORP.

Fig 3: Locating Crankshaft Main Bearing Journal Size Codes
Courtesy of GENERAL MOTORS CORP.

Fig 4: Locating Cylinder Bore Diameter Paint Codes
Courtesy of GENERAL MOTORS CORP.

NOTE: Main bearings are color code marked. Standard bearings have one color code mark. All undersize bearings have 2 color code marks, except undersize bearing with Red only color code mark.
If main bearing journal and main bearing bore are within specification, replace main bearings with new bearings matching original color code mark. If color code on original bearing cannot be determined, use letter stamped on lower crankcase to determine proper bearing size. See MAIN BEARING SELECTION (STANDARD) table. Main bearings are available in undersizes. All undersize bearings have 2 color code marks, except undersize bearing with Red only color code mark. See Fig 5. Undersize bearings are available in 5 thickness variations. See BEARING THICKNESS SPECIFICATIONS table.
If necessary, regrind main journals to .010" (.25 mm) undersize with a 2.2729-2.2736" (57.732-57.750 mm) finished diameter. Using finished journal diameter and letter marked on lower crankcase, determine undersize main bearing color code. See MAIN BEARING SELECTION (UNDERSIZE) table. Measure reground crankshaft journals to ensure out-of-round and taper do not exceed .0004" (.01 mm).

When installing main bearing caps, ensure arrow on cap points toward timing chain end of crankshaft. Tighten 10 main bearing cap bolts and 12 lower crankcase bolts in sequence and to specification. See Fig 6. See TORQUE SPECIFICATIONS .

Fig 5: Identifying Main Bearing Color Codes

Courtesy of GENERAL MOTORS CORP.

Fig 6: Main Bearing Cap Bolt & Lower Crankcase Bolt Tightening Sequence

Courtesy of GENERAL MOTORS CORP.

MAIN BEARING BORE SPECIFICATIONS

Lower Crankcase Letter Code	Diameter - In. (mm)
"A"	2.4409-2.4412 (62.000-62.006)
"B"	2.4412-2.4414 (62.006-62.012)
"C"	2.4414-2.4416 (62.012-62.018)

MAIN BEARING JOURNAL DIAMETER SPECIFICATIONS

Crankshaft Number Code	Diameter - In. (mm)
1	2.2832-2.2834 (57.994-58.000)
2	2.2830-2.2832 (57.988-57.994)
3	2.2828-2.2829 (57.982-57.988)

MAIN BEARING SELECTION (STANDARD)

Lower Crankcase Letter Code	Crankshaft Number Code	Bearing Color Code
"A"	1	Green
"A"	2	Black
"A"	3	No Color
"B"	1	Black
"B"	2	No Color
"B"	3	Yellow
"C"	1	No Color
"C"	2	Yellow
"C"	3	Blue

BEARING THICKNESS SPECIFICATIONS

Bearing Color Code		In. (mm)
Standard Bearings
Green		.0785-.0786 (1.993-1.999)
Black		.0786-.0787 (1.996-2.000)
No Color		.0787-.0788 (1.999-2.003)
Yellow		.0788-.0789 (2.002-2.006)
Blue		.0789-.0790 (2.005-2.009)
Undersize Bearings
Green & Red		.0834-.0835 (2.118-2.122)
Black & Red		.0835-.0836 (2.121-2.125)
Red (Only)		.0836-.0837 (2.124-2.128)
Yellow & Red		.0837-.0838 (2.127-2.131)
Blue & Red		.0838-.0839 (2.130-2.134)

MAIN BEARING SELECTION (UNDERSIZE)

Finished Journal Diameter	Lower Crankcase Letter	Bearing Color Code
2.2729-2.2731 (57.732-57.738)	"A" "B" "C"	Red Yellow & Red Blue & Red
2.2731-2.2733 (57.738-57.744)	"A" "B" "C"	Black & Red Red Yellow & Red
2.2734-2.2736 (57.744-57.750)	"A" "B" "C"	Green & Red Black & Red Red