GM 6.5L V8 – Crankshaft Support

The cylinder case has five split bores to support the crankshaft (see Figure 2-4). Four bolts retain each bearing cap to the cylinder case. Each bore uses a two-piece sleeve bearing insert providing an oil clearance for the crankshaft. The #3 bore has a bearing insert with thrust flanges to control crankshaft end-play.
During engine manufacture, a combination of three bearing insert sizes is used at each of the five bores and is based on crankshaft journal measurements (refer to Figure 2-5). Upper insert halves have an oil groove, and lower insert halves have no groove.

The crankshaft installation procedure requires the following steps:
• Seat all main bearing caps with a mallet and initially tighten both the inner and outer bolts for each main bearing cap.
• Thrust the crankshaft rearward and forward, using a mallet.
• Insert a soft wedge between the crankshaft and a bearing cap to keep the crankshaft in its forward position.
• Tighten the two inner bolts for each main bearing cap to 104-118 Nm (141 -160 lb-ft) torque.
• Tighten the two outer bolts for each main bearing cap to 126-145 Nm (93-107 Ib-ft) torque.

For service purposes, bearing size combinations provide the following oil clearance, as measured with the plastigage procedure:
• Bearing #1, #2, #3 and #4: 0.045 to 0.083 mm (0.0018 to 0.0033 in.)
• Bearing #5: 0.055 to 0.093 mm (0.0022 to 0.0037 in.)

Three sizes of main bearing inserts are available for service:
• Standard
• 0.013 mm (0.0005 in.) U.S. (Undersize)
• 0.026 mm (0.001 in.) U.S. (Undersize)

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