GM Full-Size Trucks 1980-1987 Repair Guide

Main Bearing

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REPLACEMENT



See Figures 1 and 2

Engine Out of Car
  1. Remove and inspect the crankshaft.
  2.  
  3. Remove the main bearings from the bearing saddles in the cylinder block and main bearing caps.
  4.  
  5. Coat the bearing surfaces of the new, correct size main bearings with clean engine oil and install them in the bearing saddles in the block and in the main bearing caps.
  6.  
  7. Install the crankshaft. See Crankshaft Installation.
  8.  



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Fig. Fig. 1: Remove the bearing cap from the main bearing that needs to be replaced



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Fig. Fig. 2: Remove the bearing from the cap

Engine in Car

See Figures 3 and 4

  1. With the oil pan, oil pump and spark plugs removed, remove the cap from the main bearing needing replacement and remove the bearing from the cap.
  2.  



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Fig. Fig. 3: Home-made bearing roll-out pin



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Fig. Fig. 4: With the bearing roll-out pin installed, rotate the crankshaft clockwise to push the upper bearing from the block

  1. Make a bearing roll-out pin, using a bent cotter pin as shown in the illustration. Install the end of the pin in the oil hole in the crankshaft journal.
  2.  
  3. Rotate the crankshaft clockwise as viewed from the front of the engine. This will roll the upper bearing out of the block.
  4.  
  5. Lube the new upper bearing with clean engine oil and insert the plain (un-notched) end between the crankshaft and the indented or notched side of the block. Roll the bearing into place, making sure that the oil holes are aligned. Remove the roll pin from the oil hole.
  6.  
  7. Lube the new lower bearing and install the main bearing cap. Install the main bearing cap, making sure it is positioned in proper direction with the matchmarks in alignment.
  8.  
  9. Torque the main bearing cap bolts to specification.
  10.  

See Crankshaft Installation for thrust bearing alignment.

CRANKSHAFT END PLAY AND INSTALLATION



See Figure 5

When main bearing clearance has been checked, bearings examined and/or replaced, the crankshaft can be installed. Thoroughly clean the upper and lower bearing surfaces, and lube them with clean engine oil. Install the crankshaft and main bearing caps.

Dip all main bearing cap bolts in clean oil, and torque all main bearing caps, excluding the thrust bearing cap, to specifications (see the Crankshaft and Connecting Rod chart in this Section to determine which bearing is the thrust bearing). Tighten the thrust bearing, pry the crankshaft the extent of its axial travel several times, holding the last movement toward the front of the engine. Add thrust washers if required for proper alignment. Torque the thrust bearing cap to specifications.

To check crankshaft end-play, pry the crankshaft to the extreme rear of its axial travel, then to the extreme front of its travel. Using a feeler gauge, measure the end-play at the front of the rear main bearing. End-play may also be measured at the thrust bearing. Install a new rear main bearing oil seal in the cylinder block and main bearing cap. Continue to reassemble the engine.



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Fig. Fig. 5: Measuring crankshaft end-play at the front of the rear main bearing

 
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