GM Lumina/Grand Prix/Cutlass Supreme/Regal 1988-1996

Crankshaft and Main Bearings

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REMOVAL & INSTALLATION



See Figure 1

Click image to see an enlarged view

Fig. Fig. 1: Exploded view of the crankshaft and main bearings-1996 vehicle shown

  1. Disconnect the negative battery cable.
  2.  
  3. Remove the engine assembly as outlined earlier in this section.
  4.  
  5. Remove the engine front timing cover, then remove the timing chain and sprockets.
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  7. Remove the oil pan as outlined earlier in this section.
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  9. Remove the oil pump. On the 2.5L engine, remove the force balancer assembly.
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  11. Stamp the cylinder number on the machined surfaces of the bolt bosses of the connecting rods and caps, if not done by the factory, for identification when installing. If the pistons are to be removed from the connecting rod, mark the cylinder number on each piston with an indelible marker, silver pencil or quick drying paint for proper cylinder identification and cap to rod location.
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  13. Remove the connecting rod caps and store them so that they can be installed in their original positions. Put pieces of rubber fuel hose on the rod bolts before removal to protect the connecting rod journals.
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  15. Mark and remove all the main bearing caps.
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  17. Note the position of the keyway in the crankshaft so it can be installed in the same position.
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  19. With an assistant, lift the crankshaft out of the block. The rods will pivot to the center of the engine when the crankshaft is removed.
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  21. Remove the rear main oil seal.
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To install:
  1. Measure the crankshaft journals with Plastigage®to determine the correct size rod and main bearings to be used. Whenever a new or reconditioned crankshaft is installed, new connecting rod bearings and main bearings must be installed. The bearing undersize are usually 0.010 in. (0.254mm), 0.020 in. (0.501mm) and 0.030 in. (0.762mm). Do not go any further undersize than 0.030 in. (0.762mm).
  2.  
  3. Clean all oil passages in the block (and crankshaft if it is being reused).
  4.  

A new rear main seal should be installed any time the crankshaft is removed or replaced.

  1. Install sufficient oil pan bolts in the block to align with the connecting rod bolts. Use rubber bands between the bolts to position the connecting rods as required. Connecting rod position can be adjusted by increasing the tension on the rubber bands with additional turns around the pan bolts or thread protectors. Install, if not already done, pieces of rubber hose on the connecting rod bolts to protect the crankshaft journals during installation.
  2.  
  3. Position the upper half of main bearings in the block and lubricate them with assembly lube. Position crankshaft keyway in the same position as removed. With an assistant, lower the crankshaft into the block. The connecting rods will follow the crank pins into the correct position as the crankshaft is lowered.
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  5. Lubricate the thrust flanges with Assembly Lube 10501609 or equivalent. Install rod caps with the lower half of the bearings lubricated with assembly lube. Lubricate the cap bolts with assembly lube and install, but do not tighten.
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  7. With a block of wood, bump the crankshaft in each direction to align the thrust flanges of the main bearing. After bumping the shaft in each direction, wedge the shaft to the front and hold it while tightening the thrust bearing cap bolts.
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In order to prevent the possibility of cylinder block and/or main bearing cap damage, the main bearing caps are to be tapped into their cylinder block cavity using a wood or rubber mallet before the bolts are installed. Do not use attaching bolts to pull the main bearing caps into their seats. Failure to observe this information may damage the cylinder block or a bearing cap.

  1. Tighten all main bearing caps to the figures listed in the torque specifications chart in this section.
  2.  
  3. Remove the connecting rod bolt thread protectors and lubricate the connecting rod bearings with suitable assembly lube.
  4.  
  5. Install the connecting rod bearing caps in their original position. Tighten the nuts to the figures listed in the torque specifications chart in this section.
  6.  
  7. Install the oil pump, oil pan, timing cover, accessories and install the engine assembly into the vehicle as outlined earlier in this section.
  8.  
  9. Connect the negative battery cable.
  10.  

CLEANING AND INSPECTION



See Figures 2, 3 and 4

  1. Clean the crankshaft with solvent and brush. Clean the oil passages with a suitable brush, then blow them out using compressed air.
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Click image to see an enlarged view

Fig. Fig. 2: Checking the crankshaft for excessive runout



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Fig. Fig. 3: Checking the main bearing journal using a micrometer



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Fig. Fig. 4: Checking the main bearing bore diameter with the bearings installed

  1. Inspect the crankshaft for obvious damage or wear. Check the main and connecting rod journals for cracks, scratches, grooves or scores. Inspect the crankshaft oil seal surface for nicks, sharp edges or burrs that could damage the oil seal or cause premature wear.
  2.  
  3. If the crankshaft passes a visual inspection, check journal runout using a dial indicator. Support the crankshaft in V-blocks as shown in the figure and check the runout as shown. Compare to specifications.
  4.  
  5. Measure the main and connecting rod journals for wear, out-of-roundness or taper, using a micrometer. Measure in at least four places around each journal and compare your findings with the journal diameter specifications.
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  7. If the crankshaft fails any inspection for wear or damage, it must be reground or replaced.
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MAIN BEARING REPLACEMENT



See Figures 5 and 6

The following procedure requires the use of Plastigage®or a micrometer set consisting of inside and outside micrometers, and a dial indicator.

  1. Inspect the bearings for scoring, chipping or other wear.
  2.  
  3. Inspect the crankshaft journals as details in the Cleaning and Inspection procedure
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  5. If the crankshaft journals appear usable, clean them and the bearing shells until they are completely free of oil. Blow any oil from the oil hole in the crankshaft.
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Click image to see an enlarged view

Fig. Fig. 5: Apply a strip of gauging material to the bearing, then install the cap



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Fig. Fig. 6: Remove the cap and compare the gauging material to the provided scale

  1. To check the crankshaft/rod bearing clearances using a micrometer, use the perform the following procedures:
    1. Set the crankshaft on V-blocks Using a dial indicator set on the center bearing journal, check the crankshaft runout. Repair or replace the crankshaft if out of specification.
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    3. Using an outside micrometer, measure the crankshaft bearing journals for diameter and and out-of-round conditions; if necessary, regrind the bearing journals.
    4.  
    5. Install the bearings and caps, then tightening the nuts/bolts to specifications. Using an inside micrometer, check the bearing bores in the engine block. If out of specification, regrind the bearing bores to the next largest oversize.
    6.  
    7. The difference between the two readings is the bearing clearance. If out of specification, inspect for the cause and repair as necessary.
    8.  

  2.  
  3. To inspect the main bearing surfaces using the Plastigage®method, perform the following procedures:
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The journal surfaces and bearing shells must be completely free of oil to get an accurate reading with Plastigage®

  1. Place a strip of Plastigage®or equivalent gauging material, lengthwise along the bottom center of the lower bearing shell, then install the cap with the shell and tightening the connecting rod nuts or main cap bolt to specification.
  2.  

When the Plastigage®material is installed on the bearing surfaces, DO NOT rotate the crankshaft.

  1. Remove the bearing cap with the shell. The flattened Plastigage®will either be sticking to the bearing shell or the crankshaft journal.
  2.  
  3. Using the printed scale on the Plastigage®package, measure the flattened material at its widest point. the number on the scale that most closely corresponds to the width of the Plastigage®indicates the bearing clearance in thousandths of an inch or hundredths of a millimeter.
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  5. Compare your findings with the bearing clearance specification. If the bearing clearance is excessive. the bearing must be replaced or the crankshaft must be ground and the bearing replaced.
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Bearing shell sets over the standard size are available to correct excessive bearing clearance.

  1. After clearance measurement is completed, be sure to remove the Plastigage®from the crankshaft and/or bearing shell.
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  3. For final bearing shell installation, make sure the connecting rod and rod cap and/or cylinder block and main cap bearing saddles are clean and free of nicks or burrs. Install the bearing shells in the bearing saddles, making sure the shell tangs are seated in the notches.
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Be careful when handling any plain bearings. Your hands and the working area should be clean. Dirt is easily embedded in the bearing surface and the bearings are easily scratched or damaged.

 
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