GM Astro/Safari 1985-1996 Repair Guide

Crankshaft and Main Bearings

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REMOVAL & INSTALLATION



See Figures 1, 2, 3, 4 and 5



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Fig. Fig. 1: Place hose over the connecting rod studs to protect the crankshaft and cylinders from damage



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Fig. Fig. 2: Support the connecting rods with rubber bands and install rubber rod bolt caps to protect the crankshaft during removal and installation



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Fig. Fig. 3: Plastigage® or an equivalent gauging material should be used to check main bearing clearances



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Fig. Fig. 4: You can use a feeler gauge to check the crankshaft end-play during installation



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Fig. Fig. 5: Align the thrust bearing (as illustrated), then tighten the main bearing caps to specification

  1. Drain the crankcase oil and remove the engine from the van.
  2.  
  3. Remove the flywheel/flexplate and mount the engine on a work stand in a suitable working area. Invert the engine, so the oil pan is facing up.
  4.  

If the cylinder heads are not being removed, the spark plugs should be removed in order to release engine compression and allow for easier rotation of the crankshaft when necessary.

  1. Remove the engine front (timing) cover.
  2.  
  3. Align the timing marks, then remove the timing chain (on the 4.3L engine) and gears.
  4.  

After removing the timing gear or sprocket from the crankshaft, be sure to remove the woodruff key from the crankshaft.

  1. Remove the oil pan.
  2.  


CAUTION
The EPA warns that prolonged contact with used engine oil may cause a number of skin disorders, including cancer! You should make every effort to minimize your exposure to used engine oil. Protective gloves should be worn when changing the oil. Wash your hands and any other exposed skin areas as soon as possible after exposure to used engine oil. Soap and water, or waterless hand cleaner should be used.

  1. If necessary, remove the oil pump assembly.
  2.  
  3. Inspect the connecting rods and bearing caps for identification marks (numbers). If there are none, stamp the cylinder number on the machined surfaces of the bolt bosses of the connecting rods and caps for identification when reinstalling. If the pistons are to be removed eventually from the connecting rod, mark the cylinder number on the pistons with silver paint or felt-tip pen for proper cylinder identification and cap-to-rod location.
  4.  
  5. Remove the connecting rod nuts and caps, then store them in the order of removal. Place short pieces of rubber hose on the connecting rod studs to prevent damaging the crankshaft bearing surfaces.
  6.  
  7. Check the main bearing caps for identification marks (if not identified, mark them). Remove the main bearing caps and store them in order, for reassembly purposes; the caps must be reinstalled in their original position.
  8.  
  9. If equipped, remove the 1-piece rear main seal retainer from the engine.
  10.  
  11. Install rubber bands between a bolt on each connecting rod and oil pan bolts that have been reinstalled in the block (see illustration). This will keep the rods from banging on the block when the crank is removed.
  12.  
  13. Carefully lift the crankshaft out of the block. The rods will pivot to the center of the engine when the crank is removed.
  14.  

When removing the bearing shells, it is recommended to replace them with new ones.

  1. Using solvent, clean all of the parts for inspection purposes. If necessary, replace any part that may be questionable.
  2.  

To install:
  1. Install new bearing shell inserts and check the bearing clearances. For details, please refer to the crankshaft cleaning and inspection information found later in this section.
  2.  

If necessary, deliver the crankshaft to an automotive machine shop, have the crankshaft journals ground and new bearing shells matched.

  1. Lubricate all of the parts and oil seals with clean engine oil.
  2.  
  3. Using a feeler gauge and a medium prybar, move the crankshaft forward-and-rearward. Check the crankshaft end-play by inserting a feeler gauge between the crankshaft and the thrust bearing shell. An alternate method is to use a dial indicator at the crankshaft snout. Install the indicator, move the crankshaft rearward, zero the indicator and then move the crankshaft forward. The dial indicator will read the end-play.
  4.  
  5. Tighten main bearing caps (in three steps) to specification:

    2.5L engine (1985-88): 70 ft. lbs. (95 Nm)
     
    2.5L engine (1989-90): 65 ft. lbs. (88 Nm)
     
    4.3L engine (1985): 70 ft. lbs. (95 Nm)
     
    4.3L engine (1986): 75 ft. lbs. (100 Nm)
     
    4.3L engine (1987-90): 80 ft. lbs. (108 Nm)
     
    4.3L engine (1991-95): 75 ft. lbs. (95 Nm)
     
    4.3L engine (1996): 77 ft. lbs. (105 Nm)
     

  6.  
  7. Remove the rubber hoses from the studs. Install the bearing cap (with bearing shell) onto the connecting rod and the cap nuts. Tighten the connecting rod cap nuts to specification.

    2.5L engine (1985-88): 32 ft. lbs. (43 Nm)
     
    2.5L engine (1989-90): 30 ft. lbs. (40 Nm)
     
    4.3L engine (1985-90): 45 ft. lbs. (61 Nm)
     
    4.3L engine (1991-92): 20 ft. lbs. (27 Nm) + a 60° turn
     
    4.3L engine (1993-96): 20 ft. lbs. (27 Nm) + a 70° turn
     

  8.  

When there is more than one connecting rod/piston assembly being installed, the connecting rod cap nuts should only be tightened enough to keep each rod in position until all have been installed. This will ease the installation of the remaining piston assemblies.

  1. Check the clearance between the sides of the connecting rods and the crankshaft using a feeler gauge. Spread the rods slightly with a small prybar to insert the feeler gauge. If the clearance is below the minimum tolerance, the rod may be machined to provide adequate clearance. If the clearance is excessive, substitute an unworn rod and recheck. If clearance is still outside specifications, the crankshaft must be welded and reground or replaced.
  2.  
  3. If necessary, install the pump assembly.
  4.  
  5. Install the oil pan.
  6.  
  7. Make sure the woodruff key is installed in the end of the crankshaft, then install the timing chain (4.3L only) and gears.
  8.  
  9. Install the engine front (timing) cover.
  10.  
  11. Remove the engine from the work stand, then install the flywheel/flexplate.
  12.  
  13. Refill the crankcase and install the engine to the van.
  14.  

CLEANING & INSPECTION



See Figures 3, 6, 7, 8, 9 and 10



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Fig. Fig. 6: A dial gauge may be used to check crankshaft end-play



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Fig. Fig. 7: Carefully pry the shaft back and forth while reading the dial gauge for play



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Fig. Fig. 8: A dial gauge may also be used to check crankshaft run-out



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Fig. Fig. 9: Mounting a dial gauge to read crankshaft run-out



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Fig. Fig. 10: Turn the crankshaft slowly by hand while checking the gauge

  1. Clean the crankshaft with solvent and a brush. Clean the oil passages with a suitable brush, then blow them out with compressed air.
  2.  
  3. 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 seal wear.
  4.  
  5. If the crankshaft passes a visual inspection, check journal runout using a dial indicator. Support the crankshaft in V-blocks (or in the bearings on the engine block as shown if V-blocks are not available) and check the shaft runout. If crankshaft runout exceeds 0.001 in. (0.025mm) the shaft should be replaced. Consult a machine shop for advice.
  6.  
  7. Measure the main and connecting rod journals for wear, out-of-roundness or taper, using a micrometer. Measure in at least 4 places around each journal and compare your findings with the journal diameter specifications.
  8.  
  9. If the crankshaft fails any inspection for wear or damage, it must be reground or replaced.
  10.  

The crankshaft used on the 2.5L engine is of the rolled fillet type and cannot be reground. If the measurements do not meet specification, replace the shaft.

  1. Once the crankshaft has been cleared for a return to service, check the bearings using Plastigage® or an equivalent gauging material. The bearings must be checked regardless of whether they are new or used. To check the bearings:
    1. Temporarily install the upper and lower bearing halves to the block and main bearing cap (respectively).
    2.  
    3. Wipe all oil from the crankshaft journal and outer/inner surfaces of the bearing shell.
    4.  
    5. Temporarily position the crankshaft to the block and upper bearing journals.
    6.  
    7. Place a piece of Plastigage® material in the center of the bearing.
    8.  
    9. Install the bearing cap and bearing. Lubricate the main bearing bolts with engine oil, install the bolts and tighten them to specifications.
    10.  
    11. Remove the bearing cap and determine the bearing clearance by comparing the width of the flattened Plastigage® material at its widest point with the graduations on the gaging material container. The number within the graduation on the envelope indicates the clearance in millimeters or thousandths of an inch. If the clearance is greater than allowed, REPLACE BOTH BEARING SHELLS AS A SET. Recheck the clearance after replacing the shells.
    12.  

  2.  

MAIN BEARING REPLACEMENT



See Figures 3 and 11



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Fig. Fig. 11: A roll-out pin can be fabricated from a cotter pin and used to replace bearings with the crankshaft installed

Main bearing clearances must be corrected by the use of selective upper and lower shells. under NO circumstances should the use of shims behind the shells to compensate for wear be attempted. The bearings are easily replaced if the crankshaft is removed from the engine, but provided that no refinishing or replacement of the crankshaft is necessary, the bearings can also be replaced with the engine and crankshaft still installed in the van. To replace the main bearing shells, proceed as follows:

  1. Refer to the Oil Pan, Removal and Installation procedures in this section and remove the oil pan.
  2.  
  3. If necessary, remove the oil pump assembly.
  4.  
  5. Loosen all of the main bearing cap bolts.
  6.  
  7. Remove the bearing cap bolts, the caps and the lower bearing shell.
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  9. Insert a flattened cotter pin or a roll out pin in the oil passage hole in the crankshaft, then rotate the crankshaft in the direction opposite to the cranking rotation. The pin will contact the outside edge of the upper shell and roll it out.
  10.  
  11. The main bearing journals should be checked for roughness and wear. Slight roughness may be removed with a fine grit polishing cloth, saturated with engine oil. Burrs may be removed with a fine oil stone. If the journals are scored or ridged, the crankshaft must be replaced.
  12.  

The journals can be measured for out-of-round with the crankshaft installed by using a crankshaft caliper and inside micrometer or a main bearing micrometer. The upper bearing shell must be removed when measuring the crankshaft journals. Maximum out-of-round of the crankshaft journal must not exceed 0.0010 in. (0.025mm).

  1. Clean the crankshaft journals and bearing caps thoroughly before installing the new main bearings.
  2.  
  3. Place the new upper shell on the crankshaft journal with the locating tang in the correct position and rotate the shaft to turn it into place using a cotter pin or a roll out pin as during removal.
  4.  
  5. Place a new bearing shell in the bearing cap.
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  7. Check the main bearing clearances using a gauging material. In order to do this you will have to support the crankshaft (at the flywheel and damper) to be certain that all clearance is taken-up between the upper bearing half and the shaft journal. Then apply a strip of gauging material to each of the bearings, install and tighten all of the main bearing caps, then remove the caps again and check the gauging material. For more details, please refer to the crankshaft cleaning and inspection information, found earlier in this section.
  8.  
  9. Lubricate the new bearings and the main bearing cap bolts with engine oil, then install the main bearing caps and tighten to specification.
  10.  
  11. Using a feeler gauge, pry the crankshaft forward and rearward, then check for the crankshaft (thrust bearing) end-play.
  12.  

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 brass or leather mallet before the bolts are installed. Do not use the bolts to pull the main bearing caps into their seats. Failure to observe this procedure may damage the cylinder block or bearing cap.

  1. Install the oil pump assembly.
  2.  
  3. Install the oil pan.
  4.  

 
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