GM Prizm/Nova 1985-1993 Repair Guide

Crankshaft and Main Bearings

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REMOVAL & INSTALLATION



See Figures 1 through 5

  1. Remove the engine assembly from the car, following procedures outlined earlier in this section. Mount the engine securely on a stand which allows it to be rotated.
  2.  
  3. Remove the timing belt and tensioner assemblies.
  4.  
  5. Turn the engine upside down on the stand. Remove the oil pan and the oil strainer.
  6.  
  7. Remove the oil pump.
  8.  
  9. Remove either the clutch and pressure plate (manual transmission).
  10.  
  11. Remove either the flywheel (manual) or the drive plate (automatic).
  12.  
  13. Remove the rear end plate.
  14.  
  15. Remove the rear oil seal retainer.
  16.  
  17. Using a numbered punch set, mark each connecting rod cap with its correct cylinder number. Remove the rod caps and their bearings; keep the bearings with their respective caps.
  18.  
  19. Measure the crankshaft end-play (throughst clearance) before removing the crank. Attach a dial indicator, such as J 8001 or similar, to the end of the block and set the tip to bear on the front end of the crankshaft. With a screw driver, gently move the crankshaft back and forth and record the reading shown on the dial.

    Standard end-play, NEW: 0.02mm
     
    Acceptable end-play: 1985-88 VIN Code 4: 0.020-0.185mm, All others: 0.02-0.22mm
     
    Maximum allowable: 0.3mm
     

  20.  

If the end-play is excessive, the throughst washers will need to be replaced as a set.



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Fig. Fig. 1: Use a dial indicator to measure crankshaft end play

  1. Gradually loosen and remove the main bearing cap bolts in 3 passes and in the correct order. Remove just the bolts, leaving the caps in place.
  2.  



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Fig. Fig. 2: Remove the main bearing cap bolts in this order

  1. When all the bolts are removed, use 2 bolts placed in the No. 3 bearing cap to wiggle the cap back and forth. This will loosen the cap and allow it and the throughst washers to be removed. Note and/or label the throughst washers as to their placement and position. If they are to be reused, they must be reinstalled exactly as they were.
  2.  
  3. Remove the remaining caps. Keep the caps in order and keep the bearing shell with its respective cap.
  4.  



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Fig. Fig. 3: Keep all the pieces in numbered order. Exact reassembly is required

  1. Lift the crankshaft out of the block. The crankshaft is a moderately heavy component.
  2.  
  3. Remove the upper bearing shells from the block and place them in order with the corresponding bearing caps.
  4.  
  5. Check and measure the crankshaft and bearings according to the procedures give in Cleaning and Inspection later in this section.
  6.  
  7. When reassembling, clean the bearing caps and journals in the block thoroughly. Coat the bearings with a liberal application of clean motor oil.
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  9. Fit the upper bearings halves into the block and position the lower bearing halves in the bearing caps.
  10.  
  11. Place the crankshaft into the engine block, making sure it fits exactly into its mounts.
  12.  
  13. Install the upper throughst washers on the center main bearing with the oil grooves facing outward.
  14.  



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Fig. Fig. 4: Correct position of the upper throughst washer when reinstalling

  1. Install the main bearing caps and the lower throughst washers in the proper sequence. Make sure the arrows on the caps point towards the front (pulley end) of the motor.
  2.  
  3. Tighten the cap bolts in 3 passes and in the correct sequence to 44 ft. lbs.
  4.  



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Fig. Fig. 5: Install and tighten the main bearing cap bolts in this order

  1. Double check the end-play of the crank by repeating Step 10 of this procedure.
  2.  
  3. Turn the crankshaft through 1 or 2 full clockwise rotations, making sure that it turns smoothly and evenly with no binding.
  4.  
  5. Attach the piston rods, following procedures given earlier in this section. Remember that the rod caps must be reinstalled in their original positions.
  6.  
  7. Install a new rear main oil seal into the retainer and install the retainer onto the block. Tighten the bolts to 7.0 ft. lbs. (84 inch lbs.).
  8.  
  9. Install the rear end plate on the engine.
  10.  
  11. Install either the driveplate (automatic) or the flywheel (manual), observing the matchmarks made during removal.
  12.  
  13. If equipped with a manual transmission, reinstall the clutch disc and pressure plate.
  14.  
  15. Install the oil pump.
  16.  
  17. Install the oil strainer and oil pan, using new gaskets.
  18.  
  19. Rotate the engine into its upright position and continue reassembly of the timing belt, idler pulley and covers.
  20.  
  21. Reinstall the engine in the car, following procedures outlined earlier in this section.
  22.  

CLEANING AND INSPECTION



See Figures 6, 7, 8, 9 and 10

With the crankshaft removed from the engine, clean the crank, bearings and block areas thoroughly. Visually inspect each crankshaft section for any sign of wear or damage, paying close attention to the main bearing journals. ANY scoring or ridge on the crankshaft means the crankshaft must be replaced. Because of the metallurgy in the crankshaft, welding and/or regrinding the crankshaft is not recommended. The bearing faces of the crank may not be restored to their original condition causing premature bearing wear and possible failure.

Mount the crankshaft on V-blocks and set a dial indicator to bear on the center main journal. Slowly rotate the crank and record the circular runout as shown on the dial. Runout in excess of 0.06mm disqualifies the crankshaft from further use. It must be replaced.



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Fig. Fig. 6: Measuring crankshaft run-out

Using a micrometer, measure the diameter of each journal on the crankshaft and record the measurements. The acceptable specifications for both connecting rod and main journals are found in the Crankshaft and Connecting Rod specifications chart at the beginning of this section. If ANY journal is beyond the acceptable range, the crank must be replaced.

Additionally, each journal must be measured at both outer edges. When one measurement is subtracted from the other, the difference is the measurement of journal taper. Any taper beyond 0.2mm is a sign of excess wear on the journal; the crankshaft must be replaced.



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Fig. Fig. 7: Measure each journal at its outer points to determine taper

BEARING REPLACEMENT



  1. With the engine out of the car and inverted on a stand, remove the main bearing caps in the correct sequence, following procedures given earlier in this section.
  2.  
  3. Once the bearing caps are removed, the lower bearing shell may be inspected. Check closely for scoring or abrasion of the bearing surface. If this lower bearing is worn or damaged, both the upper and lower half should be replaced.
  4.  

Always replace bearing shells in complete pairs.

  1. If the lower bearing half is in good condition, the upper shell may also be considered usable.
  2.  
  3. The bearing shells, the crank throws and the flat surface of the engine block (on the oil pan face) are stamped with numbers (1 through 5) indicating the standard bearing size. This size is determined during the initial manufacturing and assembly process; replacement bearings must be of the same code (thickness) if the correct clearances are to be maintained.If the code on the bearing shell is unreadable, use the number on the block and the number on the crank throw to determine the bearing code. Refer to the proper selection chart to find the correct bearing for that position.
  4.  



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Fig. Fig. 8: Location of main bearing codes



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Fig. Fig. 9: Main bearing selection table - 1985-88 VIN Code 4 and 1988 VIN Code 5 engine



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Fig. Fig. 10: Main bearing selection table - 1989-90 VIN Code 6 engine

  1. Lift the crankshaft from the engine block and remove the upper bearing shells. Clean the area thoroughly, allow the surfaces to air dry and coat all the journals with a liberal coating of clean engine oil.
  2.  
  3. Coat the new bearings to be installed with clean engine oil and install them in the block. Carefully place the crankshaft in position.
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  5. Do not oil the lower bearing shells or the caps at this time. Install the bearing shells into the clean, dry caps.
  6.  
  7. Place a piece of plastic gauging material (such as Plastigage® or similar) lengthwise (fore-and-aft) across the full width of each of the 5 crankshaft main bearing journals. Remember that the measuring material is dissolved by oil. Keep the exposed part of the crank clean and dry.
  8.  
  9. Install the bearing caps with their bearing shells in their correct location and with the arrows pointing towards the front of the motor.
  10.  
  11. Install the bearing cap bolts and tighten them in 3 passes and in the correct sequence to 44 ft. lbs.
  12.  


WARNING
Do not rotate the crankshaft with the measuring plastic installed.

  1. Observing the correct removal sequence, gradually loosen and remove the bearing cap bolts. Carefully remove the bearing caps; the measuring media will be stuck to either the inside of the bearing shell or the face of the crankshaft.
  2.  
  3. Using the scale provided with the package of the measuring media, measure the gauging material at its widest point. This measurement represents the main bearing oil clearance and should be checked against the Crankshaft and Connecting Rod Specifications chart at the beginning of this section.
  4.  
  5. Remove every piece of the plastic gauging material from the crank and bearing caps. Coat the lower bearings (in the caps) with clean motor oil.
  6.  
  7. Install the main bearing caps and the lower throughst washers in the proper sequence. Make sure the arrows on the caps point towards the front (pulley end) of the motor.
  8.  
  9. Tighten the cap bolts in 3 passes and in the correct sequence to 44 ft. lbs.
  10.  
  11. Double check the end-play of the crank by repeating step 10 of this procedure.
  12.  
  13. Turn the crankshaft through 1 or 2 full clockwise rotations, making sure that it turns smoothly and evenly with no binding.
  14.  

 
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