GM Storm/Spectrum 1985-1993 Repair Guide

Crankshaft and Main Bearings

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REMOVAL & INSTALLATION



See Figures 1, 2, 3 and 4

  1. Remove the engine assembly from the vehicle and install on a suitable workstand.
  2.  
  3. Remove the timing belt, oil pan, oil pump, cylinder head and the rear main seal retainer. Refer to the procedures earlier in this section.
  4.  
  5. Remove the piston and connecting rod assemblies. Refer to the procedure in this section.
  6.  
  7. Position a dial indicator at the end of the crankshaft assembly to measure thrust clearance. Carefully pry the crankshaft assembly back and forth with a small prybar and measure the clearance. If the measurement is greater than 0.0118 in. (0.30mm), the thrust washers must be replaced during assembly.
  8.  
  9. Make sure the main bearing caps are numbered so they can be reinstalled in their original positions. Uniformly loosen and remove the bolts in the proper sequence, then remove the bearing caps. If necessary loosen the caps with light blows from a plastic hammer.
  10.  

The bearing caps are loosened from the inside working outward on DOHC engines. The sequence is reversed (from the outward working inside) on SOHC engines.

  1. Position a dial indicator to check crankshaft run-out. Turn the crankshaft and measure run-out; it should not be greater than 0.0039 in. (0.1mm) or the crankshaft must be replaced.
  2.  
  3. Lift the crankshaft from the cylinder block. Inspect the crankshaft and bearings and repair and/or replace as necessary.
  4.  

To install:
  1. After cleaning, inspecting and measuring the crankshaft and checking the main bearing clearance, install the crankshaft. Apply engine assembly lube or clean engine oil to the upper bearing shells prior to installation.
  2.  
  3. Apply engine assembly lube or clean engine oil to the lower bearing shells, then install the main bearing caps in their original positions. Make sure the arrow on the caps is pointing towards the front of the engine. Tighten the bolts in several passes of the proper torque sequence to specification. The torque sequence is the reverse of the removal sequence.
  4.  
  5. After each cap is tightened, check to see and feel that the crankshaft can be rotated by hand. If not, remove the bearing cap and check for the source of the interference.
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  7. When the caps are all installed, recheck thrust clearance and replace the thrust washers, if clearance is greater than maximum.
  8.  
  9. Install the piston and connecting rod assemblies.
  10.  
  11. Install the rear main seal retainer, cylinder head, oil pump, oil pan and the timing belt.
  12.  
  13. Install the engine assembly to the vehicle.
  14.  



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Fig. Fig. 1: Checking crankshaft thrust clearance



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Fig. Fig. 2: Checking crankshaft run-out



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Fig. Fig. 3: Main bearing cap removal sequence - SOHC engines



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Fig. Fig. 4: Main bearing cap removal sequence - DOHC engines

CLEANING AND INSPECTION



See Figure 5

  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 and run-out was not checked prior to removal, check journal run-out. Support the crankshaft in V-blocks and check run-out using a dial indicator. If run-out is greater than 0.0039 in. (0.1mm), the crankshaft must be replaced.
  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. The crankshaft must be replaced if the main bearing journal diameter is less than 1.867 in. (47.418mm) for the 1.5L engines or less than 2.0436 in. (51.908mm) for the 1.6L and 1.8L engines. Refer the Piston and Connecting Rods procedure earlier in this section for crankshaft rod journal measurements.
  8.  
  9. Compare the wear measurements of the various journals. The uneven wear limit across similar journals (compare connecting rod-to-connecting rod journal and main bearing-to-main bearing journal measurements) is 0.00196 in. (0.05mm) for the 1.5L and 1.6L engines or 0.0002 in. (0.005mm) for the 1.8L engine.
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  11. If the crankshaft fails any inspection for wear or damage, it must be reground or replaced.
  12.  



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Fig. Fig. 5: Measure the crankshaft main bearing and connecting rod journals

BEARING REPLACEMENT



See Figure 6

  1. Inspect the bearings for scoring, chipping or other wear.
  2.  
  3. Inspect the crankshaft journals as detailed in the Cleaning and Inspection procedure.
  4.  
  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. Temporarily position the crankshaft in the block with the upper bearings installed.
  6.  

The journal surfaces and bearing shells must be completely free of oil to get an accurate reading with Plastigage® or an equivalent plastic-type measurement device.

  1. Place a strip of Plastigage®, or an equivalent plastic-type measurement device, lengthwise along the center of the crankshaft main bearing journal or lower bearing shell, then install the cap with the shell and torque the connecting rod nuts or main cap bolts to specification. Do not turn the crankshaft with the Plastigage® installed in the bearing.
  2.  
  3. Remove the bearing cap with the shell. The flattened Plastigage® will either be sticking to the bearing shell or the crankshaft journal.
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  5. Using the printed scale on the Plastigage® package, measure the flattened Plastigage® 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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  7. Compare your findings with the bearing clearance specification. If the bearing clearance is greater than 0.0047 in. (0.12mm), the bearing must be replaced with an oversized component. If clearance is less than specification, and bearing substitutions do not correct the problem, the crankshaft must be ground or replaced.
  8.  

Bearing shell sets over standard size are available to correct excessive bearing clearance.

  1. After clearance measuring is completed, be sure to remove the Plastigage® from the crankshaft and/or bearing shell.
  2.  
  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 bearing shell tangs are seated in the notches.
  4.  

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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Fig. Fig. 6: Use a plastic-type measuring device to check main bearing oil clearance

 
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