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    GM Metro/Sprint 1985-1993 Repair Guide

    Crankshaft and Main Bearings

    Print

    REMOVAL and INSTALLATION

    See Figures 1, 2, 3 and 4

    This procedure assumes that the engine has been removed from the vehicle and disassembled. However, it is possible to remove the crankshaft with the engine in the vehicle.



    Click image to see an enlarged view

    Fig. Fig. 1: Correct installation of connecting rod bearing caps



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    Fig. Fig. 2: Upper main bearing installed in cylinder block



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    Fig. Fig. 3: Main bearing cap installation with arrows facing crankshaft pulley side of engine



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    Fig. Fig. 4: Measuring main bearing clearance using Plastigage®

    1. Remove the flywheel and mount the engine onto a workstand.
    2.  
    3. Rotate the crankshaft, until the timing marks on the sprockets align with each other, then remove the timing belt and timing sprocket from the crankshaft.
    4.  
    5. Drain the oil, remove the oil pan and oil pump.
    6.  
    7. Inspect the connecting rods and bearing caps for identification numbers. If there are none, mark them for reassembly purposes.
    8.  
    9. 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.
    10.  
    11. Inspect the main bearing caps for identification numbers. If there are none, mark them for reassembly purposes.
    12.  
    13. Remove the main bearing caps and store them in order, for reassembly purposes. The caps must be reinstalled in their original position.
    14.  
    15. Remove the rear main seal.
    16.  
    17. Remove the crankshaft and main bearing inserts.
    18.  

    To install:
    1. Check the crankshaft for damage or excessive wear. Measure all crankshaft bearing journal dimensions and, as necessary, deliver the crankshaft to a machine shop for regrinding.
    2.  
    3. Using solvent, clean all of the parts and dry thoroughly.
    4.  
    5. Install the upper bearing inserts into the engine.
    6.  
    7. Carefully install the crankshaft and main caps with new lower inserts.
    8.  
    9. Check crankshaft bearing clearance using Plastigage®.
    10.  
    11. If bearing clearances are within specification, remove the the crankshaft and lubricate crankshaft and bearing inserts thoroughly.
    12.  
    13. Reinstall crankshaft and tighten main bearing cap bolts snug. At this point, do not tighten main bearing cap bolts to specification.
    14.  
    15. Using a feeler gauge and a medium pry bar, move the crankshaft forward-and-rearward. Check the crankshaft end-play by inserting a feeler gauge between the crankshaft and the third main bearing (thrust bearing) shell.
    16.  
    17. 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.
    18.  
    19. Tighten main bearing cap bolts to 36-41 ft. lbs.. (50-56 Nm).
    20.  
    21. Install connecting rod caps and check bearing clearance in the same manner as for main bearing inserts.
    22.  
    23. If connecting rod bearing clearance is within specification, lubricate connecting rods and bearing inserts. Tighten connecting rod bearing cap nuts to 24-26 ft. lbs.. (33-35 Nm).
    24.  
    25. Check connecting rod side clearance by inserting a feeler gauge between the side of the rod and the crankshaft. If not within specification, repair as necessary.
    26.  
    27. Rotate the crankshaft, until the timing marks on the sprockets align with each other, then install the timing belt on the engine.
    28.  

    CLEANING, INSPECTION AND BEARING REPLACEMENT



    See Figures 2, 3 and 4

    Replacement bearings are available in standard size and undersize (for reground crankshafts). Check the back of the existing bearing inserts to determine the undersize, if any, of the existing bearings.

    Connecting rod-to-crankshaft bearing clearance is checked using Plastigage® at either the top or the bottom of each crank journal. The Plastigage® has a range of 0.001-0.003 inch(0.0254-0.0762mm).

    1. Remove the crankshaft main bearing cap. Completely clean the bearing shell and the crank journal. Blow any oil from the oil hole in the crankshaft.
    2.  

    Plastigage® will dissolve in oil or solvent. The components being checked must be dry and completely free of dirt, oil and solvent prior to checking the bearing clearance.

    1. Place the Plastigage® lengthwise along the center of the crankshaft journal, then install the cap with the shell and torque nuts to 36-41 ft. lbs.. (50-56 Nm).
    2.  

    Do not turn the crankshaft with the Plastigage® on the bearing.

    1. Remove the bearing cap with the shell. The flattened Plastigage® will be found sticking to either the bearing shell or the crank journal. Do not remove the Plastigage® until measuring it with the scale on the package.
    2.  
    3. Use the scale printed on the Plastigage® envelope to measure the flattened material at its widest point. The number within the scale which most closely corresponds to the width of the Plastigage® indicates the bearing clearance in thousandths of an inch.
    4.  
    5. Compare the measurement to specifications and replace the bearing if clearance is not within range. However, if the bearing is within specification and in good condition, bearing replacement is not necessary.
    6.  
    7. If the crankshaft is in good condition, install new standard size bearings and check the clearance again. If clearance is not within specification, undersize bearings are available.
    8.  
    9. After all measurements have been made, remove the crankshaft and lubricate the crankshaft and bearings.
    10.  
    11. Reinstall the crankshaft and tighten main bearing cap bolts to 36-41 ft. lbs.. (50-56 Nm).
    12.  

     
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