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    GM Chevy Mid-Size Cars 1964-1988 Repair Guide

    Rear Main Oil Seal

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    REMOVAL & INSTALLATION



    All Gasoline Engines Through 1985 (Except 231)

    See Figures 1, 2, 3 and 4

    1. Remove the oil pan from the engine. For details, refer to the oil pan procedures earlier in this section.
    2.  
    3. Remove the oil pump and the rear main bearing cap.
    4.  
    5. Using a small pry bar, carefully pry the oil seal from the rear main bearing cap.
    6.  
    7. Using a small hammer and a brass pin punch, drive the top half of the oil seal from the rear main bearing. Drive it out far enough, so it may be removed with a pair of pliers.
    8.  
    9. Using a non-abrasive cleaner, clean the rear main bearing cap and the crankshaft.
    10.  

    To install:
    1. Fabricate an oil seal installation tool from 0.004 in. shim stock, shape the end to 1 / 2 in. long by 1 / 64 in. wide.
    2.  



    Click image to see an enlarged view

    Fig. Fig. 1: Dimensions for making an oil seal installation tool



    Click image to see an enlarged view

    Fig. Fig. 2: Removing the lower rear main seal from the bearing cap



    Click image to see an enlarged view

    Fig. Fig. 3: Removing the upper rear main seal

    1. Coat the new oil seal with engine oil; DO NOT coat the ends of the seal.
    2.  
    3. Position the fabricated tool between the crankshaft and the seal seat in the cylinder case.
    4.  
    5. Position the new half seal between the crankshaft and the top of the tool, so that the seal bead contacts the tip of the tool.
    6.  

    Make sure that the seal lip is positioned toward the front of the engine.

    1. Using the fabricated tool as a shoe horn, to protect the seal's bead from the sharp edge of the seal seat surface in the cylinder case, roll the seal around the crankshaft. When the seal's ends are flush with the engine block, remove the installation tool.
    2.  
    3. Using the same manner of installation, install the lower half of the seal onto the lower half of the rear main bearing cap.
    4.  
    5. Apply sealant to the cap-to-case mating surfaces and install the lower rear main bearing half to the engine; keep the sealant off of the seal's mating line.
    6.  
    7. Install the rear main bearing cap bolts. Using a lead hammer, tap the crankshaft forward and rearward, to line up the thrust surfaces. Torque the main bearing bolts to specification.
    8.  
    9. If not done already, install the oil pump
    10.  
    11. Install the oil pan and properly refill the engine crankcase.
    12.  



    Click image to see an enlarged view

    Fig. Fig. 4: Packing the rear main oil seal

    1986-88 Gasoline Engines (One Piece Seal)

    See Figures 5 and 6

    1. Remove the transmission assembly from the vehicle. Refer to Drive Train of this guide for removal procedures.
    2.  
    3. Using the notches provided in the rear seal retainer, carefully pry out the seal using a small tool.
    4.  

    Extreme care should be taken when removing the seal so as not to nick and damage the crankshaft sealing surface.

    To install:
    1. Before installation lubricate the new seal with clean engine oil.
    2.  
    3. Install the seal on J-3561 or an equivalent seal installation tool. Thread the tool into the rear of the crankshaft and tighten the screws snugly, this is to insure that the seal will be installed squarely over the crankshaft. With the tool properly positioned, tighten the tool wing nut until it bottoms.
    4.  
    5. Remove the tool from the crankshaft.
    6.  
    7. Install the transmission assembly to the vehicle.
    8.  



    Click image to see an enlarged view

    Fig. Fig. 5: Carefully pry the seal from the retainer at these locations



    Click image to see an enlarged view

    Fig. Fig. 6: One piece seal installation tool

    ONE PIECE SEAL RETAINER AND GASKET
    1. Remove the transmission assembly from the vehicle. Refer to Drive Train of this guide for removal procedures.
    2.  
    3. Remove the oil pan bolts, then lower the oil pan from the engine.
    4.  
    5. Remove the retainer and seal assembly.
    6.  
    7. Remove the gasket and seal from the retainer assembly.
    8.  

    Whenever the retainer is removed a new retainer gasket and rear main seal must be installed.

    To install:
    1. Thoroughly clean the gasket mating surfaces.
    2.  
    3. Position a new gasket, then install and secure the seal retainer.
    4.  
    5. Install the oil pan and tighten the retainers.
    6.  
    7. Install a new one piece seal to the retainer using a suitable installation tool.
    8.  
    9. Install the transmission assembly to the vehicle.
    10.  

    231 V6

    See Figures 7 and 8

    On this engine, the upper half of the rear main bearing oil seal may be repaired, but not replaced, with the crankshaft installed in the block. To completely replace the seal, the crankshaft must be removed. The lower part of the seal may be replaced in the conventional manner when the bearing cap is removed.

    Place the new bearing cap neoprene seals in kerosene for two minutes before installing them. The neoprene seals will swell up once exposed to the oil and heat when in the engine. It is normal for the seals to leak for a short time, until they become properly seated. The neoprene seals must NOT be cut to fit.

    1. Remove the oil pan and the rear main bearing cap.
    2.  
    3. Using a blunt-edged tool, drive the upper seal into its groove until it is tightly packed. This is usually a distance of 1 / 4 - 3 / 4 in.
    4.  
    5. Cut pieces of a new seal 1 / 16 in. longer than required to fill the grooves and install them, packing them into place.
    6.  
    7. Carefully trim any protruding edges of the fabric seal. Do NOT cut the neoprene seals on the bearing cap.
    8.  
    9. Remove the old seal from the bearing cap, and install a new seal.
    10.  

    To help eliminate oil leakage at the joint where the cap meets the crankcase, apply RTV type sealer to the rear main bearing cap split line. When applying sealer, use only a thin coat as an over abundance will not allow the cap to seat properly.

    1. Reinstall the cap and the oil pan.
    2.  



    Click image to see an enlarged view

    Fig. Fig. 7: DO NOT over-apply sealant to the lower main bearing cap-231 V6



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    Fig. Fig. 8: The new lower seal may be rolled into position

    Diesel

    See Figures 9



    Click image to see an enlarged view

    Fig. Fig. 9: Use the bearing cap as a holding fixture when cutting off lengths of the old seal

    The crankshaft need not be removed to replace the rear main bearing upper oil seal. The lower seal is installed in the bearing cap.

    1. Drain the crankcase oil and remove the oil pan, then remove the rear main bearing cap.
    2.  
    3. Using a special main seal tool or a tool that can be made from a dowel (see illustration), drive the upper seal into its groove on each side until it is tightly packed. This is usually 1 / 4 - 3 / 4 in.
    4.  
    5. Measure the amount the seal was driven up on one side; add 1 / 16 in and cut this length from the old seal that was removed from the main bearing cap. Use a single-edge razor blade. Measure the amount the seal was driven up on the other side; add 1 / 16 in. and cut another length from the old seal. Use the main bearing cap as a holding fixture when cutting the seal as illustrated. Carefully trim the protruding seal.
    6.  
    7. Work these two pieces of seal up into the cylinder block on each side with two nail sets or small screwdrivers. Using the packing tool again, pack these pieces into the block, then trim them flush with a razor blade or hobby knife. Do not scratch the bearing surfaces with the razor.
    8.  
    9. Install a new seal in the rear main bearing cap. Run a 1 / 16 in. bead of sealer onto the outer mating surface of the bearing cap. Install the cap to the block and torque to specification.
    10.  
    11. Install the oil pan and properly refill the crankcase with clean engine oil.
    12.  

     
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