GM Full-Size Trucks 1980-1987 Repair Guide

Timing Chain Cover and Front Oil Seal

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REMOVAL & INSTALLATION




CAUTION
When draining the coolant, keep in mind that cats and dogs are attracted by the ethylene glycol antifreeze, and are quite likely to drink any that is left in an uncovered container or in puddles on the ground. This will prove fatal in sufficient quantity. Always drain the coolant into a sealable container. Coolant should be reused unless it is contaminated or several years old.

In-line 6 Cylinder

See Figures 1, 2 and 3

  1. Disconnect the negative battery cable.
  2.  
  3. Drain the engine coolant, remove the radiator hoses, and remove the radiator.
  4.  
  5. Remove the fan belt and any accessory belts. Remove the fan pulley.
  6.  
  7. A harmonic balancer puller is necessary to pull the balancer. Install the puller and remove the balancer.
  8.  
  9. Remove the two screws which attach the oil pan to the front cover. Remove the screws which attach the front cover to the block. Do not remove the cover yet.
  10.  
  11. Before the front cover is removed, it is necessary to cut the oil pan front seal. Pull the cover forward slightly.
  12.  
  13. Using a sharp knife or razor knife, cut the oil pan front seal flush with the cylinder block on both sides of the cover.
  14.  
  15. Remove the front cover and the attached portion of oil pan front seal. Remove the front cover gasket from the block.
  16.  
  17. To install the front cover, first obtain an oil pan front seal. Cut the tabs from the new seal.
  18.  
  19. Install the seal in the front cover, pressing the tips into the holes provided in the cover. Coat the mating area of the front cover with a room temperature vulcanizing (RTV) sealer first.
  20.  
  21. Coat the new front cover gasket with sealer and install it on the cover.
  22.  
  23. Apply a 1 /8 inch bead of RTV sealer to the joint formed at the oil pan and cylinder block.
  24.  
  25. Install the front cover.
  26.  
  27. Install the harmonic balancer. Make sure the front cover seal is positioned evenly around the balancer. If you do not have access to a balancer installation tool (and you probably don't) you can either fabricate one using the illustration as a guide, or you can tap the balancer on using a brass or plastic mallet. If you use the last method, make sure the balancer goes on evenly.
  28.  
  29. The rest of the installation is in the reverse order of removal.
  30.  



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Fig. Fig. 1: Applying sealer front cover mounting on the 250 in-line six



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Fig. Fig. 2: Oil pan front seal modification



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Fig. Fig. 3: Cut the oil pan seal flush with the front of the block

Gasoline V6 and V8s

See Figures 4, 5, 6, 7, 8, 9, 10, 11, 12 and 13

  1. Disconnect the negative battery cable.
  2.  
  3. Drain the cooling system.
  4.  



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Fig. Fig. 4: Remove the retaining bolt and remove the crankshaft pulley



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Fig. Fig. 5: Use a suitable damper puller to remove the crankshaft torsional damper. Do not use a jawed puller as it could damage the damper



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Fig. Fig. 6: Once the damper is loosened, you should be able to pull it free by hand

If the center crankshaft pulley bolt is difficult to remove, spray the bolt with penetrating oil and allow some time to work. Manual transmission vehicles may be placed in gear with an assistant holding the break pedal to give the resistance necessary to break loose the bolt. Automatic transmission vehicles are more difficult, first have an assistant try to hold the pulley or use bolts threaded in the outer holes to hold the pulley steady while the bolt is loosened. If this is not sufficient, a flywheel holding fixture should be used to lock the crankshaft so the bolt may be removed.

  1. Remove the crankshaft pulley and damper, using Tool J-23523 Damper Pulley remover and installer. Remove the water pump. Remove the screws holding the timing case cover to the block and remove the cover and gaskets.
  2.  
  3. Use a suitable tool to pry the old seal out of the front face of the cover.
  4.  
  5. Install the new seal so that the open end is toward the inside of the cover, using Tool J-35468 Seal installer.
  6.  



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Fig. Fig. 7: Remove the timing cover bolts from the cover flange



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Fig. Fig. 8: Once the bolts are removed, a small bit of leverage may be necessary to break the gasket seal

Coat the lip of the new seal with oil prior to installation.

  1. Check that the timing chain oil slinger is in place against the crankshaft sprocket.
  2.  
  3. Apply sealer to the front cover as shown in the accompanying illustration. Install the cover carefully onto the locating dowels.
  4.  



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Fig. Fig. 9: With the gasket seal broken, remove the cover from the front of the engine block



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Fig. Fig. 10: Be sure not to loose the rubber seal located on the bottom of most timing covers

  1. Tighten the attaching screws to 6-8 ft. lbs.
  2.  
  3. Install the damper pulley using Tool J-23523 Damper Pulley installer and torque the retaining bolt to specifications. (See the Torque Specifications Chart). The damper may be installed by partially by hand and the bolt may be used to draw it into position if the fit is not too tight. If necessary, use some steel wool to clean the crankshaft-to-damper mating surfaces of corrosion and allow for a smoother fit.
  4.  



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Fig. Fig. 11: Seal installation with cover installed, V8's



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Fig. Fig. 12: Sealer application



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Fig. Fig. 13: Guiding front cover into place. Be careful seal remains in place

8-350 Diesel

See Figures 14 and 15

  1. Disconnect the negative battery cable.
  2.  
  3. Drain the cooling system and disconnect the radiator hoses.
  4.  
  5. Remove all belts, fan and pulley, crankshaft pulley and balancer, using a balancer puller.
  6.  


WARNING
The use of any other type of puller, such as a universal claw type which pulls on the outside of the hub, can destroy the balancer. The outside ring of the balancer is bonded in rubber to the hub. Pulling on the outside will break the bond. The timing mark is on the outside ring. If it is suspected that the bond is broken, check that the center of the keyway is 16 degrees from the center of the timing slot. In addition, there are chiseled aligning marks between the weight and the hub.

  1. Unbolt and remove the cover, timing indicator and water pump.
  2.  
  3. It may be necessary to grind a flat on the cover for gripping purposes.
  4.  
  5. Grind a chamfer on one end of each dowel pin.
  6.  
  7. Cut the excess material from the front end of the oil pan gasket on each side of the block.
  8.  
  9. Clean the block, oil pan and front cover mating surfaces with solvent.
  10.  
  11. Trim about 1 /8 inch off each end of a new front pan seal.
  12.  
  13. Install a new front cover gasket on the block and a new seal in the front cover.
  14.  
  15. Apply sealer to the gasket around the coolant holes.
  16.  
  17. Apply sealer to the block at the junction of the pan and front cover.
  18.  
  19. Place the cover on the block and press down to compress the seal. Rotate the cover left and right and guide the pan seal into the cavity using a small screwdriver. Oil the bolt threads and install two bolts to hold the cover in place. Install both dowel pins (chamfered end first), then install the remaining front cover bolts.
  20.  
  21. Apply a lubricant, compatible with rubber, on the balancer seal surface.
  22.  
  23. Install the balancer and bolt. Torque the bolt to 200-300 ft. lbs.
  24.  
  25. Install the other parts in the reverse order of removal.
  26.  



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Fig. Fig. 14: Grinding chamfer, 350 diesel dowel pin



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Fig. Fig. 15: Trimming pan seal with razor blade

379 Diesel

See Figures 16, 17 and 18

  1. Disconnect the negative battery cable.
  2.  
  3. Drain the cooling system.
  4.  
  5. Remove the water pump.
  6.  
  7. Rotate the crankshaft to align the marks on the injection pump driven gear and the camshaft gear as shown in the illustration.
  8.  
  9. Scribe a mark aligning the injection pump flange and the front cover.
  10.  
  11. Remove the crankshaft pulley and torsional damper.
  12.  
  13. Remove the front cover-to-oil pan bolts (4).
  14.  
  15. Remove the two fuel return line clips.
  16.  
  17. Remove the injection pump drive gear. Remove the injection pump retaining nuts from the front cover.
  18.  
  19. Remove the baffle. Remove the remaining cover bolts, and remove the front cover.
  20.  
  21. If the front cover oil seal is to be replaced, it can now be pried out of the cover with a suitable prying tool. Press the new seal into the cover evenly.
  22.  

The oil seal can also be replaced with the front cover installed. Remove the torsional damper first, then pry the old seal out of the cover using a suitable prying tool. Use care not to damage the surface of the crankshaft. Install the new seal evenly into the cover and install the damper.

  1. To install the front cover, first clean both sealing surfaces until all traces of old sealer are gone. Apply a 2mm bead of sealant (GM sealant No. 1052357 or equivalent) to the sealing surface as shown in the illustration. Apply a bead of RTV-type sealer to the bottom portion of the front cover which attaches to the oil pan. Install the front cover.
  2.  
  3. Install the baffle.
  4.  
  5. Install the injection pump, making sure the scribe marks on the pump and front cover are aligned.
  6.  
  7. Install the injection pump driven gear, making sure the marks on the cam gear and pump gear are aligned. Be sure the dowel pin and the three holes on the pump flange are also aligned.
  8.  
  9. Install the fuel line clips, the front cover-to-oil pan bolts, and the torsional damper and crankshaft pulley. Torque the pan bolts to 4-7 ft. lbs., and the damper bolt to 140-162 ft. lbs.
  10.  



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Fig. Fig. 16: 379 diesel crankshaft (torsional) damper. Note key



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Fig. Fig. 17: Front cover assembly showing sealer application, 379 diesel



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Fig. Fig. 18: Injection pump and cam gear alignment, 379 diesel

 
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