GM Full-Size Trucks 1980-1987 Repair Guide

Cylinder Head

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REMOVAL & INSTALLATION



In-line 6-Cylinder

See Figure 1

  1. Disconnect the negative battery cable.
  2.  
  3. Drain the cooling system and remove the air cleaner assembly. Disconnect the PCV hose.
  4.  


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.

  1. Tag and disconnect the throttle linkage at the carburetor. Tag and disconnect the fuel line, vacuum lines, and any electrical connections at the carburetor.
  2.  
  3. Remove the top radiator hose, and the battery ground strap. Disconnect the wires from the temperature sending unit, leaving the harness clear of the clips on the rocker cover.
  4.  
  5. Disconnect the coil wires after tagging them, and remove the coil. Tag and disconnect the spark plug wires from the plugs.
  6.  
  7. Remove the intake and exhaust manifolds.
  8.  

On the 250 (4.1L) engine, the intake manifold is an integral part of the cylinder head.

  1. Remove the rocker arm cover. Back off the rocker arm nuts, and pivot the rocker arms so the pushrods will clear.
  2.  
  3. Take a piece of heavy cardboard and cut 12 holes in it the same diameter as the pushrod stem. Number the holes in relation to the pushrods being removed. This cardboard holder will keep the pushrods in order (and hopefully out of harms way) while they are out of the engine. Remove the pushrods one at a time.
  4.  

Pushrods MUST be returned to their original locations.

  1. Remove the cylinder head bolts one at a time, and mark them or keep them in order, as they should go back in their original locations. You may need a flex bar on your socket, or a piece of pipe on your ratchet, as the bolts are under a lot of torque.
  2.  
  3. Remove the cylinder head, along with the gasket. If the head seems stuck to the block, gently tap around the edge of the head with a rubber mallet until the joint breaks. NEVER pry between the head and block as you may gouge one or the other. Often it is necessary to carefully scrape the top of the engine block and the cylinder head to completely remove the gasket.
  4.  
  5. Clean the bottom of the head and top of block thoroughly before reinstalling the head. Place a new gasket over the dowel pin in the top of the block.
  6.  

Different types of head gaskets are available. If you are using a steel/asbestos composition gasket, do not use gasket sealer.

  1. Lower the cylinder head carefully onto the block, over the dowel pins and gasket.
  2.  
  3. Coat the heads and threads of the cylinder head bolts with sealing compound, GM part No. 1052080 or equivalent, and install finger tight.
  4.  
  5. Tighten the heads bolts gradually in three stages, following the sequence illustrated, to the specification listed under Torque Specifications.
  6.  
  7. Install the pushrods in the exact location from which they were removed. Make sure they are seated in their lifter sockets.
  8.  
  9. Swing the rocker arms over into the correct position. Tighten the rocker arms until all pushrod play is taken up.
  10.  
  11. Install the manifold assembly, using new gaskets. Torque the manifold(s) to the specified torque.
  12.  
  13. Reverse the remainder of the removal procedure for installation. Adjust the valves, following the procedure in this Section. Use a new gasket or high temperature sealer when installing the rocker arm cover.
  14.  



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Fig. Fig. 1: 250 and 292 six cylinder head bolt torque sequence

Gasoline V6 and V8s

See Figures 2, 3, 4, 5, 6, 7, 8 and 9

  1. Disconnect the negative battery cable.
  2.  
  3. Drain the coolant and save it if still fresh.
  4.  


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.

  1. Remove the air cleaner.
  2.  
  3. Remove the air conditioning compressor, but do not disconnect any air conditioning lines. Secure the compressor to one side.
  4.  



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Fig. Fig. 2: When removing either of the cylinder heads, you must first remove the intake manifold assembly



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Fig. Fig. 3: Disconnect and reposition the exhaust manifold from the cylinder head that is being removed



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Fig. Fig. 4: Loosen the retainers and remove the valve covers from the cylinder head(s) being removed

  1. Disconnect the AIR hose at the check valve.
  2.  
  3. Remove the intake manifold.
  4.  
  5. When removing the right cylinder head, loosen the alternator belt, disconnect the wiring and remove the alternator.
  6.  
  7. When removing the left cylinder head, remove the dipstick, power steering pump and air pump if so equipped.
  8.  
  9. Label the spark plug wires and disconnect them.
  10.  
  11. Disconnect the exhaust manifold from the head being removed and reposition the manifold aside.
  12.  
  13. Remove the valve cover. Scribe the rocker arms with an identifying mark for reassembly; it is important that the rocker assembly is reinstalled in the same position as it was removed. Remove the rocker arm nuts, rocker arms and pivots.
  14.  



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Fig. Fig. 5: Loosen and remove the cylinder head bolts using a large ratchet or breaker bar and suitably sized socket

  1. Take a piece of heavy cardboard and cut 12 (V6), 16 holes (V8) (or half the number of holes if you are only removing one head) in it the same diameter as the pushrod stem. Number the holes in relation to the pushrods being removed. This cardboard holder will keep the pushrods in order (and hopefully out of harm's way) while they are out of the engine. Remove the pushrods.
  2.  

Pushrods MUST be returned to their original locations.

  1. On models equipped with power brakes, it may be necessary to disconnect the brake booster and turn it sideways to remove the No.7 pushrod.
  2.  
  3. Check to make sure all wires are disconnected from the cylinder head.
  4.  
  5. Remove the cylinder head bolts, and remove the cylinder head and gasket. If the head seems stuck to the block, gently tap around the edge of the head with a rubber mallet until the joint breaks.
  6.  



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Fig. Fig. 6: Remove the old gasket from the engine block and discard

To install:
  1. Position a new cylinder head gasket, then install the cylinder head to the engine block.
  2.  
  3. Coat the threads of the cylinder head bolts with sealing compound, GM part No. 1052080 or equivalent, and install finger-tight.
  4.  
  5. Tighten the bolts to specification using the proper torque sequence. For proper torque specification, refer to the chart located earlier in this section.
  6.  

When installing the intake manifold remember to use new gaskets.

  1. Reverse the removal procedure to complete installation. Be sure to install the rocker arms and push rods in their original positions. Adjust the valves as outlined earlier.
  2.  



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Fig. Fig. 7: Small-block V8 cylinder head torque sequence



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Fig. Fig. 8: Big-block V8 torque sequence



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Fig. Fig. 9: V6 262 cylinder head torque sequence

Diesel Engines

See Figure 10

  1. Disconnect the negative battery cable.
  2.  
  3. Remove the intake manifold, using the procedure outlined above.
  4.  
  5. Remove the rocker arm cover(s), after removing any accessory brackets which interfere with cover removal.
  6.  
  7. Disconnect and label the glow plug wiring.
  8.  
  9. If the right cylinder head is being removed, remove the ground strap from the head.
  10.  
  11. On the 350, remove the rocker arms bolts, the bridged pivots, the rocker arms, and the pushrods, keeping all the parts in order so that they can be returned to their original positions. On the 379, remove the rocker shaft assemblies. It is a good practice to number or mark the parts to avoid interchanging them.
  12.  
  13. Remove the fuel return lines from the nozzles.
  14.  
  15. Remove the exhaust manifold(s), using the procedure outlined earlier in this Section.
  16.  
  17. On the 8-350, remove the engine block drain plug on the side of the engine from which the cylinder head is being removed.
  18.  
  19. Remove the head bolts. Remove the cylinder head.
  20.  
  21. To install, first clean the mating surfaces thoroughly. Install new head gaskets on the engine block. DO NOT coat the gaskets with any sealer on the either engine. The gaskets have a special coating that eliminates the need for sealer. The use of sealer will interfere with this coating and cause leaks. Install the cylinder head onto the block.
  22.  
  23. Clean the head bolts thoroughly. On the 350, dip the bolts in clean engine oil and install them into the cylinder block until the heads of the bolts lightly contact the cylinder head. On the 379, the left rear head bolt must be installed into the head prior to head installation. Coat the threads of the 379 cylinder head bolts with sealing compound (GM part No. 1052080 or equivalent) before installation.
  24.  
  25. On the 350, tighten the bolts in the illustrated sequence to 100 ft. lbs. When all the bolts have been tightened to this figure, begin the tightening sequence again, and torque all bolts to 130 ft. lbs. On the 379, tighten each bolt gradually in the sequence shown until the final torque specified (100 ft. lbs.) is met.
  26.  
  27. Install the engine block drain plugs on the 350, the exhaust manifolds, the fuel return lines, the glow plug wiring, and the ground strap for the right cylinder head.
  28.  
  29. Install the valve train assembly. Refer to the Diesel Engine Rocker Arm Replacement in this Section for the valve lifter bleeding procedures.
  30.  
  31. Install the intake manifold.
  32.  
  33. Install the valve covers. These are sealed with RTV-type silicone sealer instead of a gasket. See the Valve Cover procedure for proper sealer application. Install the cover to the head within 10 minutes, while the sealer is still wet.
  34.  



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Fig. Fig. 10: 379 diesel cylinder head torque sequence

CLEANING AND INSPECTION



See Figure 11

Any diesel cylinder head work should be handled by a reputable machine shop familiar with diesel engines. Disassembly, valve lapping, and assembly can be completed by following the gasoline engine procedures.

Once the complete valve train has been removed from the cylinder head(s), the head itself can be inspected, cleaned and machined (if necessary). Set the head(s) on a clean work space, so the combustion chambers are facing up. Begin cleaning the chambers and ports with a hardwood chisel or other non-metallic tool (to avoid nicking or gouging the chamber, ports, and especially the valve seats). Chip away the major carbon deposits, then remove the remainder of carbon with a wire brush fitted to an electric drill.

Be sure that the carbon is actually removed, rather than just burnished. After decarbonizing is completed, take the head(s) to a machine shop and have the head hot tanked. In this process, the head is lowered into a hot chemical bath that very effectively cleans all grease, corrosion, and scale from all internal and external head surfaces. Also have the machinist check the valve seats and recut them if necessary. When you bring the clean head(s) home, place them on a clean surface. Completely clean the entire valve train with solvent.



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Fig. Fig. 11: Use a wire brush and electric drill to remove carbon from the combustion chamber and exhaust ports

RESURFACING



See Figures 12 and 13

Lay the head down with the combustion chambers facing up. Place a straightedge across the gasket surface of the head, both diagonally and straight across the center. Using a flat feeler gauge, determine the clearance at the center of the straightedge. If warpage exceeds 0.003 inch in a 6 inch span, or 0.006 inch over the total length, the cylinder head must be resurfaced. Resurfacing can be performed at most machine shops.



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Fig. Fig. 12: Check the cylinder head mating surface for warpage using a precision straight edge and a feeler gauge

When resurfacing the cylinder head(s) of V8 engines, the intake manifold mounting position is altered, and must be corrected by machining a proportionate amount from the intake manifold flange.



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Fig. Fig. 13: Be sure to check the head across the center and both diagonals of the mating surface

 
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