GM Full-Size Trucks 1970-1979 Repair Guide

Intake Manifold

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REMOVAL & INSTALLATION



Inline 6-Cylinder

1974 and earlier 250 and 292 6-cylinder engines use a combined intake and exhaust manifold, both of which are removed together. 1976 and later engines have an intake manifold which is cast integrally with the cylinder head and cannot be removed.

  1. Disconnect the negative battery cable.
  2.  
  3. Remove the air cleaner assembly and air ducts.
  4.  
  5. Tag and disconnect the throttle linkage at the carburetor. Tag and disconnect the fuel line, vacuum lines, hoses, and electrical connections.
  6.  
  7. Disconnect the transmission downshift linkage (if equipped), and remove the PCV valve from the rocker cover. On models equipped with air injection, disconnect the air supply hose from the check valve on the air injection manifold.
  8.  
  9. Remove the carburetor, with spacer and heat shield (if equipped).
  10.  
  11. Spray the nuts and bolts connecting the exhaust manifold to the exhaust pipe with a rust penetrant, as these are usually quite difficult to remove. Unbolt the exhaust manifold from the pipe.
  12.  

It may be necessary to remove the generator rear bracket and/or air conditioning compressor bracket on some models.

  1. Unbolt the manifold bolts and clamps, and remove the manifold assembly.
  2.  
  3. If you intend to separate the manifolds, remove the single bolt and two nuts at the center of the manifold assembly.
  4.  
  5. Installation is the reverse of removal. When assembling the manifolds, install the connecting bolts loosely first. Place the manifolds on a straight, flat surface and hold them securely during tightening, this assures the proper mating of surfaces when the manifold assembly is fastened to the head. Stress cracking could occur if the manifolds are not assembled first in this manner. On all manifolds, always use new gaskets between the manifold and cylinder head.
  6.  

V6 and V8 Engines
EXCEPT DIESEL ENGINES

See Figures 1, 2, 3, 4, 5, 6, 7 and 8



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Fig. Fig. 1: Unfasten the intake manifold retaining bolts ...



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Fig. Fig. 2: ... then remove the intake manifold from the engine



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Fig. Fig. 3: Carefully clean the gasket mating surfaces, using a suitable gasket scraper



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Fig. Fig. 4: Intake manifold bolt tightening sequence - V6 engines



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Fig. Fig. 5: Intake manifold bolt tightening sequence - 305 and 350 V8 engines



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Fig. Fig. 6: Intake manifold bolt tightening sequence - 454 V8 engines



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Fig. Fig. 7: On small-blocks, run a 3/16 in. bead of RTV sealer across the block and 1/2 in. up the sides of the block just before manifold installation



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Fig. Fig. 8: Intake manifold removal and installation - V6 engine shown

  1. Disconnect the negative battery cable.
  2.  
  3. Drain the cooling system.
  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 assembly.
  2.  
  3. Remove the thermostat housing and the bypass hose. It is not necessary to remove the top radiator hose from the thermostat housing.
  4.  
  5. Disconnect the heater hose at the rear of the manifold.
  6.  
  7. Detach all electrical connections and vacuum lines from the manifold. Remove the EGR valve if necessary.
  8.  
  9. On vehicles equipped with power brakes remove the vacuum line from the vacuum booster to the manifold.
  10.  
  11. Remove the distributor (if necessary).
  12.  
  13. Move the air conditioning compressor to one side, if necessary.
  14.  
  15. Relieve the fuel system pressure. See Fuel System .
  16.  
  17. Disconnect the fuel line from the carburetor.
  18.  
  19. Remove the carburetor linkage.
  20.  
  21. Remove the carburetor, if necessary.
  22.  
  23. Unfasten the intake manifold bolts. Remove the manifold and the gaskets.
  24.  
  25. Thoroughly clean the gasket mating surfaces.
  26.  

To install:
  1. Remember to reinstall the O-ring seal between the intake manifold and timing chain cover during assembly, if so equipped.
  2.  
  3. Installation is the reverse of the removal procedure. Make sure to use the correct bolt tightening sequence.
  4.  
  5. Reconnect all wires, hoses and linkage. Use plastic gasket retainers to prevent the manifold gasket from slipping out of place, if so equipped.
  6.  
  7. On the small block V8s, place a 1 / 6 in. bead of RTV type silicone sealer on the front and rear ridges of the cylinder block-to-manifold mating surfaces. Extend the bead 1 / 2 in. up each cylinder head to seal and retain the manifold side gaskets.
  8.  

Before installing the intake manifold, be sure that the gasket surfaces are thoroughly clean.

DIESEL ENGINES

See Figures 9, 10, 11, 12, 13, 14, 15 and 16



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Fig. Fig. 9: View of the diesel engine intake manifold installation. Note the sealer application



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Fig. Fig. 10: Intake manifold bolt tightening sequence - 350 V8 diesel engine



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Fig. Fig. 11: Diesel engine intake manifold drain tube



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Fig. Fig. 12: Oil pump drive and vacuum pump - 350 diesel engine



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Fig. Fig. 13: Adapter and seal details - 350 diesel engine



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Fig. Fig. 14: The index mark on the injection pump driven gear will be offset to the right when the No. 1 cylinder is at TDC