Chrysler Full-Size Trucks 1967-1988 Repair Guide

Combination Manifold

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A combination manifold is a sandwiched intake and exhaust manifold secured with screws, installed on many inline 6 cylinder gasoline engines. Although it is called a combination manifold, with the assembly sandwiching hardware unfastened, the combination manifold can be separated to reveal both an intake portion as well as an exhaust manifold section.

REMOVAL & INSTALLATION



See Figure 1

Inline 6 Cylinder Gasoline Engines
EXCEPT 251
  1. Disconnect the negative battery cable.
  2.  
  3. Disconnect the air cleaner vacuum line from the carburetor, then the flexible connector between the air cleaner and carburetor air heater.
  4.  
  5. Disconnect the crankcase inlet air cleaner to air cleaner hose and remove the air cleaner assembly and set aside.
  6.  
  7. Tag then disconnect the distributor vacuum line, crankcase ventilator valve hose and carburetor bowl vent line. (If equipped).
  8.  
  9. Remove the carburetor air heater. Tag and disconnect the fuel line, throttle linkage, and automatic choke rod from the carburetor. Remove the carburetor.
  10.  
  11. Disconnect the exhaust manifold at the flange where it mates to the exhaust downpipe.
  12.  
  13. Detach the exhaust manifold by removing the nuts and washers at the cylinder head.
  14.  

Remove the three bolts securing the intake manifold portion to the exhaust manifold section, then carefully separate the manifolds. Slowly remove the exhaust manifold from the engine compartment.

  1. If the intake portion needs to be removed, unfasten the retaining hardware securing the manifold to the engine. remove the assembly, with carburetor, from the engine compartment.
  2.  
  3. Remove any gasket material left behind on the manifold surface and cylinder head. Clean the manifolds in solvent and dry with compressed air.
  4.  
  5. Inspect the manifold for cracks and flatness; warping can occur and cause a leak. You would need to purchase a new manifold in this case.
  6.  

To install:
  1. Install a new gasket between the exhaust and intake manifolds, coat both sides of the gasket with sealer, if recommended by the gasket manufacturer. Install the long screws holding the manifolds together.
  2.  


CAUTION
When installing the manifolds on the cylinder head of the engine, it is very important the procedure is followed correctly to permit the exhaust manifold to expand and contract with the heating and cooling cycles of normal engine operation, otherwise manifold breakage will occur.

  1. Install the manifold, then washers in place. Washers spanning intake and exhaust flanges must be flat, replace any washers that are distorted.
  2.  
  3. Install the steel conical washer with the cup side facing the nut. Install the brass washer with flat side facing the manifold. Install the nuts with cone side facing the washers.
  4.  
  5. Carefully snug all intake-to-exhaust manifold bolts and manifold-to-cylinder headnuts. Snug all nuts and bolts to 10 inch lbs. (1 Nm). DO NOT OVERTIGHTEN.
  6.  
  7. Tighten inboard intake-to-exhaust manifold bolts to 20-23 ft. lbs. (27-31 Nm).
  8.  
  9. Tighten outboard intake-to-exhaust manifold bolts to 20-23 ft. lbs. (27-31 Nm).
  10.  
  11. Repeat the tightening procedures 14 through 16 until all two/three manifold bolts are at specified torque.
  12.  



Click image to see an enlarged view

Fig. Fig. 1: Combination Manifold torque sequence

  1. Tighten the manifold-to-cylinder head nuts to 120 inch lbs. (14 Nm), in tightening sequence shown. DO NOT OVERTIGHTEN .
  2.  
  3. Attach the exhaust pipe-to-manifold flange, with new gasket, tighten all stud nuts to 35 ft. lbs. (47 Nm).
  4.  
  5. Install the carburetor air heater.
  6.  
  7. Install air injection tube with gasket and tighten to 17 ft. lbs. (23 Nm). Install carburetor, all fuel lines, automatic choke rod, and throttle linkage.
  8.  
  9. Install air cleaner and connect the crankcase inlet air cleaner to air cleaner hose. Install any lines carb and air system left.
  10.  
  11. Connect the negative battery cable.
  12.  

251 ENGINE

See Figure 2

  1. Disconnect the negative battery cable.
  2.  
  3. Remove the air cleaner, followed by all the lines and tubes from the carburetor.
  4.  
  5. Disconnect all the linkages to the carburetor and remove the carburetor from the manifold assembly.
  6.  
  7. Disconnect the exhaust pipe from the manifold, remove the manifold attaching washers and retaining nuts, then remove the manifold from the cylinder head.
  8.  



Click image to see an enlarged view

Fig. Fig. 2: 6-251 Manifold view

  1. Separate the exhaust manifold from the intake manifold, if necessary, and install a new gasket between the two upon re-assembly. Torque the bolts to 25 ft. lbs. (34 Nm).
  2.  

Do not tighten the three securing bolts until the manifold assembly has been installed on the cylinder head.

To install:
  1. Position the manifold on the cylinder head using a new gasket, then install the conical and triangular washers, along with the retaining nuts, and torque the retaining nuts and the three securing bolts to 20 ft. lbs. (27 Nm) in a spiral sequence from the center to the ends.
  2.  
  3. Attach the exhaust pipe to the exhaust manifold flange. Torque the nuts to 30 ft. lbs. (41 Nm).
  4.  
  5. Install the carburetor then attach all the lines, tubes, and linkages. Install the air cleaner assembly.
  6.  
  7. Connect the negative battery terminal.
  8.  

 
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