Exhaust Gasket - Front

Replace the exhaust manifold gaskets on the 390ci V8 engine to eliminate exhaust leaks at the cylinder heads.

Warnings

Tools required

Parts

• Exhaust manifold gasket set (left and right) × 1 — Use OEM specification or Fel-Pro MS90032
• Exhaust manifold bolts (if corroded) × 1 — Use OEM specification

Preparation

1. Ensure engine is completely cold to the touch
2. Disconnect negative battery cable
3. Raise front of vehicle and support securely on jack stands
4. Apply penetrating oil to all visible exhaust manifold bolts and allow to soak
5. Remove air cleaner assembly and note carburetor linkage positions
6. Disconnect any spark plug wires that may interfere with manifold access

Procedure

1. 1

   Disconnect exhaust pipes from manifolds
   Working from underneath the vehicle, locate the exhaust pipe flange connections at both exhaust manifolds. Remove the two bolts securing each exhaust pipe to its respective manifold. You may need to apply additional penetrating oil and use a pipe wrench to hold the pipe while loosening bolts. Support exhaust pipes with wire or blocks to prevent strain on remaining connections.
2. 2

   Remove driver side heat shield and accessories
   Remove any heat shields attached to the driver side exhaust manifold. Disconnect the automatic choke heat tube if equipped. On the driver side, you may need to remove the dipstick tube bracket for clearance.
3. 3

   Remove driver side manifold bolts
   Starting from the center bolts and working outward, remove all exhaust manifold mounting bolts from the driver side. The 390ci V8 typically uses 8 bolts per manifold. Use a universal joint and extensions to access bolts at difficult angles. If a bolt breaks, mark its location for extraction after manifold removal.
4. 4

   Remove driver side exhaust manifold
   Carefully work the driver side exhaust manifold free from the cylinder head studs. It may be necessary to tap the manifold gently with a rubber mallet to break the gasket seal. Lift the manifold away from the engine and set aside on a protected surface.
5. 5

   Remove passenger side heat riser and accessories
   On the passenger side, disconnect the heat riser valve control linkage. Remove any heat shields or brackets. The passenger side typically has more clearance issues due to steering components and engine mounts.
6. 6

   Remove passenger side manifold bolts
   Remove all exhaust manifold mounting bolts from the passenger side manifold. Work carefully around the heat riser valve housing. Note the position of any different length bolts or those with brackets attached.
7. 7

   Remove passenger side exhaust manifold
   Carefully remove the passenger side exhaust manifold with heat riser valve attached. This manifold may be heavier and more awkward to handle due to the heat riser valve assembly. Set aside on a protected surface.
8. 8

   Clean gasket surfaces on cylinder heads
   Using a gasket scraper and wire brush, thoroughly clean all old gasket material from both cylinder head exhaust port surfaces. Take care not to gouge or damage the machined surfaces. Clean each port opening and inspect for cracks or damage. Use a shop vacuum to remove all debris before installing new gaskets.
9. 9

   Clean and inspect manifolds
   Clean the mating surfaces on both exhaust manifolds. Inspect manifolds for cracks, especially around bolt holes and between ports. Check that all bolt holes are clear and threads are clean. Verify heat riser valve moves freely on passenger side manifold.
10. 10

    Install new gaskets and driver side manifold
    Position the new gasket on the driver side cylinder head, aligning all port openings. Some gaskets are self-locating; others may require a small amount of high-temp gasket sealant to hold in place. Carefully position the driver side manifold over the studs and onto the gasket. Start all bolts by hand before tightening any.
11. 11

    Tighten driver side manifold bolts
    Tighten the driver side exhaust manifold bolts in a spiral pattern from the center outward. Typical torque specification for AMC 390 exhaust manifold bolts is 20-25 ft-lbs, though verify with a service manual. Tighten in two stages: first to half torque, then to final torque in the same pattern.
12. 12

    Install passenger side gasket and manifold
    Position the new gasket on the passenger side cylinder head. Install the passenger side manifold with heat riser valve, ensuring the heat riser control arm is properly oriented. Start all bolts by hand, ensuring any brackets are in their correct positions.
13. 13

    Tighten passenger side manifold bolts
    Tighten the passenger side exhaust manifold bolts using the same spiral pattern and torque sequence as the driver side. Verify the heat riser valve linkage has adequate clearance and is not binding.
14. 14

    Reconnect exhaust pipes and accessories
    Install new exhaust pipe flange gaskets if not included in your gasket set. Reconnect both exhaust pipes to their respective manifolds and tighten flange bolts securely. Reinstall heat shields, dipstick tube bracket, choke heat tube, and any other components removed during disassembly. Reconnect spark plug wires if disconnected.

Reassembly

1. Reinstall air cleaner assembly and verify all carburetor linkages operate freely
2. Reconnect negative battery cable
3. Lower vehicle from jack stands

Verification

• Start engine and allow to idle, listening carefully for any exhaust leaks at the manifold gaskets
• With engine at idle, carefully feel around manifold flanges for escaping exhaust gases (do not touch hot surfaces)
• Check for proper operation of heat riser valve on passenger side
• Allow engine to reach operating temperature and re-check for leaks
• After initial heat cycle, allow engine to cool and re-torque all manifold bolts to specification

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