Exhaust Manifold

This procedure covers the removal and replacement of the exhaust manifolds on the 1970 AMC Rebel Machine 390ci V8 engine, including all necessary disconnections and reassembly.

Warnings

Tools required

Parts

• Exhaust manifold gasket set × 1 — Use OEM specification
• Exhaust manifold bolts (if corroded) × 1 — Use OEM specification
• Exhaust pipe flange gaskets × 2 — Use OEM specification
• Exhaust flange nuts × 6 — Use OEM specification
• Anti-seize compound × 1 — High temperature rated

Preparation

1. Park vehicle on level ground and allow engine and exhaust to cool completely (minimum 4 hours)
2. Disconnect negative battery cable
3. Raise and safely support front of vehicle on jack stands
4. Apply penetrating oil to all exhaust manifold bolts and exhaust pipe flange nuts, allowing to soak while performing other steps
5. Remove air cleaner assembly and set aside

Procedure

1. 1

   Disconnect exhaust pipes from manifolds
   Working from underneath the vehicle, remove the three nuts securing each exhaust pipe to the exhaust manifold flanges. Support the exhaust pipes to prevent strain on the system. Separate the exhaust pipes from the manifolds and inspect flange condition.
2. 2

   Remove spark plug heat shields (if equipped)
   Remove any heat shields protecting the spark plug wires from exhaust manifold heat. These are typically held by small brackets or clips on the valve covers.
3. 3

   Disconnect spark plug wires from driver side cylinders
   For left manifold removal, disconnect spark plug wires from cylinders 1, 3, 5, and 7. Label wires if necessary. Route wires away from manifold work area to prevent damage during removal.
4. 4

   Remove driver side exhaust manifold
   Remove the eight bolts securing the left exhaust manifold to the cylinder head. Work from the center bolts outward to reduce warping stress. The manifold will be heavy; support it as you remove the final bolts. Carefully lift manifold away from cylinder head, noting any studs that may remain in the head.
5. 5

   Disconnect spark plug wires from passenger side cylinders
   For right manifold removal, disconnect spark plug wires from cylinders 2, 4, 6, and 8. Label wires if necessary. Route wires away from manifold work area.
6. 6

   Remove air injection tube connections (if equipped)
   If vehicle is equipped with air injection system, disconnect the air injection tubes from the exhaust manifold. These are typically secured with compression fittings that may require penetrating oil to loosen.
7. 7

   Remove passenger side exhaust manifold
   Remove the eight bolts securing the right exhaust manifold to the cylinder head. Work from the center bolts outward. Access to some bolts may be restricted by chassis components; use universal joint adapters and extensions as needed. Support manifold weight during removal and carefully lift away from cylinder head.
8. 8

   Clean cylinder head mating surfaces
   Using a gasket scraper and wire brush, thoroughly clean all old gasket material from the cylinder head exhaust port surfaces. Ensure surfaces are completely flat and free of any debris, carbon buildup, or old gasket material. Inspect for cracks or damage to the head surface.
9. 9

   Inspect and prepare manifolds
   Inspect removed manifolds for cracks, warping, or damage. Check mating surfaces with a straightedge; warpage beyond 0.010" requires manifold resurfacing or replacement. Clean manifold mating surfaces thoroughly. Wire brush all bolt holes in cylinder head to ensure proper thread engagement.
10. 10

    Install new gaskets and position passenger side manifold
    Place new exhaust manifold gasket on cylinder head, aligning all ports carefully. Position passenger side manifold onto studs or into position. Start all eight mounting bolts by hand to ensure proper thread engagement before tightening any bolt.
11. 11

    Torque passenger side manifold bolts
    Tighten exhaust manifold bolts in a spiral pattern from center outward. Typical torque specification for AMC 390 exhaust manifold bolts is 40-45 ft-lbs, but verify with factory specifications. Apply light coat of anti-seize to bolt threads before installation. Make two passes: first to 20 ft-lbs, then final torque to specification.
12. 12

    Install driver side manifold and gasket
    Place new exhaust manifold gasket on cylinder head, aligning all ports. Position driver side manifold and start all eight mounting bolts by hand. Torque bolts using same spiral pattern and sequence as passenger side, working from center outward in two passes to final specification.
13. 13

    Reconnect exhaust pipes to manifolds
    Install new exhaust flange gaskets between manifolds and exhaust pipes. Position exhaust pipes to manifold flanges and install new flange nuts. Torque flange nuts evenly in a crisscross pattern to 35-40 ft-lbs to prevent flange warping and ensure leak-free seal.

Reassembly

1. Reconnect all spark plug wires to their respective cylinders in correct firing order (1-8-4-3-6-5-7-2)
2. Reconnect air injection tubes if equipped, ensuring proper sealing
3. Reinstall heat shields and any other components removed for access
4. Reinstall air cleaner assembly
5. Reconnect negative battery cable
6. Lower vehicle from jack stands

Verification

• Start engine and allow to reach operating temperature while monitoring for exhaust leaks at manifold-to-head and manifold-to-pipe connections
• Listen for any ticking or hissing sounds that would indicate exhaust leaks
• Visually inspect all connections for signs of exhaust gas escape (soot marks)
• After initial heat cycle, allow engine to cool and re-torque all manifold bolts to specification
• Verify all spark plug wires are properly routed and secured away from hot exhaust components

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