Intake Manifold

This procedure covers the removal and replacement of the intake manifold on a 1970 AMC Rebel Machine with 390ci V8 engine, including removal of carburetor, distributor, and all associated components.

Warnings

Tools required

Parts

• Intake manifold gasket set × 1 — Use OEM specification for AMC 390
• Intake manifold end seals × 1 — Use OEM specification
• Carburetor base gasket × 1 — Match to carburetor type
• Thermostat housing gasket × 1 — Use OEM specification
• RTV silicone sealant (high-temp) × 1 — Use OEM specification
• Intake manifold bolt set (if replacing) × 1 — Optional replacement

Fluids

• Engine coolant — 4 qt

Preparation

1. Ensure engine is completely cool to the touch (preferably overnight)
2. Disconnect negative battery cable
3. Position drain pan under radiator and drain coolant to below intake manifold level
4. Take photos or make diagrams of all vacuum line routing, especially around carburetor and distributor
5. Label all electrical connections with tape and marker for identification
6. Clean external surfaces of intake manifold and valve covers to prevent debris from entering engine

Procedure

1. 1

   Remove air cleaner and related components
   Remove the air cleaner assembly including the wing nut, housing, and filter element. Disconnect and label the PCV valve breather hose from the air cleaner base. Remove the air cleaner base from the carburetor by removing the mounting studs or bolts. Set aside all components in a clean area.
2. 2

   Disconnect fuel and vacuum lines
   Disconnect the fuel line from the carburetor inlet using appropriate wrenches to avoid stripping the fitting. Have a rag ready to catch residual fuel. Disconnect and label all vacuum lines attached to the carburetor, intake manifold, and distributor vacuum advance. The 390 typically has vacuum lines for distributor advance, PCV system, and potentially transmission modulator if equipped.
3. 3

   Remove carburetor and linkage
   Disconnect the throttle linkage, kickdown linkage (if automatic transmission), and choke linkage from the carburetor. Remove the four carburetor mounting nuts and carefully lift the carburetor straight up off the studs. Plug the intake manifold openings with clean rags to prevent debris entry. Remove and retain carburetor studs if they need to be transferred to new manifold.
4. 4

   Remove distributor
   Mark the position of the distributor body relative to the intake manifold and engine block using a marker or scribe. Note the position of the rotor pointing direction. Remove the distributor cap and set aside with spark plug wires attached. Remove the distributor hold-down bolt and clamp. Carefully pull the distributor straight up out of the engine, noting the rotor will rotate slightly as the drive gear disengages.
5. 5

   Disconnect coolant hoses and temperature sender
   Remove upper radiator hose from the thermostat housing on the intake manifold. Remove heater hoses from intake manifold fittings if present on this casting. Disconnect the coolant temperature sender wire. Be prepared for coolant spillage and have rags or drain pan positioned appropriately.
6. 6

   Remove remaining accessories and brackets
   Remove any remaining brackets, ground straps, or accessories mounted to the intake manifold. This may include coil bracket, alternator brace, air conditioning or emissions components depending on specific equipment. Remove PCV valve from valve cover or intake manifold. Ensure all electrical connections, hoses, and hardware are removed from the manifold.
7. 7

   Remove intake manifold mounting bolts
   Starting from the outside and working toward the center, evenly loosen all intake manifold mounting bolts approximately 2-3 turns each in sequence. Once all are loose, remove the bolts completely and store them in order. The AMC 390 typically uses 12 intake manifold bolts. Check for any hidden bolts beneath the carburetor pad or at the front/rear of the manifold.
8. 8

   Remove intake manifold
   Carefully lift the intake manifold straight up and off the engine. The manifold may be stuck due to old gasket material and sealant. If stuck, gently tap the manifold casting ears with a soft mallet or use a pry point on a casting boss only (never between gasket surfaces). Remove the rags from the intake ports immediately and inspect the valley for any debris or coolant pooling.
9. 9

   Clean all gasket surfaces
   Thoroughly clean all old gasket material from the cylinder head mating surfaces and intake manifold using a gasket scraper. Be careful not to gouge the aluminum intake manifold surface. Use brake cleaner or carburetor cleaner to remove all oil and residue. Stuff clean rags into the intake ports and lifter valley to prevent debris from entering the engine. Use shop vacuum or compressed air to remove all debris. Inspect surfaces for warpage, cracks, or damage. Check cylinder head surfaces are flat and true.
10. 10

    Install new intake manifold end seals
    Apply a small bead of RTV silicone sealant to the front and rear engine block surfaces where the end seals will sit. Install the new rubber intake manifold end seals (front and rear) ensuring they are properly seated in the block valleys. The seals should fit snugly against the block with the lips facing upward. Apply a small amount of RTV at the four corners where the end seals meet the cylinder head gaskets to prevent leaks.
11. 11

    Install intake manifold gaskets
    Position the new intake manifold gaskets on each cylinder head. Most AMC gaskets have alignment tabs or pins to ensure correct positioning. Ensure the port openings align correctly and the gaskets sit flat against the heads. Some gaskets may require a light coating of sealant while others are dry-install; follow gasket manufacturer instructions. Verify all water passages and oil drain-back holes are properly aligned.
12. 12

    Install intake manifold
    Carefully lower the intake manifold into position, aligning it with the gaskets and ensuring it seats evenly on both cylinder heads and the end seals. Do not slide the manifold or disturb the gaskets. Guide the manifold straight down. Insert all manifold bolts finger-tight starting from the center and working outward to hold the manifold in position.
13. 13

    Torque intake manifold bolts to specification
    Tighten the intake manifold bolts in three progressive stages using a crisscross pattern from the center outward. Since torque specifications are not provided in the database, consult a factory service manual for the AMC 390 engine (typical specification is 40-45 ft-lbs, but verify before proceeding). First pass: tighten to 1/3 of final torque. Second pass: tighten to 2/3 of final torque. Third pass: tighten to final specification. Allow manifold to sit for 15-20 minutes, then perform a final torque check.
    ⚠Consult factory service manual for correct torque specification and sequence. Improper torque or sequence will cause vacuum and coolant leaks.
14. 14

    Reinstall distributor and accessories
    Install the distributor by aligning the rotor with the mark made during removal and engaging the drive gear with the camshaft. The rotor will rotate slightly as it drops in. Align the distributor body with the reference mark and install the hold-down clamp and bolt finger-tight (final timing adjustment will be needed). Reinstall all brackets, coolant temperature sender, PCV valve, and any other accessories removed from the manifold.
15. 15

    Install carburetor and reconnect all lines
    Install new carburetor base gasket. If transferring studs to a new manifold, ensure they are properly installed and tight. Mount the carburetor onto the studs and install the mounting nuts, tightening evenly in a crisscross pattern. Reconnect throttle linkage, kickdown linkage, and choke cable. Reconnect all vacuum lines according to labels and photos. Reconnect fuel line to carburetor. Install distributor cap. Reconnect all coolant hoses and tighten clamps securely.

Reassembly

1. Double-check that all vacuum lines are connected according to original routing
2. Verify all electrical connections are secure and properly routed
3. Ensure all coolant hoses are properly clamped and secure
4. Reinstall air cleaner base and air cleaner assembly
5. Reconnect negative battery cable

Verification

• Refill cooling system with proper coolant mixture and bleed air from system
• Check for coolant leaks around intake manifold before starting engine
• Start engine and verify distributor timing is close to specification (final timing adjustment required)
• Allow engine to reach operating temperature while monitoring for leaks
• Check for vacuum leaks by listening for hissing sounds around manifold gasket areas
• Verify idle quality is smooth and throttle response is normal
• After engine reaches full operating temperature, shut off and allow to cool, then re-torque intake manifold bolts to specification
• Road test vehicle and verify proper performance under load

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