Distributor Cap and Rotor

Replace the distributor cap and rotor on the AMC 390ci V8 engine to restore proper ignition spark distribution and maintain engine performance.

Warnings

Tools required

Parts

• Distributor cap × 1 — AMC V8 points-style distributor cap
• Distributor rotor × 1 — AMC V8 points-style distributor rotor

Preparation

1. Disconnect negative battery cable and secure away from battery post
2. Allow engine to cool completely if recently run
3. Verify replacement cap and rotor match the original parts before starting
4. Locate the distributor at the rear driver's side of the 390ci V8 engine block

Procedure

1. 1

   Mark and document wire positions
   Before removing anything, use wire markers or masking tape to label each spark plug wire with its cylinder number (1-8). Note the wire routing path, especially where wires pass through loom separators. On the AMC 390, cylinder #1 is the front driver's side. The firing order is 1-8-4-3-6-5-7-2 and the distributor rotates clockwise. Mark the position of the #1 wire on the distributor cap for reference.
2. 2

   Remove spark plug wires from cap
   Grasp each spark plug wire boot at the distributor cap (not the wire itself) and twist gently while pulling straight away from the cap. Remove all eight wires, keeping them organized in their firing order. Do not pull on the wire cores as this can damage the internal conductor.
3. 3

   Remove coil wire
   Remove the coil wire from the center tower of the distributor cap by grasping the boot and pulling straight out. This wire connects from the ignition coil mounted on the intake manifold to the distributor.
4. 4

   Release distributor cap hold-downs
   The AMC distributor uses either two spring clips or two screws to secure the cap. If spring clips, use a flathead screwdriver or needle-nose pliers to carefully pry or release each clip. If screws, use a flathead screwdriver to remove both hold-down screws. Keep the hardware in a safe location for reinstallation.
5. 5

   Remove old distributor cap
   Lift the distributor cap straight up and away from the distributor body. Inspect the inside of the old cap for cracks, carbon tracking, burned terminals, or corrosion. Check that all wire terminals are intact and note any damage patterns that might indicate other ignition system problems.
6. 6

   Remove old rotor
   The rotor is held to the distributor shaft by friction fit or a single screw. If screw-mounted, remove the screw with a flathead screwdriver. Pull the rotor straight up off the distributor shaft. Inspect the rotor tip for burning or erosion and check the brass contact spring for proper tension.
7. 7

   Inspect distributor interior
   With the cap and rotor removed, inspect the breaker points (if so equipped), condenser, and distributor cam for excessive wear or pitting. Check the distributor shaft for excessive play. While this procedure doesn't include points replacement, note any obvious issues for future maintenance. Wipe any dirt or debris from the distributor housing with a clean shop rag.
8. 8

   Install new rotor
   Position the new rotor onto the distributor shaft, aligning any locating tabs or flat spots. The rotor only fits one way on AMC distributors. If screw-mounted, install the retaining screw and tighten securely but do not overtighten the small screw. Apply a small amount of dielectric grease to the rotor tip if desired.
9. 9

   Install new distributor cap
   Position the new distributor cap over the distributor body, aligning the cap with the distributor housing tabs. The cap will only fit in one orientation. Press down firmly to seat the cap fully onto the distributor body. Secure with the original spring clips or screws, ensuring both hold-downs are properly engaged.
10. 10

    Reinstall coil wire
    Insert the coil wire into the center tower of the new distributor cap, pushing firmly until the boot seats completely. Apply a small amount of dielectric grease inside the boot before installation to prevent moisture intrusion and improve conductivity.
11. 11

    Reinstall spark plug wires
    Following your original markings and the 1-8-4-3-6-5-7-2 firing order, install each spark plug wire into its correct tower on the distributor cap. Push each wire boot firmly onto the cap tower until it clicks or seats fully. Ensure wires are routed through the original wire looms and separators to prevent contact with hot exhaust manifolds. Verify #1 cylinder wire is in the correct position relative to your reference mark.
12. 12

    Reconnect battery
    Reconnect the negative battery cable to the battery post and tighten securely. Double-check that all spark plug wires are firmly seated at both the distributor cap and spark plugs.

Reassembly

1. Verify all eight spark plug wires plus coil wire are firmly seated in distributor cap towers
2. Confirm distributor cap hold-downs are properly secured
3. Check that wire routing matches original configuration and wires are not contacting exhaust components

Verification

• Start the engine and listen for smooth idle with no misfiring or popping
• Check for visible spark arcing around the distributor cap in darkness if misfiring occurs
• Verify engine responds smoothly to throttle with no hesitation
• Inspect all wire connections at distributor cap one final time after initial run to ensure none have backed out from vibration

More procedures for this vehicle