Remove and replace all eight spark plugs on the 1966 Chevrolet Corvette 327ci V8 engine, including inspection of plug wires and proper gapping of new plugs.

Warnings

Tools required

Parts

• Spark plugs (resistor type) × 8 — AC Delco R44 or equivalent, gapped to 0.035"

Preparation

1. Ensure engine is completely cool to the touch
2. Park vehicle on level surface and engage parking brake
3. Open hood and secure with prop rod
4. Verify you have correct spark plug type and gap specification (0.035" for 327ci V8)
5. Organize workspace to keep plug wires in firing order sequence during removal

Procedure

1. 1

   Label and document spark plug wire routing
   Before removing any wires, note the firing order (1-8-4-3-6-5-7-2) which should be marked on the intake manifold. The cylinders are numbered 1-3-5-7 on the driver side (front to rear) and 2-4-6-8 on the passenger side (front to rear). If desired, use masking tape to label each wire with its cylinder number to ensure correct reinstallation.
2. 2

   Remove spark plug wire from cylinder #1
   Grasp the spark plug wire boot firmly at the base where it connects to the spark plug on the driver side front cylinder. Twist the boot slightly while pulling straight away from the plug to break the seal. Never pull on the wire itself as this can separate the conductor from the terminal. Set the wire aside in a clean area.
3. 3

   Clean spark plug well area
   Use compressed air or a shop vacuum to clean any dirt, debris, or oil from around the exposed spark plug before removal. This prevents contaminants from falling into the cylinder when the plug is removed.
4. 4

   Remove spark plug from cylinder #1
   Install the 13/16" spark plug socket with extension onto the spark plug. Turn counterclockwise to loosen and remove the plug completely. Inspect the removed plug for abnormal wear, fouling, or deposits which can indicate engine problems. Set the old plug aside for comparison with others.
5. 5

   Inspect cylinder #1 plug hole threads
   Visually inspect the spark plug hole threads in the cylinder head for damage, carbon buildup, or stripped threads. If threads show carbon buildup, use a wire brush or thread chaser to clean them. Do not allow debris to fall into the cylinder.
6. 6

   Prepare and gap new spark plug for cylinder #1
   Remove a new spark plug from its package. Use the spark plug gap tool to verify the gap is set to 0.035". Adjust if necessary by carefully bending the ground electrode. Anti-seize is generally not required on the cast-iron heads of this engine, but if used apply only a very small amount to the threads (avoid getting any on the electrode or insulator) and reduce torque slightly. Do not apply anti-seize if plugs come pre-treated.
7. 7

   Install new spark plug in cylinder #1
   Thread the new spark plug into the cylinder head by hand, turning clockwise. This ensures the plug is not cross-threaded. Once hand-tight, use the spark plug socket and ratchet to snug the plug. Tighten to approximately 25 ft-lbs (1/4 turn past hand-tight for new plugs with gaskets). The plug should be firmly seated but not over-torqued.
8. 8

   Reinstall spark plug wire to cylinder #1
   Apply a small amount of dielectric grease inside the spark plug wire boot if available. Push the boot firmly onto the spark plug until you feel and hear it click into place over the plug terminal. Ensure the boot is fully seated to prevent misfires.
9. 9

   Repeat process for remaining cylinders
   Working one cylinder at a time, repeat steps 2 through 8 for the remaining seven cylinders in any convenient order. Complete one cylinder fully before moving to the next to avoid mixing up plug wires. On the passenger side, access may be more restricted due to exhaust manifold proximity; use caution to avoid contact with hot or sharp edges.
10. 10

    Inspect all spark plug wires
    With all new plugs installed and wires reconnected, visually inspect each spark plug wire for cracks, burns, or damage to the insulation. Check that all boots are fully seated on both the spark plug and distributor cap ends. Ensure wires are routed away from exhaust manifolds and are not pinched or kinked.

Reassembly

1. Double-check that all eight spark plug wires are connected to the correct cylinders per firing order 1-8-4-3-6-5-7-2
2. Verify all plug wire boots are fully seated on plugs and distributor cap
3. Ensure no tools or shop towels are left in engine compartment

Verification

• Start the engine and listen for smooth idle with no misfires or unusual sounds
• Engine should start more easily and idle smoother than before if old plugs were worn
• Check for arcing or sparking around plug wires in darkness or low light conditions
• No Check Engine light or rough running should be present
• Take a brief test drive to confirm smooth acceleration and no hesitation under load

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