Remove and replace damaged or broken exhaust manifold studs on the 327ci V8 engine, ensuring proper sealing and secure mounting of exhaust manifolds.

Warnings

Tools required

Parts

• Exhaust manifold studs × 8 — Use OEM specification
• Exhaust manifold gaskets × 2 — Use OEM specification
• Exhaust manifold to head gaskets (if applicable) × 2 — Use OEM specification

Preparation

1. Park vehicle on level surface and allow engine to cool completely (minimum 4 hours after operation).
2. Disconnect negative battery cable to prevent accidental starter engagement.
3. Raise front of vehicle and support securely on jack stands if working on passenger side manifold for better access.
4. Apply penetrating oil to all exhaust manifold bolts and studs and allow to soak for at least 30 minutes before attempting removal.
5. Remove air cleaner assembly and any accessories blocking manifold access.
6. Disconnect spark plug wires from plugs on the side being worked on and label for correct reinstallation.

Procedure

1. 1

   Remove exhaust manifold
   Disconnect exhaust pipe from manifold at flange connection (2 bolts). Remove the exhaust manifold mounting bolts/nuts that are still intact (verify exact count per side against the factory shop manual — commonly more than 4), working from outside to inside. Carefully remove the exhaust manifold from the cylinder head and set aside on protected work surface.
2. 2

   Assess broken stud situation
   Inspect each broken stud location. If stud is protruding above cylinder head surface, attempt removal with locking pliers or stud removal tool. If stud is flush or recessed below surface, it must be drilled out. Count the total number of studs requiring replacement.
3. 3

   Remove protruding studs
   For any studs extending above the head surface, spray with additional penetrating oil. Use a stud removal tool or double-nut method (thread two nuts onto stud, tighten against each other, then turn lower nut counterclockwise). Apply steady pressure without forcing to avoid breaking stud deeper.
4. 4

   Prepare to drill broken studs
   For flush or recessed studs, use center punch to mark exact center of broken stud. Mark should be as centered as possible to avoid drilling into threads. Clean area around stud with wire brush to ensure good visibility and remove carbon buildup.
5. 5

   Drill pilot hole
   Using a small pilot drill bit (approximately 1/8"), carefully drill a centered pilot hole into the broken stud to depth of approximately 1/2 inch. Keep drill perfectly perpendicular to head surface. Use slow speed and light pressure to maintain control and accuracy.
   ⚠If drill bit wanders off center, stop immediately and reassess. Drilling into threads will require thread repair inserts.
6. 6

   Extract stud with left-hand drill bit
   Install left-hand drill bit sized appropriately for the stud (smaller than the stud's tap-drill size so head threads are not damaged). Drill counterclockwise at low-to-moderate speed. The reverse rotation often grabs and extracts the stud. If stud does not extract, drill to depth where extractor can be used.
7. 7

   Use screw extractor if needed
   If left-hand bit does not extract stud, select proper size screw extractor for the hole drilled. Tap extractor firmly into hole with hammer. Using a wrench or tap handle, turn extractor counterclockwise with steady pressure. Once stud breaks loose, continue turning until completely removed.
   ⚠️Screw extractors are hardened and brittle. Excessive force can break extractor off in hole, creating a much more difficult situation.
8. 8

   Clean and chase threads
   Once all broken studs are removed, thoroughly clean each threaded hole with brake cleaner and compressed air. Run appropriate tap through each hole to clean and restore threads (verify exact stud thread size against the 1966 Corvette factory shop manual before tapping — do not assume). Use thread chaser if threads are in good condition.
9. 9

   Install new studs
   Apply anti-seize compound to lower 2/3 of each stud thread that will thread into cylinder head. Thread stud into head by hand using double-nut method or stud installer tool. Tighten to snug fit plus 1/4 turn. All studs should be installed to same depth with equal thread engagement.
10. 10

    Prepare manifold mating surfaces
    Clean cylinder head exhaust port surfaces thoroughly with gasket scraper and wire brush. Remove all old gasket material and carbon deposits. Clean exhaust manifold mating surface in same manner. Both surfaces must be completely clean and flat for proper sealing.
11. 11

    Install new gaskets
    Position new exhaust manifold gaskets on cylinder head studs, ensuring proper orientation with port alignment. Some gaskets have specific top/bottom orientation. Verify gasket ports align perfectly with head exhaust ports.
12. 12

    Install exhaust manifold
    Carefully position exhaust manifold onto studs and align with gasket and exhaust ports. Start all manifold nuts by hand (verify exact count against the factory shop manual) to ensure proper thread engagement. Do not tighten any nuts until all are started to prevent cross-threading or manifold misalignment.
13. 13

    Torque manifold nuts
    Tighten manifold nuts in sequence from center outward, working in gradual stages. First pass: snug all nuts finger-tight plus 1/4 turn. Second pass: torque to 50% of final specification. Third pass: torque to final specification per the 1966 Corvette factory shop manual (verify exact value; do not assume 25-30 ft-lbs). This prevents warping and ensures even clamping force.
14. 14

    Reconnect exhaust system
    Install new exhaust flange gasket between manifold outlet and exhaust pipe. Connect exhaust pipe to manifold flange and install 2 flange bolts. Tighten flange fasteners in a cross pattern to the value specified in the 1966 Corvette factory shop manual (verify exact value) to ensure even sealing.

Reassembly

1. Reinstall any accessories or brackets removed for manifold access.
2. Reconnect spark plug wires to correct cylinders according to labeling.
3. Reinstall air cleaner assembly and verify all vacuum lines are connected.
4. Reconnect negative battery cable.
5. Lower vehicle from jack stands if raised.

Verification

• Start engine and listen for exhaust leaks at manifold-to-head and manifold-to-pipe connections.
• Allow engine to reach operating temperature and recheck for leaks under load.
• After initial heat cycle, recheck manifold nut torque when engine is cool (recommended after 50-100 miles).
• Verify no unusual exhaust smell in engine compartment indicating exhaust leak.

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