Exhaust Manifold Studs

This procedure covers the removal and replacement of exhaust manifold studs on the 390ci V8 engine, including extraction of broken studs and proper installation of new fasteners.

Warnings

Tools required

Parts

• Exhaust manifold studs (7/16"-14 or 1/2"-13 depending on location) × 16 — Use OEM specification
• Exhaust manifold gaskets × 2 — Use OEM specification
• Anti-seize compound (high-temperature) × 1 — Use copper or nickel-based
• Helicoil inserts (if threads damaged) × 1 — Size as needed for thread repair
• Exhaust manifold bolts/nuts × 16 — Use OEM specification

Preparation

1. Disconnect negative battery cable
2. Allow engine and exhaust system to cool completely (minimum 2 hours after operation)
3. Raise and support vehicle on jack stands if accessing from below
4. Remove air cleaner assembly and heat riser valve components for better access
5. Apply penetrating oil to all exhaust manifold fasteners and allow to soak for at least 30 minutes (overnight preferred for severely corroded fasteners)
6. Label and disconnect spark plug wires, moving them clear of work area
7. Remove spark plugs to prevent cylinder pressure when rotating engine if needed
8. Disconnect exhaust pipes from manifolds at flange connection

Procedure

1. 1

   Remove exhaust manifolds
   Remove all accessible exhaust manifold nuts or bolts. The 390ci uses 8 studs per manifold. Work from center outward to prevent warping. If fasteners break during removal, mark their locations. Remove manifolds from cylinder heads and set aside on protected surface.
2. 2

   Assess stud condition and plan extraction
   Inspect each stud location. Identify which studs are broken flush, broken below surface, or protruding. For protruding broken studs, attempt removal with locking pliers or stud removal tool first. Document which studs need drilling and extraction.
3. 3

   Remove protruding broken studs
   For studs broken above the surface, clamp with locking pliers or stud removal tool. Apply penetrating oil and allow to soak. Use back-and-forth rotation to break corrosion bond. Apply heat with propane torch if necessary (avoid excessive heat near aluminum components). Remove studs carefully to avoid further breakage.
4. 4

   Center punch broken studs
   For studs broken flush or below surface, use center punch to mark exact center of stud. This is critical for preventing drill bit walkoff. Make a deep, centered indentation. Use a magnifying glass if needed to ensure accuracy. The 390ci cylinder heads are cast iron, allowing some forgiveness, but precision prevents thread damage.
5. 5

   Drill pilot hole in broken stud
   Using a left-hand drill bit (starting with 1/8" size), carefully drill into center of broken stud. Keep drill perpendicular to cylinder head surface. Use slow speed and light pressure. The reverse rotation of left-hand bit may extract stud during drilling. If stud begins to turn, stop drilling and attempt extraction. Drill to depth just short of thread engagement in head.
6. 6

   Progressively enlarge pilot hole
   If stud did not extract with initial drilling, progressively enlarge hole using larger left-hand drill bits. For 7/16" studs, work up to 5/16" bit. For 1/2" studs, work up to 3/8" bit. Leave approximately 1/16" of stud material around threads in cylinder head. Continue using penetrating oil and check frequently for stud movement.
7. 7

   Extract remaining stud material
   Insert appropriate size screw extractor (easy-out) into drilled hole. Tap lightly with hammer to seat extractor. Apply penetrating oil. Turn counterclockwise with wrench or tap handle. Use steady pressure, not impact. If extractor begins to bind or twist, stop immediately and apply more penetrating oil. Heat may be applied to cylinder head around stud (avoid direct heat on extractor). Remove stud remnants completely.
8. 8

   Clean and inspect cylinder head threads
   Once all studs are removed, thoroughly clean each threaded hole with wire brush and compressed air. Remove all carbon deposits, rust, and debris. Inspect threads carefully for damage. Use appropriate tap (7/16"-14 or 1/2"-13) to chase threads and restore proper form. Run tap through each hole completely. If threads are severely damaged or stripped, proceed to thread repair step.
9. 9

   Repair damaged threads if necessary
   For damaged threads that cannot be restored by tapping, install Helicoil or Time-Sert thread repair inserts. Follow kit instructions for proper drill size and tap depth. Ensure insert is installed to correct depth (flush or slightly below surface). Test fit new stud in repaired hole before proceeding. Thread repair is critical for proper manifold clamping force on the 390ci engine.
10. 10

    Clean cylinder head mating surface
    Remove all old gasket material from cylinder head exhaust port surfaces using gasket scraper. Do not gouge or scratch sealing surface. Clean thoroughly with solvent and inspect for cracks or damage. The 390ci exhaust ports run hot and may show heat checking; minor surface imperfections are acceptable if sealing surface is flat.
11. 11

    Install new exhaust manifold studs
    Apply high-temperature anti-seize compound to threads of new studs (bottom 2/3 of threads only, not top section). Install studs into cylinder head by threading two nuts onto stud end and tightening against each other (jam nut method), then turning bottom nut to install stud. Alternatively, use stud installation tool. Install studs to proper depth, typically 3/4 to 1 inch protrusion from head surface. Remove installation nuts. Install all 16 studs (8 per side).
12. 12

    Install exhaust manifold gaskets
    Position new exhaust manifold gaskets on cylinder heads, aligning all port openings. The 390ci uses steel or composite gaskets depending on application. Ensure gaskets are oriented correctly with any alignment tabs or markings facing proper direction. Do not use gasket sealer unless specified by gasket manufacturer.
13. 13

    Install exhaust manifolds
    Carefully position exhaust manifolds onto studs and gaskets. Ensure all studs pass through manifold holes without binding. Install washers and nuts on all studs, threading by hand initially. Start all fasteners before tightening any. Check manifold alignment and ensure gasket has not shifted.
14. 14

    Torque exhaust manifold fasteners
    Tighten exhaust manifold nuts in progressive stages using cross-pattern sequence (start at center, work outward alternating sides). First pass: snug all fasteners finger-tight plus 1/4 turn. Second pass: torque to 15-20 ft-lbs. Third pass: torque to final specification of 30-35 ft-lbs (typical for 390ci, verify with factory service manual). Allow manifolds to cool if heated during installation, then re-torque.

Reassembly

1. Reconnect exhaust pipes to manifold flanges with new gaskets and hardware
2. Reinstall spark plugs and torque to specification
3. Reconnect spark plug wires in correct firing order
4. Reinstall air cleaner assembly and heat riser components
5. Reconnect negative battery cable
6. Lower vehicle from jack stands if raised

Verification

• Start engine and listen for exhaust leaks at manifold-to-head joints; ticking sound indicates leak
• Check for exhaust smoke or vapors escaping from manifold perimeter
• Allow engine to reach operating temperature and re-check all manifold fasteners for proper torque after heat cycle
• Verify no contact between manifolds and adjacent components (spark plug wires, heat shields, etc.)
• Road test vehicle and verify no exhaust odors in cabin and proper engine performance

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