Exhaust Gasket - Rear

This procedure covers the replacement of the rear exhaust manifold gaskets on a 1966 Chevrolet Corvette with a 327ci V8 engine, requiring removal of exhaust manifolds from the cylinder heads.

Warnings

Tools required

Parts

• Exhaust manifold gasket set (rear/passenger side) × 1 — Use OEM specification or Fel-Pro MS 90026
• Exhaust manifold bolts (if corroded) × 8 — 3/8"-16 x 1.25" Grade 8
• Exhaust pipe flange gasket × 1 — Use OEM specification
• Exhaust flange nuts (if damaged) × 2 — Use OEM specification

Preparation

1. Ensure engine is completely cold to touch
2. Park vehicle on level, solid surface and apply parking brake
3. Place wheel chocks behind front wheels
4. Disconnect negative battery cable to prevent accidental starter engagement
5. Raise rear of vehicle and support on jack stands under rear axle housing or frame
6. Spray all exhaust manifold bolts and exhaust pipe flange nuts with penetrating oil and allow to soak for 30+ minutes

Procedure

1. 1

   Disconnect exhaust pipe from rear manifold
   Working from underneath the vehicle, locate the exhaust pipe flange connection at the rear exhaust manifold outlet. Remove the 2 flange nuts securing the exhaust pipe to the manifold. Support the exhaust pipe with wire or bungee cord to prevent strain on forward connections. Remove and discard the old flange gasket.
2. 2

   Remove spark plug heat shields (if equipped)
   Some 1966 Corvette 327 engines were equipped with spark plug heat shields on the rear manifold. If present, remove the sheet metal shields by removing their retaining clips or screws. Set aside for reinstallation.
3. 3

   Identify and access manifold mounting bolts
   The rear exhaust manifold is secured to the cylinder head by 8 bolts. Access is challenging due to proximity to steering linkage and frame. Identify all bolt locations before attempting removal. The upper bolts are accessed from the engine bay; lower bolts are best accessed from underneath.
4. 4

   Remove upper manifold bolts
   From the engine bay, remove the 4 upper exhaust manifold bolts using a combination of sockets and wrenches depending on clearance. Work slowly and apply additional penetrating oil if resistance is encountered. If a bolt begins to bind or shows signs of breaking, stop and apply heat with a propane torch, then retry.
   ⚠Do not force seized bolts. Broken bolts require cylinder head removal or extraction, significantly extending repair time.
5. 5

   Remove lower manifold bolts
   Working from underneath the vehicle, remove the 4 lower exhaust manifold bolts. These bolts often experience more corrosion due to road splash and condensation. Use a breaker bar for initial loosening if necessary. Keep bolts organized for inspection.
6. 6

   Remove exhaust manifold
   With all 8 bolts removed, carefully work the exhaust manifold away from the cylinder head. The manifold may be stuck to the head due to gasket material bonding or corrosion. Gently tap with a rubber mallet if necessary, but avoid prying against machined surfaces. Remove the manifold from the vehicle.
7. 7

   Remove old gasket material from cylinder head
   Using a gasket scraper and wire brush, thoroughly clean all old gasket material from the cylinder head exhaust port surfaces. The mating surface must be completely clean and flat for proper sealing. Do not gouge or scratch the machined aluminum surface. Wipe clean with a shop towel.
8. 8

   Clean exhaust manifold mating surface
   Clean the exhaust manifold mating surface using the same process as the cylinder head. Remove all carbon deposits, old gasket material, and corrosion. Inspect the manifold for cracks, particularly around bolt holes and port exits. A cracked manifold must be replaced.
9. 9

   Inspect and prepare fasteners
   Inspect all 8 manifold bolts for thread damage, corrosion, or stretching. Replace any questionable bolts. Clean threads on reusable bolts with a wire brush. Apply a small amount of anti-seize compound to bolt threads, avoiding the first 2 threads to prevent contamination of the cylinder head threads.
10. 10

    Install new exhaust gasket and position manifold
    Position the new exhaust manifold gasket on the cylinder head, aligning all port openings. Some gaskets have locating tabs that fit into notches on the head. Carefully position the exhaust manifold onto the gasket, ensuring proper alignment with all bolt holes. Do not allow the manifold to shift and tear the gasket.
11. 11

    Install and torque manifold bolts
    Install all 8 exhaust manifold bolts finger-tight, starting with the center bolts and working outward. This ensures even gasket compression. Torque all bolts in a center-out pattern to 25 ft-lbs in the first pass, then to final specification of 30 ft-lbs in the second pass. Follow a criss-cross pattern to prevent gasket distortion.
    ℹ️Torque specification of 30 ft-lbs is typical for small block Chevrolet exhaust manifolds of this era. Verify with factory service manual if available.
12. 12

    Reconnect exhaust pipe to manifold
    Install a new exhaust pipe flange gasket between the manifold outlet and the exhaust pipe flange. Position the exhaust pipe and install the 2 flange nuts. Torque flange nuts to 35 ft-lbs in a criss-cross pattern to ensure even gasket compression and prevent exhaust leaks.
13. 13

    Reinstall heat shields and lower vehicle
    If spark plug heat shields were removed, reinstall them now using their original fasteners. Remove jack stands and carefully lower the vehicle to the ground. Reconnect the negative battery cable.

Reassembly

1. Torque all fasteners to specification using the sequences described in each step
2. Ensure exhaust pipe is properly supported and not under strain at the flange connection
3. Double-check that all tools and materials have been removed from the engine bay and undercarriage

Verification

• Start the engine and allow to idle. Listen carefully for exhaust leaks at the manifold-to-head junction and the exhaust pipe flange. A hissing sound indicates a leak.
• With engine at idle, carefully feel around the manifold flange (without touching hot components) for escaping exhaust gas
• Allow engine to reach operating temperature, then shut off and allow to cool. Re-check torque on all manifold bolts after the first heat cycle
• Inspect for any signs of exhaust soot or staining around gasket areas after the first 50-100 miles of driving

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