77611 - Lycoming OEM Exhaust Flange Gasket

77611 – Lycoming OEM Exhaust Flange Gasket

Part Number: 77611

Manufacturer: Lycoming Engines (A Textron Company)

Standard Series: High-Temperature Exhaust Hardware

Common Synonyms: Exhaust Port Gasket, "No-Leak" Flange Gasket, 77611 Metal/Graphite Gasket

Overview Section

The 77611 is a genuine Lycoming OEM high-temperature exhaust flange gasket, engineered to provide a gas-tight seal between the cylinder exhaust port and the exhaust riser (header). It is the modern, "heavy-duty" replacement for older copper or asbestos-style gaskets and is compatible with nearly all parallel-head and angle-head Lycoming engines, including the O-320, O-360, and IO-540 series.

Constructed from a composite of stainless steel and high-density graphite (or specialized spiral-wound material in some variants), the 77611 is designed to expand and contract with the extreme thermal cycles of a piston engine. This prevents "exhaust blow-by," which can lead to cylinder head erosion, power loss, and the dangerous accumulation of carbon monoxide within the aircraft cowling.

Enhanced Technical Data

Advanced Engineering & Structural Application

The 77611 is engineered for Thermal Compliance and Erosion Prevention. Exhaust gas temperatures (EGT) at the port can reach 1,500°F, creating a highly corrosive and abrasive environment.

Engineering Insight: The "Spiral-Wound" Advantage

Modern Lycoming 77611 gaskets often utilize a multi-layer composite design. The stainless steel core provides structural "spring back," ensuring that as the aluminum cylinder head and steel exhaust flange expand at different rates (thermal mismatch), the gasket maintains a constant clamping pressure. The graphite facing acts as a high-temperature lubricant and sealant, filling microscopic imperfections in the flange surfaces to prevent high-velocity gas "jetting" that can permanently scar the cylinder exhaust face.

Carbon Monoxide Safety

The integrity of the 77611 gasket is critical for cabin safety. A failed exhaust gasket allows raw exhaust to leak into the engine nacelle, where it can be drawn into the cabin heater shroud, potentially leading to carbon monoxide poisoning.

Engine Compatibility

The 77611 is the standard exhaust gasket for the majority of the Lycoming fleet:

• Lycoming O-320 & O-360: Found on Cessna 172, Piper Cherokee, and Grumman Tiger.

• Lycoming O-540 & IO-540: Standard for Cessna 182, Piper Saratoga, and various high-performance homebuilts.

• Lycoming O-235: Used in Cessna 152 and Piper Tomahawk trainer aircraft.

• Rotary & Turbocharged Engines: Compatible with TIO-540 and IO-720 series applications.

The Lycoming 77611 is the definitive solution for eliminating exhaust leaks in your piston engine. When performing a cylinder swap or exhaust system maintenance, utilizing genuine 77611 gaskets is the only way to ensure an airworthy, high-temperature seal. These gaskets are engineered to handle the intense vibrations and thermal loads of an aircraft engine, providing a superior life cycle compared to aftermarket copper alternatives. By choosing Lycoming OEM 77611 hardware, you protect your cylinder heads from expensive erosion damage and ensure your cabin heat remains free of hazardous exhaust fumes.

Installation & Maintenance Addendum

1. Flange Flatness: Before installation, check the exhaust riser flange for warping using a straight-edge. If the flange is "bowed," the 77611 will not be able to compensate for the gap, and the gasket will likely blow out.

2. Nut Torque & Retorque: Always use new LW-25-S0.62 high-temp nuts. Exhaust hardware should be retorqued after the first 5–10 hours of operation following a gasket replacement, as the 77611 will undergo a "set" after the first heat cycle.

3. Orientation: The 77611 is generally bi-directional; however, always ensure the port holes are perfectly centered during the tightening process to avoid restricting exhaust flow