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MS29513-114 – Aircraft Engine High-Temperature O-Ring
Available now through the AirParts Aero marketplace.
Overview Section
The MS29513-114 is a specialized, fuel-resistant Aviation O-Ring specifically designed for aircraft engine applications.1 Manufactured to the Military Standard (MS) 29513, this O-ring is engineered to provide a high-integrity seal in environments characterized by high temperatures and constant exposure to petroleum-based fluids.
While it shares dimensions with standard industrial O-rings, the MS29513 series is distinguished by its material chemistry—a medium-to-high nitrile (Buna-N) compound specifically optimized for fuel system service. It is the primary choice for sealing interfaces in carburetors, fuel injection systems, and oil lines where failure-free performance is a flight-safety requirement.
Key Features Section
Fuel & Oil Optimization: Specifically formulated to resist swelling and degradation when in constant contact with 100LL Avgas, Jet-A, and mineral-based engine oils.
High-Heat Tolerance: Capable of maintaining its sealing "memory" in engine compartment temperatures ranging from -40°F to +250°F.
Precision -114 Sizing: Manufactured to the AS568 standard dash size -114, ensuring a perfect "void-to-volume" fill in standard aerospace glands.
Low Compression Set: Engineered to resist "flattening" over time, ensuring a persistent seal against mating surfaces even during long periods of engine inactivity.
70 Durometer (Shore A): Provides the ideal medium hardness to seal irregular surfaces while remaining stiff enough to resist extrusion under moderate pressures.
MS-Certified Reliability: Meets the strict quality control standards for tensile strength and elongation required for FAA-certified engines.
Technical Specifications Section
| Specification | Detail |
| Standard | MS29513 (Supersedes AN6227 series) |
| Dash Size | -114 |
| Material | Acrylonitrile Butadiene (Nitrile / Buna-N) |
| Inside Diameter (ID) | 0.612 in (15.54 mm) |
| Outside Diameter (OD) | 0.812 in (20.62 mm) |
| Cross-Section (W) | 0.103 in (2.62 mm) |
| Hardness | 70 Shore A |
| Color | Black |
Aircraft Compatibility Section
The MS29513-114 is a critical seal for both legacy and modern reciprocating engines:
Lycoming & Continental Engines: Frequently used in oil cooler bypass valves, fuel injector manifolds, and pushrod housing seals.
Precision Airmotive (Bendix) Carburetors: Found in the fuel inlet fittings and mixture control shafts of the MA-series carburetors.
Cessna & Piper Fuel Systems: Used in fuel selector valves and fuel strainer (gascolator) assemblies.
General Aviation Accessories: Often utilized in engine-driven vacuum pumps and oil temperature bulb adapters.
Technical Applications & Safety
In aircraft engines, the MS29513-114 creates a seal by being "squeezed" between two metal surfaces. Because engine vibration is constant, the O-ring must maintain its elasticity to prevent "weeping."
Safety Warning: Do not substitute with standard industrial Nitrile O-rings. While a hardware-store O-ring may share the -114 dimensions, its rubber compound is not certified for high-octane aviation fuel. It may swell or dissolve, leading to fuel leaks or engine-stoppage due to debris in the fuel lines. Additionally, check the Cure Date (shelf life) on the packaging; Nitrile O-rings typically have a 15-year shelf life.3 Expired seals become brittle and can crack upon installation.4
Avoid Spiral Failure: When installing the O-ring over a long shaft, use a small amount of clean engine oil or Parker O-Lube to ensure it slides without twisting.
Tooling: Use a plastic O-ring pick to remove the old seal. Scratches on the aluminum gland caused by metal screwdrivers are a primary cause of persistent leaks.
Visual Check: Ensure the O-ring is seated flat in the groove before tightening the mating part. A "pinched" O-ring will fail immediately upon the application of fuel pressure.
