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MS29513-034 – Aerospace High-Temperature Fuel & Oil O-Ring
Available now through the AirParts Aero marketplace.
Overview Section
The MS29513-034 is a specialized, fuel-resistant Aviation O-Ring engineered for high-performance aircraft engine and airframe applications. Manufactured to the Military Standard (MS) 29513, this O-ring is specifically designed for environments characterized by constant exposure to petroleum-based fluids and wide temperature fluctuations.
The -034 dash size features a large 2.114-inch Inside Diameter paired with a very slim 1/16-inch (0.070") cross-section. This "low-profile" geometry is ideal for large-diameter sealing surfaces with tight clearance requirements, such as accessory mounting pads, large fuel line couplings, and engine inspection covers.
Key Features Section
Fuel & Aromatic Resistance: Optimized with a high-nitrile (Buna-N) content to resist swelling and degradation when exposed to 100LL Avgas, Jet-A, and mineral-based engine oils.
Engine Compartment Stability: Maintains its elastic sealing "memory" in temperatures ranging from -40°F to +250°F.
Precision AS568-034 Sizing: Manufactured to strict aerospace tolerances, ensuring a predictable "squeeze" and volume fill in standard narrow-gland applications.
Low Compression Set: Engineered to resist permanent "flattening," ensuring a persistent seal even during long periods of aircraft storage or engine inactivity.
70 Durometer (Shore A): Provides the standard medium hardness required to seal effectively against irregular metal surfaces while resisting extrusion under moderate pressures.
Certified Performance: Meets all MS29513 requirements for tensile strength and elongation, ensuring compliance with FAA-certified engine data sheets.
Technical Specifications Section
| Specification | Detail |
| Standard | MS29513 (Supersedes AN6227 series) |
| Dash Size | -034 |
| Material | Acrylonitrile Butadiene (Nitrile / Buna-N) |
| Inside Diameter (ID) | 2.114 in (53.70 mm) |
| Outside Diameter (OD) | 2.254 in (57.25 mm) |
| Cross-Section (W) | 0.070 in (1.78 mm) |
| Hardness | 70 Shore A |
| Color | Black |
Aircraft Compatibility Section
The MS29513-034 is found in several high-criticality areas across general aviation and turbine fleets:
Lycoming & Continental Engines: Used for sealing large-diameter accessory mounting pads and specialized oil scavenge pump interfaces.
Fuel Systems: Often found in the main seals for large-bore fuel selector valves and specialized fuel tank access ports.
Hydraulic Components: Utilized in low-pressure return line manifolds and reservoir caps where fuel/oil resistance is mandatory.
Environmental Control Systems (ECS): Found in large-diameter air-oil heat exchanger couplings.
Technical Applications & Safety
In aerospace glands, the O-ring creates a seal by being deformed between two mating surfaces. Because the MS29513-034 has a very thin 1/16-inch thickness relative to its large diameter, it is particularly susceptible to "spiraling" during installation if not properly handled.
Safety Warning: Do not substitute with standard industrial Nitrile. While an industrial O-ring may share the -034 dimensions, the elastomer chemistry is not certified for aviation fuel and can leach plasticizers, causing the seal to shrink and fail. Always verify the Cure Date on the packaging; Nitrile O-rings generally have a 15-year shelf life. Expired seals may appear fine but can crack when subjected to the high-frequency vibrations of a running engine.
Technical Engineering Insight
The engineering value of the MS29513-034 lies in its Surface-to-Volume Ratio. Because this O-ring is very thin (0.070"), it has a high surface area relative to its mass, allowing it to react quickly to thermal changes in the engine case. This is vital for maintaining a seal during the "warm-up" phase of an engine when the aluminum housing expands faster than the steel mounting bolts. However, this thinness means that the Gland Depth must be machined to extremely high tolerances; even a 0.005" error in machining can result in a total lack of compression, leading to chronic "weeping" of fuel or oil.
Installation & Maintenance Addendum
Avoid Spiral Failure: Because of the large ID and thin cross-section, the -034 can easily twist. Always use Parker O-Lube or clean system fluid during assembly to ensure the ring "slides" rather than "rolls."
Tooling Safety: Only use brass or plastic O-ring picks. A single scratch in a gland intended for a 1/16" O-ring will create a leak path that is nearly impossible to stop without resurfacing the part.
Visual Inspection: Before final torque, ensure the O-ring hasn't "popped out" of the groove. With large-diameter, thin rings, they can occasionally expand slightly out of the gland during handling.
