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MS29513-211 – Aircraft Engine Fuel & Oil Resistant O-Ring
Available now through the AirParts Aero marketplace.
Overview Section
The MS29513-211 is a high-performance Aviation O-Ring specifically designed for use in aircraft engine fuel and lubrication systems. Manufactured from a medium-to-high Nitrile (Buna-N) compound, this O-ring is engineered to withstand the chemically aggressive environment of high-octane aviation gasoline and synthetic engine oils.
The MS29513 series is the primary standard for reciprocating engine seals, particularly where components are subject to significant thermal cycling and vibration. As a -211 dash size, it features a robust 1/8-inch cross-section, providing a substantial sealing surface for larger fluid ports, filter housings, and engine accessory drive interfaces.
Key Features Section
Aromatic Hydrocarbon Resistance: Formulated to resist swelling and degradation when in constant contact with 100LL Avgas and Jet-A fuels.
Engine Compartment Durability: Maintains its sealing properties and elasticity in temperatures ranging from -40°F to +250°F.
Precision -211 Sizing: Manufactured to the AS568 standard dash size -211, ensuring a consistent and reliable "squeeze" in standard aerospace glands.
Vibration Dampening: The thicker 0.139-inch cross-section helps absorb mechanical harmonics between engine components, preventing "weeping" leaks.
Low Compression Set: Engineered to resist permanent flattening, ensuring the seal remains effective during long periods of engine inactivity.
Certified Traceability: Meets all Military Standard (MS) requirements for tensile strength, elongation, and material purity required for flight-certified hardware.
Technical Specifications Section
| Specification | Detail |
| Standard | MS29513 (Supersedes AN6227 series) |
| Dash Size | -211 |
| Material | Acrylonitrile Butadiene (Nitrile / Buna-N) |
| Inside Diameter (ID) | 0.796 in (20.22 mm) |
| Outside Diameter (OD) | 1.074 in (27.28 mm) |
| Cross-Section (W) | 0.139 in (3.53 mm) |
| Hardness | 70 Shore A |
| Color | Black |
Aircraft Compatibility Section
The MS29513-211 is a foundational seal for a variety of aircraft systems:
Lycoming & Continental Engines: Frequently used in oil filter adapter housings, oil cooler fittings, and large-diameter fuel injection manifolds.
Radial Engines: Found in pushrod housing seals and accessory drive mounting pads for Pratt & Whitney and Curtiss-Wright powerplants.
Fuel Systems: Standard seal for larger gascolator (fuel strainer) bowls and main fuel selector valve ports.
Hydraulic Systems: Used in low-pressure return lines and reservoir caps where fuel/oil resistance is required.
Technical Applications & Safety
The MS29513-211 creates a seal through mechanical deformation within a "gland." Because of its 1/8-inch thickness, it is particularly effective at sealing surfaces that may have slight thermal expansion variances.
Safety Warning: Do not substitute with industrial-grade O-rings. While a standard Nitrile O-ring from a hardware store may share the -211 dimensions, the elastomer is not certified for aviation fuel. Standard Nitrile can leach plasticizers into the fuel system, causing the O-ring to shrink, crack, and fail prematurely. Additionally, always verify the Cure Date (shelf life). MS29513 seals typically have a 15-year shelf life; an expired O-ring may feel soft but can fail instantly under the pressure spikes of an engine-driven pump.
Technical Engineering Insight
The engineering value of the MS29513-211 lies in its Volumetric Fill and Gland Design compatibility. Aerospace engineering manuals (such as MIL-HDBK-695) specify that the O-ring should occupy approximately 70–90% of the gland's volume. The -211 size, with its specific 0.139-inch cross-section, is optimized to allow for the thermal expansion of Nitrile without over-filling the groove. If an O-ring fills 100% of the groove during operation, it can act as a solid and crack the aluminum housing or shear the mounting bolts. Sourcing a genuine MS-standard part ensures the volumetric expansion coefficients remain within the engine manufacturer's safety limits.
Installation & Maintenance Addendum
Gland Preparation: Ensure the mounting groove is free of carbon deposits or old "baked-on" rubber. Use only a plastic or brass pick for cleaning to avoid scratching the seating surface.
Lubrication: Lightly coat the O-ring with clean engine oil or Parker O-Lube before installation. This prevents "spiral failure," where the O-ring twists during the assembly of a threaded housing.
Stretch Limits: Avoid stretching the O-ring more than 50% of its diameter during installation, as this can lead to microscopic surface tearing in the Nitrile compound.
