MS29513-238 - Military Standards Oil Filter Housing O-Ring

MS29513-238 – Nitrile (Buna-N) Oil Filter Housing O-Ring

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The MS29513-238 is a flight-critical, preformed O-ring packing manufactured in strict accordance with Military Standard MS29513. This large-diameter seal is most commonly specified as the primary O-ring for the engine oil filter housing or adapter plate on a vast number of general aviation aircraft. Its sole function is to create a positive, leak-free seal that contains the full pressure of the engine's lubrication system. The integrity of this single O-ring is directly responsible for retaining the engine's entire supply of lubricating oil.

This O-ring is fabricated from a 75 durometer Nitrile (Buna-N) synthetic rubber compound, the industry-standard material for sealing petroleum-based fluids. The MS29513 specification guarantees that the O-ring meets the stringent requirements for material composition, dimensional tolerance, and quality control demanded for certified aircraft. A failure of this seal in flight would be catastrophic, leading to a rapid and total loss of engine oil and certain engine seizure.

Key Features

• Military Standard (MS) Certified: Manufactured to the exact material, hardness, and dimensional tolerances of the MS29513 specification, ensuring reliable sealing performance.

• Nitrile (Buna-N) 75 Durometer Material: The specified elastomer provides excellent resistance to petroleum-based engine oils, greases, and aviation gasoline.

• Contains High-Pressure Engine Oil: Engineered to withstand the full pressure and temperature of a piston engine's lubrication system without leaking, swelling, or degrading.

• Excellent Compression Set Resistance: Made from a compound that resists permanent deformation ("flattening") after being compressed for long periods, ensuring a reliable seal between oil changes.

• Mandatory Single-Use Component: A flight-critical seal that must be replaced every time the oil filter is serviced to guarantee the integrity of the oil system.

Technical Specifications

• Part Number: MS29513-238

• Component Type: Preformed Packing, O-Ring

• Governing Specification: MS29513

• Material: Nitrile Rubber (Buna-N / NBR).

• Hardness: 75 Durometer Shore A.

• Size (AS568A Dash Number): -238

• Dimensions:

  • Inside Diameter: 3.609 inches (91.67 mm)

  • Cross-Section: 0.139 inches (3.53 mm)

Aircraft Compatibility

The MS29513-238 is a standard hardware component used on many aircraft, particularly as the oil filter adapter or housing seal on a vast range of Textron Aviation (Cessna) single-engine and light-twin aircraft, among others.

Crucial Note: The correct part number for a specific aircraft and engine combination must be verified against the latest revision of the aircraft's Illustrated Parts Catalog (IPC) or maintenance manual.

Applications

• Primary Application: Creating a positive seal between the engine oil filter adapter/housing and the engine accessory case.

• Mandatory Replacement at every oil filter change or any time the oil filter housing is removed from the engine.

Why Choose MS29513-238?

Choosing a genuine MS29513-238 O-ring is a non-negotiable decision for flight safety. The failure of the oil filter housing seal will result in the rapid, high-pressure evacuation of the engine's entire oil supply, leading to catastrophic engine failure in-flight. Re-using an old, flattened, or heat-hardened O-ring is a guarantee of a future leak. Using a non-certified O-ring from an industrial source risks incorrect material composition that is not compatible with aviation engine oil, or incorrect dimensions leading to an improper seal. The MS standard guarantees the certified material and quality required for this zero-failure-tolerance application.

A critical property for the MS29513-238, beyond its basic fluid compatibility, is its specified low compression set. Compression set is the permanent deformation an elastomer exhibits after being subjected to a prolonged compressive stress at a given temperature. An O-ring seals by being compressed ("squeezed") in its groove, where it "pushes back" against the mating surfaces. The MS29513 standard mandates a Nitrile compound with a low compression set value, ensuring it retains a high percentage of this "push back" force over time. This is vital for the oil filter housing application, where the O-ring is compressed continuously for the entire 50-hour (or longer) interval between oil changes, all while being subjected to high engine temperatures. An elastomer with poor compression set resistance would permanently flatten, losing its elastic memory. This would result in a loss of sealing force, especially during the thermal cycles of engine startup and shutdown, creating a leak path for high-pressure oil and leading to a potentially catastrophic failure.

Note: This is a flight-critical, single-use component. This O-ring MUST be replaced with a new one every time the oil filter housing is opened or the filter is changed. Re-using this O-ring will lead to a catastrophic engine oil leak. Before installation, ensure the O-ring and both sealing surfaces are perfectly clean and free of debris. The new O-ring should be lightly lubricated with clean engine oil prior to assembly. Installation must be performed by a certified A&P mechanic.

Documentation

The definitive technical requirements for this component are detailed in Military Standard MS29513. Applicability must be confirmed via the aircraft's Illustrated Parts Catalog (IPC).