MS9068-009 - Lycoming Rubber Silicone O-Ring

MS9068-009 – Lycoming OEM Fluorosilicone O-Ring Seal

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Overview

The MS9068-009 is a flight-critical, preformed O-ring packing seal, supplied as a genuine Lycoming Engines Original Equipment Manufacturer (OEM) component. It is manufactured in strict accordance with Military Standard MS9068. Crucially, this specification calls for a Fluorosilicone (FVMQ) elastomer, not standard Silicone. Fluorosilicone is specifically engineered to combine the exceptionally wide operating temperature range of silicone, especially its excellent low-temperature flexibility, with enhanced resistance to hydrocarbon fuels, oils, and solvents – properties lacking in basic silicone rubber.

The -009 suffix designates the O-ring's size according to the AS568 dimensional standard. This seal is designed for static applications within Lycoming piston engines, particularly in areas involving fuel or oil systems where components are exposed to significant temperature fluctuations, including extreme cold. As the genuine Lycoming OEM part, it guarantees the precise material compound and dimensions required for a leak-free seal and reliable engine operation.

Key Features

• Genuine Lycoming Engines OEM Part: Guarantees the part is the factory-specified and fully certified component, ensuring correct material performance and airworthiness.

• Fluorosilicone (FVMQ) Compound: Fabricated from a specialized elastomer offering an exceptionally wide temperature range (superior low-temperature performance compared to FKM/Viton®) combined with good resistance to fuels and oils.

• MS9068 Standard Compliance: Guarantees adherence to the military standard for material properties, dimensional tolerances, and quality control specifically for fluorosilicone O-rings.

• AS568 Size -009: Precisely dimensioned according to the AS568-009 standard for a perfect fit in corresponding glands.

• Excellent Low-Temperature Flexibility: Maintains sealing integrity at extremely low temperatures where other elastomers like Fluorocarbon (Viton®) can become brittle.

• Designed for Static Sealing: Provides a reliable seal between two stationary engine components.

Technical Specifications

• Part Number: MS9068-009

• Component Type: Preformed O-Ring Packing Seal

• OEM Authority: Lycoming Engines

• Governing Specification: MS9068

• Material: Fluorosilicone Rubber (FVMQ)

• Hardness: 70 ± 5 Durometer Shore A

• Color (Typical): Blue (often used to identify Fluorosilicone)

• Dimensions (AS568-009):

  • Inside Diameter (ID): 0.208 inches

  • Cross-Section (CS): 0.070 inches

• Typical Temperature Range: -85°F to +400°F (-65°C to +204°C)

• Compatible Fluids: Petroleum-based engine oils, aviation gasoline (Avgas), jet fuels (limited), synthetic lubricants (check specific compatibility).

• Incompatible Fluids: Phosphate ester hydraulic fluids (Skydrol®), ketones, strong acids.

Aircraft Compatibility

As a Lycoming OEM part conforming to MS9068, this O-ring is specified for use in various locations on a wide range of Lycoming piston engines.

• Primary Lycoming Engine Series:

  • O-235, O-320, O-360, IO-360, AEIO-360

  • O-540, IO-540, AEIO-540, TIO-540

  • IO-720

Note: Verification of applicability is the absolute responsibility of the installer. The engine's current Illustrated Parts Catalog (IPC) for the specific engine serial number is the final authority for confirming part number eligibility.

Applications

• Static sealing in fuel system components: fuel injectors, fuel pumps, servo regulators.

• Oil system components: propeller governor mounting pads, accessory case components, oil filter adapters.

• Any engine location requiring a static seal with both fuel/oil resistance and excellent performance across a very wide temperature range, especially cold-start capability.

Why Choose this MS9068-009?

Material selection for engine seals is critical. The MS9068-009 Fluorosilicone O-ring provides a unique balance of properties essential for Lycoming engines. Standard Silicone offers the temperature range but lacks fuel resistance. Standard Fluorocarbon (Viton®) offers fuel resistance but stiffens considerably at very low temperatures. Fluorosilicone bridges this gap. Using the genuine Lycoming OEM part guarantees you are installing the correct, certified FVMQ material specified by the engine manufacturer, preventing leaks caused by material incompatibility or low-temperature failure.

The unique performance profile of the MS9068-009 O-ring is derived from the polymer chemistry of Fluorosilicone (FVMQ). Its molecular structure cleverly combines features of both Silicone (VMQ) and Fluorocarbon (FKM) elastomers. The polymer backbone is primarily composed of repeating silicon-oxygen (-Si-O-) units, identical to standard silicone. This siloxane backbone is responsible for the material's exceptionally low glass transition temperature, granting it flexibility down to -85°F (-65°C) or lower, far exceeding that of FKM. However, unlike standard silicone which has methyl groups attached to the silicon atoms, FVMQ incorporates trifluoropropyl groups (($-CH_2CH_2CF_3$)) along the chain. These fluorine-containing groups impart polarity to the molecule, significantly increasing its resistance to swelling and degradation by non-polar hydrocarbon fuels and oils, similar to how fluorine provides chemical resistance in FKM. This molecular hybridization results in an elastomer uniquely suited for aerospace engine seals that must function reliably from arctic cold starts to high operating temperatures while immersed in fuel or oil.

Note: This component has a finite shelf life defined by standards like ARP5316. The cure date marked on the packaging must be verified prior to installation. It is a single-use part; a new O-ring must be used every time a fitting is reinstalled. Meticulous cleanliness is required during installation. The O-ring must be lubricated only with clean engine oil or an approved compatible lubricant as specified in the engine maintenance manual. Never use incompatible lubricants.

Documentation

The military standard governing this part may be publicly available through the Department of Defense ASSIST database. OEM-specific application and installation data is contained within the Lycoming Engines maintenance and parts manuals.

• ASSIST Document (Reference - Check for MS9068): http://quicksearch.dla.mil/