MS29512-06 – Four-Lobed Profile Seal Ring (Quad-Ring® Type)
Available now on the Airparts.aero Marketplace.
The MS29512-06 is a high-performance, four-lobed seal manufactured in strict accordance with Military Standard MS29512. While often used in applications where a standard O-ring might be found, its X-shaped cross-section offers significant engineering advantages, providing a more stable and redundant seal. It is a flight-critical component, commonly specified by Lycoming and other engine manufacturers for sealing fuel injector nozzles at the cylinder head. Its purpose is to prevent both the leakage of raw fuel onto the hot cylinder and the ingress of unmetered air (induction leak) into the intake port.
This seal is fabricated from a Fluorocarbon (FKM) elastomer, commonly known as Viton®, a material specifically chosen for its superior resistance to the degrading effects of aviation gasoline (Avgas), high temperatures, and engine oil. The integrity of the fuel and induction system at each individual cylinder depends on the superior sealing performance of this precision, four-lobed seal.
Key Features
Military Standard (MS) Certified: Manufactured to the exact material and dimensional tolerances of the MS29512 specification, ensuring reliable performance.
Four-Lobed Profile for Superior Sealing: The X-shaped cross-section provides two distinct sealing surfaces on each side, creating a more stable and redundant seal compared to a standard O-ring.
Fluorocarbon (FKM/Viton®) Material: Offers exceptional resistance to aromatic hydrocarbons in fuel, high temperatures at the cylinder head, and engine oil, preventing swelling or hardening.
Prevents Fuel and Induction Leaks: Creates a positive seal that both contains fuel pressure and prevents unmetered air from leaning out the mixture for that cylinder.
Resists Spiral Twist: The square-like profile of the four-lobed design is inherently stable and resists the twisting and rolling in the groove that can lead to the failure of standard O-rings.
Technical Specifications
Part Number: MS29512-06
Component Type: Four-Lobed Seal Ring (Quad-Ring® Type)
Governing Specification: MS29512
OEM Applicability: Lycoming Engines, Continental Motors, and other manufacturers requiring MS-standard seals.
Material: Fluorocarbon (FKM), Viton®.
Hardness: 75 Durometer Shore A
Size (AS568A Dash Number): -006
Dimensions:
Inside Diameter: 0.114 inches (2.90 mm)
Cross-Section: 0.070 inches (1.78 mm)
Engine Compatibility
The MS29512-06 is a standard hardware component used on nearly all fuel-injected reciprocating aircraft engines. It is the specified seal for fuel injector nozzles on the vast majority of fuel-injected Lycoming engines, including but not limited to:
IO-320, IO-360, LIO-360, AEIO-360 Series
IO-540, TIO-540, LTIO-540, AEIO-540 Series
IO-580 and IO-720 Series
Crucial Note: The correct part number for a specific application must be verified against the engine's Illustrated Parts Catalog (IPC) or maintenance manual.
Fits in
- Bombardier Challenger 300
- Bombardier Challenger 601
- Bombardier Challenger 604
- Bombardier Challenger 605
- Bombardier Global Express
- Bombardier Learjet 40
- Bombardier Learjet 45
- Bombardier Learjet 55
- Bombardier Learjet 60 - all variants
- Dassault Falcon 2000 all variants
- Dassault Falcon 900 all variants
- Embraer Legacy 600-650
- Gulfstream G-IV/GIV-SP/G-400/G-450/G-300
- Gulfstream G-V/G-V-SP/G-550/G-500
- Pilatus PC-12
- Piper Aircraft PA-42 Cheyenne
- Textron Aviation Beechcraft King Air 100 - all variants
- Textron Aviation Beechcraft King Air 200 - all variants
- Textron Aviation Beechcraft King Air 300 - all variants
- Textron Aviation Beechcraft King Air 90 - all variants
- Textron Aviation Beechcraft Premier
- Textron Aviation Bell 206 Jetranger/Longranger
- Textron Aviation Cessna 500 Citation I-ISP
- Textron Aviation Cessna 510 Citation Mustang
- Textron Aviation Cessna 525 Citation Citationjet
- Textron Aviation Cessna 550 Citation I-II-Bravo
- Textron Aviation Cessna 560 Citation V-Ultra-Encore-Excel-XLS
- Textron Aviation Cessna 650 Citation III-IV-VI-VII
- Textron Aviation Cessna 680 Citation Sovereign
- Textron Aviation Cessna 750 Citation X
- Textron Aviation Hawker 400-400XP
- Textron Aviation Hawker 800
- Textron Aviation Hawker 800XP-850XP
- Textron Aviation Hawker 900XP
Applications
Primary Application: Sealing the base of the fuel injector nozzle where it is installed into the intake port of the cylinder head.
Required Replacement: This seal must be replaced whenever a fuel injector nozzle is removed for cleaning, inspection, or replacement. Typically, two seals are used per nozzle.
Why Choose MS29512-06?
Choosing a genuine MS29512-06 is a critical decision for both safety and engine health. The failure of a fuel injector seal can have two dangerous outcomes: an external fuel leak onto a hot cylinder creates a severe fire risk, while an internal air leak (induction leak) will cause that one cylinder to run dangerously lean, leading to extreme temperatures and potentially destructive detonation. The MS-standard part, with its advanced four-lobed design and certified FKM material, is specifically engineered to provide the reliable, long-lasting seal required for this high-stress, high-temperature environment.
The engineering superiority of the MS29512 four-lobed seal geometry over a standard O-ring (toroidal cross-section) is significant. A standard O-ring seals along a single, narrow, and potentially unstable tangent line of contact. The MS29512's X-shaped profile creates two distinct and stable sealing footprints on both the inner and outer surfaces, effectively doubling the sealing redundancy. The space between the lobes acts as a reservoir for lubricant, which reduces friction and wear in dynamic applications. Crucially, the relatively square cross-section of the four-lobed design is inherently resistant to spiral twist failure, a common failure mode for O-rings in reciprocating or oscillating applications where the ring can roll in its groove, leading to deep, helical cuts and seal failure. Furthermore, the mold's parting line (a potential source of imperfections) is located in the trough between the lobes, away from the critical sealing surfaces, eliminating a primary source of leaks that can be present in standard O-rings.
Note: This is a flight-critical, single-use component. These seals MUST be replaced with new ones every time a fuel injector nozzle is removed. Re-using a seal can lead to fuel or air leaks. Care must be taken to prevent cutting or nicking the seal during installation. The seal should be lightly lubricated with engine oil or an approved fuel-soluble lubricant prior to installation. Installation must be performed by a certified A&P mechanic in accordance with the applicable Lycoming maintenance manual.
Documentation
The definitive technical requirements for this component are detailed in Military Standard MS29512. Applicability must be confirmed via the engine's parts catalog.