840-515 – Rotax OEM Socket Head Allen Screw (M5 x 18)
Available now on the Airparts.aero Marketplace.
The Rotax 840-515 is a high-precision, OEM-certified M5 x 18mm socket head Allen screw engineered for critical mounting applications within Rotax two-stroke aircraft engines. Specifically designed for high-vibration environments, this fastener is a primary component in the attachment of the magneto generator assembly and the starting pulley system. In the exacting world of light-sport aviation (LSA) and ultralight engines, the integrity of engine-mounted accessories depends entirely on the tensile strength and fatigue resistance of its hardware.
This fastener is manufactured to rigorous aerospace and automotive standards to ensure that it maintains its clamping force under the thermal cycling and high-frequency oscillations typical of Rotax 447, 503, 582, and 618 series engines. By utilizing a socket head design, the 840-515 allows for higher torque application in confined spaces compared to traditional hex-head bolts, ensuring a secure "positive lock" when installed with the correct torque values and thread-locking compounds. For mechanics and engine builders, using genuine Rotax hardware is essential to maintaining the type-certified reliability of the powerplant.
Key Features
High-Strength Alloy Steel: Forged from premium-grade steel to provide high tensile strength and resistance to shear forces within the magneto assembly.
Precision Internal Hex Drive: The socket head (Allen) design facilitates easy access in the compact spatial envelopes of the engine’s rear crankcase and ignition sections.
Engineered Thread Pitch: Features a standard M5 metric thread with high-tolerance machining to prevent cross-threading and ensure uniform preload.
Corrosion-Resistant Coating: Typically finished with a black-oxide or zinc-chromate treatment to resist environmental degradation and galvanic corrosion when in contact with aluminum engine cases.
Vibration Resistance: Designed to operate in high-RPM environments where harmonic resonance can lead to fastener backing and subsequent accessory failure.
Technical Specifications
Part Number: 840-515
Component Type: Socket Head Cap Screw (Allen Screw)
OEM Manufacturer: BRP-Rotax
Thread Size: M5
Length: 18 mm
Drive Type: Internal Hex (Allen)
Material: High-Strength Alloy Steel
Hardness Grade: Typically 8.8 or 10.9 (Verify via OEM CMM)
Standard: Metric DIN 912 / ISO 4762 Equivalent
Application: Magneto / Generator / Starting Pulley
Aircraft Compatibility
Rotax 447 UL: Used in various ignition and shroud configurations.
Rotax 503 UL: Primary fastener for magneto generator attachment.
Rotax 582 UL / 618 UL: Critical for starting pulley and stator plate mounting.
BRP/Sea-Doo/Ski-Doo: Cross-compatible with various Bombardier recreational powerplants utilizing the Rotax base.
Note: The engine's Illustrated Parts Catalog (IPC) for your specific engine model and serial number is the final authority for hardware verification.
Applications
The 840-515 is predominantly utilized in the Ignition and Magneto System. Its primary role is to secure the stator plate and the starting pulley to the crankcase. In these applications, the screw must resist the centripetal forces and vibration loads generated by the flywheel and engine crankshaft.
Why Choose 840-515?
Choosing the Rotax 840-515 ensures that your engine assembly adheres to the original design specifications of the manufacturer. Using generic "hardware store" M5 screws in a flight-critical engine assembly introduces risks of hydrogen embrittlement, incorrect tensile ratings, and premature fatigue failure. Genuine Rotax hardware provides the peace of mind that the fastener has been tested for the specific thermal and mechanical stresses of the 2-stroke aviation environment, significantly reducing the risk of an engine-out event caused by accessory detachment.
The engineering of the Rotax 840-515 revolves around the Torque-Tension Relationship within a high-vibration environment. As an M5 fastener, it is designed to achieve a specific preload that creates enough friction between the joined surfaces—such as the stator plate and the crankcase—to prevent lateral movement. In aviation engines, fasteners are subject to high-cycle fatigue due to engine harmonics. The socket head cap screw design is superior in these applications because it allows for the use of a high-strength alloy that can withstand significant axial tension without the risk of the head shearing off under torsional stress. Furthermore, the use of a socket drive allows for a smaller head diameter relative to a hex bolt, enabling the fastener to be recessed into counterbored holes, which protects the fastener from external mechanical damage and provides a cleaner aerodynamic and structural profile within the engine's internal assemblies.
Note: This is a critical engine fastener. Installation must be performed in accordance with the Rotax Heavy Maintenance Manual. It is highly recommended to use a medium-strength thread-locking compound (such as Loctite 243) and a calibrated torque wrench to reach the OEM-specified torque (typically 6 Nm for M5 in aluminum cases). Never reuse a fastener that shows signs of thread stretching or corrosion.