7801001 - Hartzell Engine Technologies 5/16 Cadmium Split Lock Washer

7801001 – Hartzell Engine Technologies 5/16 Cadmium Split Lock Washer

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Overview

The Hartzell Engine Technologies 7801001 is an OEM-certified, 5/16-inch split lock washer, engineered for critical fastening applications on Hartzell starters, alternators, and other engine accessories. This is not a generic hardware item; it is a precision-manufactured component designed to provide a specific, calculated spring force to maintain bolt preload in the severe, high-vibration environment of an aircraft engine compartment. Its primary function is to prevent the loosening of critical mounting bolts or case assembly hardware, which could otherwise lead to component failure, oil leaks, or the separation of the unit from the engine.

Manufactured from high-carbon spring steel and heat-treated for optimal mechanical properties, this washer is designed to act as a hardened helical spring. When compressed under a bolt head or nut, it exerts a continuous axial force against the fastener, creating tension that resists the vibrational and thermal cycling forces that attempt to loosen the joint. The cadmium plating provides superior corrosion protection, which is essential for components mounted on the engine. For maintaining the integrity of Hartzell engine components, using this specific, OEM-certified washer is a non-negotiable aspect of airworthy maintenance.

Key Features

• OEM Certification: Genuine Hartzell Engine Technologies part, guaranteeing correct material, hardness, and spring rate for its intended application.

• High-Carbon Spring Steel: Fabricated from through-hardened spring steel to provide consistent, reliable clamping force over its service life.

• Mil-Spec Cadmium Plating: Coated in accordance with QQ-P-416 specifications for exceptional, sacrificial corrosion resistance.

• Vibration Resistance: The split-ring, helical spring design is engineered to maintain bolt preload in high-vibration environments.

• Precision Manufacturing: Produced to tight dimensional and quality control standards, ensuring consistent performance.

Technical Specifications

• Part Number: 7801001

• Component Type: Split Lock Washer / Helical Spring Lock Washer

• OEM Manufacturer: Hartzell Engine Technologies

• Nominal Size: 5/16 inch

• Material: High-Carbon Spring Steel, heat-treated.

• Finish: Cadmium Plated, Type II (Yellow Chromate) per QQ-P-416.

• Governing Specifications: Conforms to the dimensional and material standards of ASME B18.21.1 and Hartzell's proprietary requirements.

Aircraft Compatibility

This is a component-level hardware part used in the assembly and mounting of numerous Hartzell starters and alternators. These units are factory-installed or STC'd on a vast range of aircraft powered by Lycoming and Continental engines, including but not limited to models from:

• Textron Aviation (Cessna & Beechcraft)

• Piper Aircraft

• Cirrus Aircraft

• Mooney International Corporation

Note: This is a standard hardware component for specific Hartzell assemblies. The applicable Component Maintenance Manual (CMM) or Illustrated Parts Catalog (IPC) for the starter or alternator is the final authority for determining its correct application.

Applications

• Component Mounting: Used under the heads of 5/16" (AN5) bolts to secure starters and alternators to the engine accessory case.

• Case Assembly: Secures through-bolts and other fasteners used in the assembly of the starter or alternator housing.

• High-Vibration Joints: Employed in any bolted joint on a Hartzell accessory where positive locking against vibration is required.

Why Choose 7801001?

Using a generic, commercial-grade lock washer on an aircraft engine is a critical safety risk. Such hardware lacks the certifications for material composition, heat treatment, and protective plating. An improperly heat-treated washer can either be too brittle and fracture under torque, or too soft and flatten completely, providing no locking action. An inadequately plated washer will quickly corrode, compromising the integrity of the bolted joint. The Hartzell 7801001 is a certified component engineered with a known spring rate and hardness, ensuring it performs its safety-critical locking function reliably for its entire service life.

The engineering principle of the 7801001 split lock washer is based on the mechanics of a hardened helical spring. When the fastener is torqued, the washer is flattened, and the inherent stiffness of the heat-treated spring steel creates a significant axial preload in the bolt. This preload is critical because it increases the frictional forces between the thread surfaces and under the bolt head, which is the primary resistance to loosening. Furthermore, the sharp, die-cut edges of the split are designed to "bite" or embed into the bearing surface of the nut/bolt head and the joint material. This physical embedment provides a secondary mechanical resistance to counter-rotation, particularly during transient vibration events where the bolt preload might momentarily relax. The combination of sustained spring tension and mechanical interference is what makes this simple component an effective locking device for the specific applications designated by the engine accessory manufacturer.

Note: This is a flight-critical piece of hardware. It is generally recommended to use new lock washers during the installation or re-installation of any component. Ensure that all mating surfaces are clean and dry. The washer must be installed correctly and the fastener torqued to the value specified in the relevant aircraft or engine maintenance manual. Do not reuse lock washers in critical applications as their spring properties may be degraded.

Documentation

• QQ-P-416F (Plating Specification): http://everyspec.com/QQ-SPECS/QQ-P/QQ-P-416F_22313/

• ASME B18.21.1 (Dimensional Standard): Public-facing PDFs for ASME standards are controlled documents, but the standard defines the dimensional and physical requirements for this type of washer.