468-341 – Piper Aircraft OEM Fuel Primer Jet / Primer Nozzle
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Overview Section
The Piper Aircraft 468-341 is an Original Equipment Manufacturer (OEM) Fuel Primer Jet or Primer Nozzle. This component is a critical, low-flow metering device used in the fuel system of many classic Piper piston-engine aircraft. Its purpose is to atomize and inject a controlled, measured amount of raw fuel directly into the engine's induction system (intake manifold or cylinder ports) to aid in starting a cold engine. This action, known as priming, creates the necessary fuel-air mixture richness for initial ignition, a process that is essential before the carburetor or fuel injection system takes over.
The jet is a precision-machined stainless steel or brass fitting that controls the flow rate of the fuel drawn from the primer pump (plunger or electric). As a certified OEM part, it ensures the correct metering and spray pattern, which is crucial for preventing over-priming (leading to a hydraulic lock or fouled plugs) or under-priming (leading to a hard start).
Key Features Section
Fuel Metering Function: Contains a precise internal orifice that controls the rate and amount of fuel delivered during the priming cycle.
Cold Start Aid: Provides the necessary rich fuel-air mixture required for initial ignition of a cold piston engine.
OEM Certified Quality: Manufactured to Piper Aircraft's specifications for material, flow rate calibration, and thread dimensions.
Corrosion Resistance: Constructed from Stainless Steel (SS) or brass to resist corrosion and degradation from aviation gasoline (Avgas).
Direct Injection: Designed to be installed at the intake manifold or directly into the cylinder head port to ensure fuel is precisely atomized near the intake valve.
Standardized Threading: Features standard aviation pipe threading (e.g., NPT or equivalent) for secure and leak-free installation into the fuel lines.
Technical Specifications Section
Part Number: 468-341
Component Type: Fuel Primer Jet / Primer Nozzle / Fuel Fitting
OEM Manufacturer: Piper Aircraft, Inc.
Material: Stainless Steel (SS) or Brass (Often superseded by part number 31197-000 or a certified PMA part like U31197-000)
Configuration: Straight-type fitting with a metering orifice.
Thread Type: Pipe thread or machine thread (Specific size must be confirmed by installation drawing).
Application: Engine Fuel Priming System.
Governing Specifications: Certified under FAA-PMA/OEM standards for use in Piper aircraft fuel systems.
Aircraft Compatibility Section
Piper J-3 Cub and Derivatives: J-3, J-5 (later serial numbers).
Piper PA-11, PA-12, PA-14, PA-15, PA-16, PA-18 (Super Cub).
Piper PA-20 (Pacer), PA-22 (Tri-Pacer).
Piper PA-24 (Comanche), PA-25 (Pawnee).
Piper PA-28 (Cherokee) Series: Used in early models with plunger-type manual priming systems.
Note: This part has extensive applicability across the classic Piper fleet. The aircraft’s Illustrated Parts Catalog (IPC) is the final authority for verifying the exact part number and the required number of jets (one per cylinder or one per manifold location).
Applications Section
Pre-Start Priming: Injecting fuel before the magnetos are switched on and the starter is engaged.
Restart Priming: May be used to prime a warm engine that has been shut down for a short period and is difficult to restart.
Fuel Line Connection: Serves as the terminal connection point between the primer pump line and the engine manifold or cylinder port.
Why Choose the 468-341?
The 468-341 is a flight-critical engine fuel system component. The precise metering provided by the factory-calibrated orifice is essential for safe engine starting. Using an uncertified fitting with an incorrect orifice size risks: 1) Vapor Lock: Incorrect flow could lead to vapor lock in hot conditions; 2) Over-Priming: Flooding the engine, risking catastrophic hydraulic lock where liquid fuel in the cylinder prevents the piston from reaching Top Dead Center (TDC), potentially bending the connecting rod; or 3) Leaking: An improper thread or sealing surface could lead to a fuel leak in the hot engine compartment, posing a severe fire hazard. The OEM-certified jet guarantees the correct flow rate, thread integrity, and material safety required for the aviation fuel system.
The proper function of the 468-341 jet is based on the principle of fuel atomization. The jet's small, precisely sized orifice converts the liquid fuel pressure from the primer pump into a fine, conical mist as it enters the low-pressure intake system. This atomized mist is crucial because liquid fuel cannot burn; only fuel in its vaporized state can combine effectively with air for combustion. If the jet is damaged or replaced with one having an oversized orifice, the fuel enters as a stream rather than a mist, leading to poor vaporization, inefficient priming, and the aforementioned risk of hydraulic lock if too much liquid fuel pools in the cylinder.
Note: The 468-341 is a life-critical engine component. It must be installed using the correct thread sealant (if specified) and torqued to the value specified in the Engine Installation Manual to prevent fuel leaks. The entire primer system must be checked for proper flow and leak-free operation after installation by a certified A&P mechanic.
Documentation
Piper Aircraft Illustrated Parts Catalog (IPC): Required for definitive part number verification by engine model and location.
Lycoming or Continental Engine Installation Manual: Contains torque specifications and primer system operation details.