71668 - Lycoming Crankshaft Idler Gear Assembly

71668 – Lycoming Crankshaft Idler Gear Assembly

Available now on the Airparts.aero Marketplace.

Overview

The Lycoming 71668 is a genuine OEM crankshaft idler gear assembly, a flight-critical component located within the engine's accessory drive gear train. This is not a primary drive gear, but an essential intermediary that transmits rotational force from the main crankshaft gear to other accessory gears, most notably the magneto drive gears. It also serves the crucial function of reversing the direction of rotation, ensuring the magnetos spin in the correct direction for proper ignition timing. Manufactured from high-strength, case-hardened steel, the 71668 is engineered to provide thousands of hours of reliable service in the high-stress environment of the engine's gearcase.

Key Features

• Power Transmission & Direction Reversal: Its primary function is to act as a bridge in the gear train, transmitting power and reversing the direction of rotation between the crankshaft gear and the magneto drive gears.
• Case-Hardened Steel Construction: Fabricated from a high-strength steel alloy and then case-hardened. This process creates an extremely hard, wear-resistant outer surface on the gear teeth while maintaining a more ductile core to resist the shock loads of gear meshing and prevent tooth fracture.
• Precision Machined: The gear teeth are hobbed and ground to a precise involute profile, ensuring smooth, quiet operation and an even distribution of loads between meshing gears. This precision is critical for preventing premature wear and maintaining correct timing.
• Integral Bronze Bushing: Typically supplied as an assembly with a precision bronze bushing pre-installed in the bore. This bushing acts as a durable, low-friction bearing surface for the idler gear shaft it rotates on.
• Genuine Lycoming OEM Part: As a genuine factory component, it guarantees conformance to Lycoming's stringent metallurgical standards, heat treatment processes, and quality control, ensuring the highest level of safety and performance.

Technical Specifications

• Part Number: 71668
  
• Component Type: Crankshaft Idler Gear Assembly
• Material: Case-Hardened Steel Alloy
• Bearing: Integral Bronze Bushing
• Primary Function: Transmits rotation to magneto drive gears and reverses direction.
• Installation: Installed on a fixed idler shaft within the engine accessory case.
• Certification: FAA Production Approval

Aircraft Compatibility

The Lycoming 71668 is one of the most common internal engine gears, used across a vast range of Lycoming's most popular 4-cylinder and 6-cylinder direct-drive engines.

• Common Engine Series:
  • O-320, IO-320, AIO-320, AEIO-320
  • O-360, IO-360, AIO-360, AEIO-360
  • O-540, IO-540, TIO-540, AEIO-540
• Common Aircraft Platforms:
  • A vast range of aircraft from Cessna, Piper, Beechcraft, Mooney, and numerous experimental designs that utilize the above Lycoming engine series.

Applications

The 71668 is a fundamental component for engine assembly and overhaul:

• Accessory Drive Operation: Essential for driving the engine's dual magnetos, which provide the high-voltage spark for ignition.
• Engine Overhaul: A mandatory inspection item during any engine overhaul. It is inspected for pitting, scoring, tooth wear, and bushing clearance, and replaced if any out-of-limit conditions are found to ensure the reliability of the rebuilt engine.

Why Choose 71668?

The accessory gear train is the synchronized heart of the engine, ensuring that the magnetos fire at the precise moment required for combustion. A failure of the 71668 idler gear would instantly de-synchronize and disable both magnetos, resulting in a complete loss of engine power. Using a genuine Lycoming 71668 OEM gear is the only way to ensure the part has the correct material composition, case hardening depth, and tooth profile specified by the engine's designers. For any professional engine build, the integrity of this gear is absolutely paramount.

Order Your Lycoming 71668 Idler Gear Now

Build your engine with the proven reliability and certified quality of genuine Lycoming components. Visit Airparts.aero to order your 71668 crankshaft idler gear today.

The 71668 idler gear is a classic example of a "simple idler" in a gear train. In the Lycoming accessory case, the crankshaft gear typically rotates in one direction (e.g., clockwise). For the magnetos to operate correctly, their internal rotors must spin in a specific direction. By placing the 71668 idler gear between the crankshaft gear and the magneto drive gears, the direction of rotation is reversed. The crankshaft gear (clockwise) turns the idler gear (counter-clockwise), which in turn drives the magneto gears in the correct (clockwise) direction. The precise calculation of the gear diameters and the backlash (the small clearance between meshing teeth) in this train is critical for minimizing noise and preventing the tooth impact damage that can result from engine power pulses.

Note: This is a flight-critical engine internal component. Installation must be performed by a certified A&P mechanic or at a qualified engine overhaul facility in strict accordance with the current Lycoming Overhaul Manual. Proper backlash measurements must be taken during assembly.