72801 – Lycoming™ Engine Crankshaft Counterweight Assembly
Available now on the Airparts.aero Marketplace.
Overview
The Lycoming 72801 is a genuine OEM crankshaft counterweight assembly, a flight-critical dynamic component engineered for Lycoming's six-cylinder 540-series engines. This is not a simple static counterweight; it is a precision-manufactured dynamic counterweight, also known as a pendulum-style torsional vibration absorber. Its purpose is to counteract and cancel out the inherent torsional vibrations produced by the engine's power pulses. By actively damping these harmonic vibrations, the 72801 assembly ensures smooth engine operation, reduces stress on the crankshaft and propeller, and is fundamental to the engine achieving its full service life.
Key Features
- Torsional Vibration Damping: Its primary function is to act as a tuned pendulum absorber. It is designed to oscillate out of phase with the engine's primary torsional vibration frequency, effectively canceling out this destructive force and ensuring a smoother running engine.
- Multi-Piece Precision Assembly: Consists of several precision-machined components, including two steel counterweight plates, hardened steel bushings, and suspension pins (rollers). These components allow the counterweight to pivot slightly on the crankshaft cheek in a controlled, pendulous motion.
- High-Strength Steel Construction: All components are fabricated from high-strength, certified steel alloys and are heat-treated to withstand the immense centrifugal and inertial forces of engine operation without failure.
- Reduces Component Fatigue: By damping torsional vibrations, the counterweight assembly significantly reduces the cyclical stress on the crankshaft, propeller hub, and accessory drive train, preventing metal fatigue and increasing the service life of these critical components.
- Genuine Lycoming OEM Part: As a genuine factory component, it guarantees the correct mass, pivot length, and material specifications required for the system to be perfectly "tuned" to the specific harmonic signature of the 540-series engines.
Technical Specifications
- Part Number: 72801
- Component Type: Dynamic Crankshaft Counterweight / Torsional Vibration Damper
- Material: High-Strength, Heat-Treated Steel Alloys
- Primary Function: Cancels out crankshaft torsional vibrations.
- Installation: Mounted on the cheeks of the crankshaft at specific, designated locations.
- Certification: FAA Production Approval
- Superscedes Part: LW-19227
Aircraft Compatibility
The Lycoming 72801 is a standard factory-installed component on a wide variety of Lycoming's most popular and powerful six-cylinder engines.
- Primary Engine Series:
- Lycoming 540 Series: O-540, IO-540, TIO-540, AEIO-540
- Common Aircraft Platforms:
- Piper: PA-32 Saratoga, PA-34 Seneca, PA-24 Comanche 260
- Cessna: 182 Skylane (with Lycoming engine STC), 206 Stationair
- Mooney: M20 series (M20R Ovation, M20S Eagle)
- Van's Aircraft: RV-10
- And numerous other certified and experimental aircraft.
Applications
The 72801 is a fundamental component for engine health and smoothness:
- Engine Overhaul: A mandatory inspection and reconditioning item during any engine overhaul. The bushings and pins are wear items and are typically replaced to restore the counterweight to zero-time condition.
- Vibration Analysis & Reduction: A key component in ensuring the engine operates smoothly. Worn counterweight bushings can be a source of engine vibration and are a primary focus during dynamic propeller balancing and engine vibration analysis.
Why Choose 72801?
An undamped torsional vibration in a six-cylinder engine can lead to severe engine roughness, passenger and crew fatigue, and, in a worst-case scenario, a fatigue failure of the crankshaft or propeller. The Lycoming 72801 assembly is the specifically engineered solution that protects against this. Using a genuine Lycoming OEM assembly or an FAA-approved reconditioned unit is the only way to ensure the part has the correct mass and pivot characteristics to properly damp the vibrations of your specific engine model. For the long-term health and smooth operation of your engine, there is no substitute.
Order Your 72801 Counterweight Assemblies Now
Ensure the smooth, reliable, and long-lasting operation of your Lycoming engine with genuine OEM components. Visit Airparts.aero to inquire about new or overhauled 72801 crankshaft counterweight assemblies today.
The Lycoming 72801 functions as a centrifugal pendulum absorber. Each power stroke from a piston imparts a sharp torsional "punch" to the crankshaft, causing it to momentarily accelerate. A long, six-cylinder crankshaft is susceptible to twisting and untwisting like a spring at specific harmonic frequencies. The 72801 counterweight plates are not rigidly attached but are suspended by rollers in elongated slots on the crankshaft cheek. As the crankshaft rotates, centrifugal force holds the plates firmly outward. When a torsional vibration occurs, it causes a slight change in the crankshaft's rotational speed. This change in speed allows the counterweight plates to "swing" slightly in their suspended state, much like a pendulum. The system is "tuned" so that this swinging motion is out-of-phase with the crankshaft's vibration, creating an opposing force that actively cancels out the harmful harmonic.
Note: This is a flight-critical engine internal component. Installation and servicing 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 and relevant Service Instructions. Proper clearances and torques are essential for correct function.
Description: COUNTERWEIGHT
Part number: 72801
Replacement: LW-19227
Related Service Bulletin:
Lycoming™ Service Instruction No. 1012L [ Click Here ]
72801 used in Counterweight and Crankshaft Assemblies
Fits the following engine models:
Lycoming™ Engines
- O-360 (A1F6, -A1F6D, -A1G6, -A1G6D, -A1H6, -E1A6D, -F1A6, -G1A6)
- LO-360 (A1H6, -A1G6D, -E1A6D)
- IO-360 (A1B6, -A1B6D, -A1D6, -A1D6D,-A3B6, -A3B6D, -A3D6D, -B1G6, -B1F6, -B2F6, -C1C6, -C1D6, -C1E6, -C1E6D, -C1G6, -J1A6D)
- AEIO-360 (A1B6, -A1E6, -B1G6)
- LIO-360 (B1G6, -C1E6; -C1E6D)
- TO-360 (C1A6D, -E1A6D, -F1A6D)
- LTO-360-E1A6D
- TIO-360 (A3B6, -C1A6D)
- IO-390 (A1A6, -A3A6, -A1B6, -A3B6, -C1A6, -C3A6, -C1B6, -C3B6, -D1A6, -D3A6, -D1B6, -D3B6)
- AEIO-390 (A1A6, -A3A6, -A1B6, -A3B6)
- AEIO-540 (D4A5, -D4B5, -D4D5)
- IO-540 (A1A5, -B1A5, -B1B5, -B2B5, -B1C5, -C4B5, -C4C5, -C4D5, -C4D5D, -D4A5, -D4B5, -E1A5, -E1B5, -G1A5, -G1B5, -G1C5, -G1D5, -G1E5, -G1F5, -J4A5, -J4B5, -P1A5, -T4A5D, -T4B5, -T4B5D, -T4C5D, -V4A5, -V4A5D, -W1A5, -W1A5D)
- O-540 (A4A5, -A4B5, -A4D5, -A4E5, -B4B5, -E4A5, -E4B5, -E4C5, -J1A5D)
- TIO-540 (AA1AD, -AB1AD, -AG1A, -C1A, -E1A, -G1A, -H1A)
Lycoming™ Illustrated Parts Catalog [ Click Here ]