68H22624 – Lycoming™ Magneto Drive Gear Torsional Damper Cushion
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The Lycoming 68H22624 is a genuine OEM, flight-critical elastomeric damper cushion designed for the magneto drive gear assembly. This is not a simple rubber spacer; it is an engineered viscoelastic damper whose function is indispensable for the longevity and reliability of the engine's ignition system. Its primary role is to act as a flexible coupling, absorbing the sharp torsional shocks from the engine's power pulses and, most importantly, the violent kickback loads generated by the magneto's impulse coupling during engine start.
Manufactured from a high-durometer, oil-and-heat-resistant synthetic rubber compound, this cushion protects the delicate, high-precision internal components of the magneto—such as the distributor gear, rotor, and impulse coupling assembly—from the damaging, high-frequency shock loads of the gear train. A properly functioning cushion is the first line of defense against premature magneto wear and failure. Over time, these cushions harden and lose their damping properties, making their inspection and replacement a critical maintenance task.
Key Features
Genuine Lycoming OEM Part: Guarantees the correct elastomer compound, durometer (hardness), and dimensions required for proper damping characteristics and service life.
Absorbs Torsional Drive Shocks: Acts as a viscoelastic damper, absorbing and dissipating the sharp power pulses from the crankshaft before they reach the magneto.
Protects Magneto Impulse Coupling: Absorbs the significant kickback torque generated when the impulse coupling fires during engine start, preventing damage to the magneto and its drive gears.
High-Modulus Elastomer Compound: Precision-molded from a specialized synthetic rubber designed to resist degradation, hardening, and swelling from long-term exposure to hot engine oil.
Ensures Ignition System Longevity: A fresh, pliable cushion is one of the most important factors in ensuring the magneto reaches its full time between overhauls.
Technical Specifications
Part Number: 68H22624
Component Type: Magneto Drive Gear Damper Cushion
OEM Manufacturer: Lycoming Engines
Material: High-Durometer, Oil/Heat-Resistant Synthetic Rubber (Elastomer).
Application: Fits within the magneto drive gear assembly located in the engine's accessory case.
Engine Compatibility
The 68H22624 magneto drive cushion is used on the vast majority of direct-drive Lycoming engines equipped with impulse-coupled magnetos. Applicable engine families include, but are not limited to:
O-235, O-320, IO-320, AEIO-320 Series
O-360, IO-360, AEIO-360, TIO-360 Series
O-540, IO-540, AEIO-540, TIO-540, LTIO-540 Series
Crucial Note: The specific engine model and serial number must be checked against the latest revision of the official Lycoming Parts Catalog to ensure correct part number applicability. The engine parts catalog is the final authority.
MAGNETO DRIVE GEAR AND CUSHION MODIFICATION
Supersedes Service Instruction No. 1299A
September 24, 2010
MODELS AFFECTED
- O-360 with serial numbers up to and including 19774-36A.
- IO-360 with serial numbers up to and including 13275-51A.
- LIO-360 with serial numbers up to and including 1062-67A.
- O-540 with serial numbers up to and including 17269-40.
- IO-540 with serial numbers up to and including 12775-48.
- TIO-540 with serial numbers up to and including 3536-61a; also 3538-61A and 3539-61A.
- LTIO-540 with serial number 522-68A.
Fits Engine Models
- O-360 with serial numbers up to and including 19774-36A.
- IO-360 with serial numbers up to and including 13275-51A.
- LIO-360 with serial numbers up to and including 1062-67A.
- O-540 with serial numbers up to and including 17269-40.
- IO-540 with serial numbers up to and including 12775-48.
- TIO-540 with serial numbers up to and including 3536-61a; also 3538-61A and 3539-61A.
- LTIO-540 with serial number 522-68A.
Replaces PN LW13641
Related Lycoming Service Instruction No. 1299B [Click Here]
*For Further Information See Lycoming IPC [Click Here]
TIME OF COMPLIANCE
During overhaul or earlier at the owner’s discretion.
This revision of Service Instruction No. 1299 includes installation instructions for a new magneto drive gear P/N LW-13899 and a new matching drive cushion P/N 68H22624 that are available to replace magneto drive gear LW-13642 and drive cushion LW-13641 as a matched set.
Applications
This damper cushion is a mandatory replacement part during major engine and ignition system maintenance.
Complete Engine Overhaul
500-Hour Magneto Inspection and Repair
Any maintenance requiring the removal of the magneto and its drive gear assembly.
Why Choose 68H22624?
Choosing the genuine Lycoming 68H22624 is a critical investment in the health of your engine's ignition system. A hardened, cracked, or degraded cushion provides no shock absorption, transmitting every power pulse and impulse coupling kick directly to the magneto's gear teeth and bearings. This is a primary cause of premature magneto failure, which can lead to a loss of engine power. Using a non-certified part made from an incorrect elastomer compound risks rapid degradation in the hot oil environment, leading to a complete loss of damping capability. The genuine Lycoming part is the only way to guarantee the correct material properties and durometer required to protect your magnetos as designed by the engine manufacturer.
The 68H22624 cushion functions as a viscoelastic damper, dissipating mechanical energy through the principle of hysteresis. When a sharp torque is applied to the magneto drive gear, the elastomeric cushion deforms. Part of this deformation energy is stored elastically within the polymer's molecular chains and is returned to the system (like a spring). However, a significant portion of the energy is converted into heat due to the internal friction of these long polymer chains sliding against each other during deformation. This conversion of mechanical shock energy into low-grade thermal energy, which is then dissipated into the engine oil, is known as hysteretic damping. The effectiveness of the damper is a direct function of the material's durometer (a measure of its stiffness) and its damping coefficient. Lycoming has selected a specific elastomer compound with a durometer that is stiff enough to transmit the required drive torque without excessive rotational lag ("wind-up"), yet has a high enough damping coefficient to effectively attenuate the peak shock loads that would otherwise be imparted to the magneto's bearings and impulse coupling components.
Note: This is a flight-critical ignition system component. It is a mandatory replacement item at every engine overhaul and is highly recommended for replacement at every 500-hour magneto inspection, or any time the magneto is removed. A cushion that is found to be hardened, cracked, or swollen is unairworthy and must be replaced. Installation must be performed by a certified A&P mechanic in accordance with the Lycoming overhaul and maintenance manuals.
Documentation
The definitive part number applicability and installation procedures are detailed in the applicable Lycoming engine maintenance, overhaul, and parts catalogs for the specific engine model.