73249 - Lycoming Crankshaft Front Thrust Washer

73249 – Lycoming™ Crankshaft Front Thrust Washer

Available now on the Airparts.aero Marketplace.

The Lycoming 73249 is a flight-critical, genuine OEM precision thrust washer. This component is indispensable for the safe and reliable operation of the engine, as it performs two primary functions: it absorbs the immense forward-pulling (axial) thrust load generated by the propeller, and it precisely controls the crankshaft's fore-and-aft movement, known as end play. Installed at the front main bearing location within the crankcase, this two-piece washer acts as a plain bearing against which the crankshaft's forward thrust face rotates.

This is not a simple hardware washer; it is a sophisticated tribological component. It is constructed from a steel backing for structural integrity, with a bonded layer of a specialized copper-lead bearing alloy on the wear face. This surface features precisely machined oil galleries that are essential for distributing a film of high-pressure engine oil, allowing the crankshaft to float on a hydrodynamic film and preventing direct metal-to-metal contact. The thickness of this washer is one of the most critical dimensions in the entire engine, as it directly determines the final crankshaft end play.

Key Features

• Genuine Lycoming OEM Part: Guarantees the correct material composition, alloy bonding, and exacting dimensional tolerances required for this critical application.

• Manages Propeller Thrust Loads: Engineered to withstand the thousands of pounds of continuous axial force generated by the propeller, preventing crankshaft movement.

• Sets Critical Crankshaft End Play: The washer's precision-ground thickness is the primary determinant of the crankshaft's axial clearance, a critical parameter for engine health.

• Steel-Backed Copper-Lead Construction: A robust, multi-layer design that provides structural support from the steel backing and a durable, low-friction, and sacrificial wear surface from the copper-lead alloy.

• Integrated Oil Distribution Grooves: Features machined channels on the bearing face that ensure a constant, evenly distributed supply of pressurized oil to the entire thrust surface, enabling hydrodynamic lubrication.

Technical Specifications

• Part Number: 73249

• Component Type: Crankshaft Thrust Washer (Plain Bearing)

• OEM Manufacturer: Lycoming Engines

• Application Location: Front Main Bearing Saddle, Crankcase.

• Construction: Two-piece (split), Steel-Backed Copper-Lead Alloy.

Engine Compatibility

The 73249 thrust washer is one of the most widely used parts in the Lycoming ecosystem and is specified for the majority of direct-drive Lycoming engine families, including but 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

• IO-580 Series

• IO-720 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.

Applications

This thrust washer is a mandatory replacement part during any maintenance that requires the separation of the crankcase halves.

• Complete Engine Overhaul

• Crankcase or Crankshaft Replacement

• Any maintenance requiring removal of the crankshaft.

Why Choose 73249?

Choosing a genuine Lycoming 73249 thrust washer is an absolute necessity for a reliable engine build. The thickness of this single component directly sets the crankshaft end play, a clearance critical to the engine's performance and longevity. Using a non-certified part risks incorrect dimensions, which can lead to insufficient clearance, causing oil starvation and seizure, or excessive clearance, causing crankshaft "hammering" and damage to the gear train. Furthermore, an improper bearing alloy can wear rapidly or fail, leading to a total loss of engine oil pressure. For this flight-critical plain bearing, there is no substitute for the guaranteed quality and precision of a genuine Lycoming component.

The 73249 thrust washer operates on the principle of hydrodynamic lubrication to manage the immense axial loads from the propeller. In a tractor aircraft configuration, the propeller is constantly pulling the crankshaft forward with a force that can be thousands of pounds. This force is transmitted from the crankshaft's thrust face to the stationary 73249 washer. The washer's machined oil galleries are not merely for cooling; they are critical for establishing a high-pressure oil film. As the crankshaft rotates, it drags viscous engine oil into the microscopic, converging wedge-shaped space between itself and the washer's bearing surface. According to the principles of Reynolds lubrication theory, this action generates an extremely high-pressure hydrodynamic film that physically separates the two metal surfaces. The crankshaft thrust face literally floats on this constantly regenerating film of oil, preventing metal-to-metal contact and minimizing frictional losses. The washer's copper-lead alloy is the engineered sacrificial surface, strong enough to withstand the load if the film momentarily collapses during startup or shutdown, yet soft enough to prevent damage to the hardened and polished crankshaft journal.

Note: This is a flight-critical, precision internal engine component and is a mandatory replacement during any engine overhaul. After installation and crankcase assembly, the crankshaft end play MUST be meticulously measured with a dial indicator to ensure it is within the narrow tolerance specified in the overhaul manual. The bearing surfaces must be perfectly clean and coated with a high-quality assembly lubricant prior to installation. Installation constitutes a major engine overhaul and must be performed by a certified A&P/IA mechanic in a clean-room environment, in strict accordance with the applicable Lycoming overhaul manual.

Documentation

The definitive part number applicability and all installation and clearance specifications are detailed in the applicable Lycoming engine maintenance, overhaul, and parts catalogs for the specific engine model and serial number.