A1633-39 - McCauley Propeller Genuine OEM Preformed O-RING

A1633-39 – McCauley Propeller Genuine OEM Preformed O-Ring

Available now through the AirParts Aero marketplace.

Overview Section

The McCauley A1633-39 is a genuine OEM (Original Equipment Manufacturer) preformed O-ring designed specifically for the hub and pitch-change mechanisms of McCauley constant-speed and full-feathering propellers. This high-precision seal is a critical component in maintaining the hydraulic integrity of the propeller system, which relies on pressurized engine oil to adjust blade pitch.

The -39 dash number refers to its specific dimensional profile and material composition. As a "preformed" packing, it is engineered to seat perfectly within the machined grooves of McCauley propeller components, preventing oil leaks that can lead to "surging" RPM, loss of pitch control, or messy oil spray on the aircraft windshield.

Key Features Section

• Aviation-Grade Elastomer: Manufactured from a specialized synthetic rubber compound (typically Nitrile or Fluorocarbon) optimized for constant exposure to warm engine oil.

• Hydrocarbon Resistance: Specifically formulated to resist the "swelling" and "hardening" effects of MIL-L-22851 and MIL-L-6082 ashless dispersant engine oils.

• Low Compression Set: Engineered to maintain its "spring-back" force against the sealing surfaces, even after years of being compressed under high centrifugal loads.

• Thermal Stability: Maintains a flexible, airtight seal across a wide temperature spectrum, from the cold-soak of high-altitude flight to the high-heat environment of the engine nose case.

• Precision Cross-Section: Features a uniform, flash-free finish to ensure 100% surface contact within the propeller hub gland.

• OEM Integrity: Unlike aftermarket seals, the A1633-39 meets the exact stretch and Shore A durometer (hardness) requirements specified by McCauley’s engineering team.

Technical Specifications Section

Aircraft Compatibility Section

The A1633-39 is used across a broad range of McCauley propeller models found on various high-performance aircraft:

• Cessna Fleet: Found in the constant-speed propellers of the Cessna 182 Skylane, 206 Stationair, and 210 Centurion.

• Beechcraft Models: Utilized in certain Bonanza and Baron propeller hub assemblies.

• General Aviation: Compatible with many McCauley 2-blade and 3-blade "threaded" and "threadless" hub configurations.

Technical Applications & Safety

In a constant-speed propeller system, the O-rings are the only things standing between the propeller governor's oil pressure and a total loss of pitch control.

Safety Warning: Installation and Lubrication.

When installing the A1633-39, never use sharp metal tools (like screwdrivers) to seat the O-ring, as even a microscopic nick can lead to a high-pressure leak.

Propeller "Surging": If you notice your engine RPM fluctuating or "hunting" for the set RPM, it may be a sign that an internal hub O-ring like the A1633-39 is weeping oil internally, preventing the propeller piston from maintaining constant pressure. At every 100-hour or Annual inspection, the propeller hub should be inspected for any signs of external oil seepage, which often indicates a failing O-ring.

Installation & Maintenance Addendum

1. Cure Date Check: Always verify the "Cure Date" on the sealed McCauley packaging. Rubber components have a finite shelf life; installing an "expired" O-ring can lead to premature failure due to ozone cracking.

2. Lube Prior to Install: Lightly coat the O-ring with clean engine oil or a McCauley-approved lubricant (such as Mobilgrease 28, if applicable to the specific hub model) to ensure it slides into the groove without twisting or "scuffing."

3. Cleanliness: Ensure the propeller hub gland is surgically clean. Even a single grain of sand or a speck of old dried oil can create a leak path that the O-ring cannot bridge.