Repairing Omega self-winding watches with bumper movements requires both mechanical skill and an understanding of the unique characteristics of these early automatic calibers. Bumper movements, which predate the full-rotor automatics, feature a pendulum-like mass that “bumps” back and forth rather than completing full circles. These were Omega’s solution to automatic winding in the 1940s and early 1950s.

Overview of Bumper Movements

Omega introduced bumper automatic calibers in the late 1930s and refined them through the 1940s and early 1950s. Well-known examples include:

• Caliber 28.10 (early models)

• Caliber 342, 344, 354, 355, etc.

These movements are identified by:

• A semi-circular winding mass that moves between spring bumpers

• Bidirectional winding

• A manual winding option via the crown

• Simple and accessible bridge layouts

Key Components Requiring Attention

1. Bumper Springs:
   These act as shock absorbers for the rotor. Over time, they can fatigue or break, requiring replacement.

2. Rotor Bearing and Axle:
   Excessive wear may lead to poor winding performance. Bearings should be checked for play and lubricated with high-grade oil or replaced if worn.

3. Winding Gear Train:
   The bumper rotor transmits power to the mainspring via a gear train. These gears should be disassembled, cleaned, inspected under magnification, and lightly lubricated during service.

4. Mainspring and Barrel:
   If the watch does not hold a power reserve, inspect the barrel arbor and replace the mainspring if it lacks tension or shows signs of sticking.

5. Pallet and Escape Wheel:
   Clean carefully and lubricate sparingly with epilame-treated oils or specific escapement lubricants.

Servicing Procedure Overview

1. Disassembly:
   Remove the rotor and bumper spring assembly first. Then proceed with disassembling bridges, gear train, and escapement. Take care to document spring positioning.

2. Cleaning:
   Use a watch cleaning machine with appropriate solutions. Avoid ultrasonic cleaning for fragile parts like the balance complete and pallet fork.

3. Inspection and Reassembly:
   Check jewels for cracks and pivots for wear. Reassemble while lubricating:

   • Rotor pivots and bearings with medium synthetic oil

   • Gear train pivots with light oil

   • Barrel arbor with grease

   • Escape wheel teeth with minimal application of oil

4. Regulation and Timing:
   Once reassembled, test on a timing machine. Aim for accuracy within ±15 seconds/day for most bumper calibers.

Tips and Cautions

• Spare parts for bumper calibers are increasingly rare. Consider using donor movements.

• Be gentle with bridges and screws, as some are specific to individual calibers and hard to replace.

• Do not overwind during testing—bumper mechanisms can wear under excessive torque.

Conclusion

Repairing Omega bumper automatics blends vintage charm with mechanical nuance. They represent an important era in Omega’s horological development and offer rewarding service experiences for the skilled watchmaker. Proper lubrication, careful reassembly, and patient regulation will ensure these early automatics continue ticking with historic precision.