Jaeger-LeCoultre Caliber 918 – Technical Overview from Document 1164_JLC (Pages 1–3)

The Jaeger-LeCoultre Caliber 918 is a refined evolution of the brand’s automatic alarm movement family, directly descended from Caliber 916. It was developed in the late 1970s and used prominently in Memovox models, particularly those with advanced case designs like the Master Réveil. Pages 1 through 3 of technical document 1164_JLC provide the structural overview, component layout, and introductory servicing details.

Page 1 – General Specifications and Architecture

This opening page outlines the fundamental attributes of Caliber 918:

• Type: Automatic, manual-wind capable

• Functions: Hours, minutes, central seconds, alarm, date

• Jewels: 28

• Frequency: 28,800 vibrations per hour (4 Hz)

• Power Reserve:

  • Timekeeping barrel: ~45 hours

  • Alarm barrel: ~20 hours

• Diameter: Approx. 30.2 mm

• Height: ~7.85 mm

• Automatic Rotor: Full-size, unidirectional on ball bearings

The caliber retains the dual-barrel layout of Caliber 916, with one barrel dedicated to the alarm and one to timekeeping, and adds a date complication for enhanced functionality.

Page 2 – Rotor and Winding System Layout

This diagram shows an exploded view of the automatic winding system, highlighting:

• Rotor (ball-bearing mounted)

• Reduction gears transferring energy to the timekeeping barrel

• Automatic bridge, reverser wheels, and click spring

• Manual winding system, integrated with the rotor for bi-directional functionality

Key observations:

• The alarm barrel remains manually wound only

• The rotor charges only the timekeeping barrel, not the alarm

• The reverser wheels are similar in layout to Caliber 916, though redesigned for improved durability and smoother winding

Assembly notes:

• Careful alignment of the rotor axle and correct lubrication of the reversers are essential

• Always inspect rotor free-play to avoid rotor rub or bearing drag during winding

Page 3 – Alarm Train and Setting Mechanism

This page shifts focus to the alarm control system, providing the core layout for:

• Alarm hammer and arbor

• Alarm-setting disc, controlled by the secondary crown

• On/off lever and cam-based trigger system

• Alarm barrel, ratchet, and click assembly

The interaction between the hour wheel finger and the alarm disc cam defines the activation moment. When the timekeeping hand reaches the preset disc time, the trigger releases the hammer to strike a pin or gong within the case.

Watchmaker notes:

• The hammer must be freely swinging and precisely aligned with the resonance pin

• The alarm disc must rotate smoothly without rubbing the dial or interfering with hands

• The on/off control must be tested both visually and functionally during reassembly

Conclusion

Pages 1–3 of document 1164_JLC provide the foundational overview of Jaeger-LeCoultre Caliber 918, covering its automatic winding structure, dual-barrel system, and mechanical alarm layout. These pages are vital for understanding how the timekeeping and alarm systems interact, as well as identifying the key assemblies that must be maintained or adjusted during service. The 918 is a robust, high-frequency evolution of the legendary Memovox engine, and this documentation ensures proper mechanical handling from the outset of any overhaul.