The Jaeger-LeCoultre Caliber 918, as detailed in technical document 1166_JLC 918 Pages 7–9, continues to reveal the advanced design and fine mechanics of one of JLC’s most sophisticated movements. These pages focus on key aspects of the final stages in assembly, including regulation, alarm setting mechanics, and casing procedures. Below is a structured breakdown of the likely content covered in these pages.

Caliber 918 Overview (Recap)

• Movement type: Automatic with mechanical alarm

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

• Frequency: 28,800 vibrations per hour (vph)

• Power reserve: Approximately 45 hours for timekeeping and 20–25 hours for the alarm mechanism

• Barrel system: Dual—automatic winding for time, manual winding for alarm

• Special mechanism: Alarm regulation via flywheel for controlled vibration duration

Pages 7–9 Content Overview

Page 7 – Regulation and Timing Adjustments

This section likely includes detailed instructions and diagrams for regulating the movement and ensuring optimal performance.

• Instructions for adjusting the balance wheel and fine timing via regulator screws

• Overview of amplitude and beat error control

• Focus on the alarm flywheel regulator, which controls the speed and vibration of the alarm strike

• Lubrication points specific to the escapement and alarm timing components

• Testing procedures for both timekeeping accuracy and alarm consistency

This stage is crucial for ensuring that both the timekeeping and the alarm mechanism perform reliably and with precision.

Page 8 – Alarm Setting Mechanism and Crown Functionality

This page likely outlines the functional positions of the crown and the internal gearing responsible for setting both the time and alarm.

• Description of the crown’s multiple positions:

  • Position 0: manual winding of the main barrel

  • Reverse winding direction: manual winding of the alarm barrel

  • Position 1: time-setting

  • Position 2: alarm hand setting

• Explanation of the alarm engagement lever and its interaction with the crown or a push-button

• Layout of gear trains connecting the alarm disc to the dial

• Notes on synchronizing the alarm hand with the main time display

Clear documentation of these functions ensures proper operation and helps avoid damage during assembly or servicing.

Page 9 – Casing and Final Assembly Instructions

The final section likely details the steps required to install the movement into the case safely and ensure all external mechanisms function correctly.

• Guidelines for mounting the rotor and movement into the case without disrupting the alarm gongs

• Alignment of alarm hammers, gongs, and caseback to avoid contact or muffling

• Integration of case-mounted parts, such as alarm pushers or on/off selectors

• Quality control steps including:

  • Alarm duration and clarity check

  • Date advancement timing

  • Final rate and amplitude confirmation

Final casing ensures the movement’s performance is preserved within the complete watch.

Summary

Pages 7 to 9 of the Jaeger-LeCoultre Caliber 918 technical documentation cover some of the most critical steps in the movement’s assembly and adjustment. From fine-tuning the regulation system and alarm mechanics to ensuring the correct interaction of the crown and calendar, these pages demonstrate the complexity and precision required to complete one of JLC’s most celebrated calibers.

The Caliber 918 remains a hallmark of Jaeger-LeCoultre’s innovation, and the information in these pages supports its long-standing reputation as one of the finest mechanical alarm movements ever produced.