Jaeger-LeCoultre Caliber 916 – Technical Overview from Document 1163_JLC (Pages 9–12)

Pages 9 through 12 of technical document 1163_JLC conclude the detailed servicing guide for the Jaeger-LeCoultre Caliber 916, with a focus on the alarm trigger system, hammer function, casing procedures, and final performance checks. These final pages consolidate the movement’s complex features and are essential for ensuring correct functionality of the alarm mechanism after full reassembly.

Page 9 – Alarm Trigger and Control Levers

This page illustrates the trigger system responsible for activating and silencing the alarm:

• Trigger lever and cam mechanism

• Alarm on/off slider system, controlled via the secondary crown

• Coupling clutch that links the alarm train with the hammer assembly

• Return spring that resets the alarm train after sounding

The drawing highlights precise positions of each lever and the interaction between the cam and alarm disc.

Watchmaker notes:

• Alignment of the trigger lever and cam teeth is critical—incorrect positioning may cause the alarm to fail or activate at the wrong time.

• Inspect the return spring tension to ensure the system resets correctly after the alarm finishes.

• The on/off lever must move freely; apply minimal lubrication to the pivot only.

Page 10 – Hammer, Pin, and Resonance Function

The focus here is on the alarm hammer assembly and how it interacts with the resonance pin or gong inside the case:

• Hammer arbor, striking arm, and hammer pin spring

• Placement of the contact pin or tone plate within the case interior

• Final positioning of the hammer relative to the pin when fully cocked

Watchmaker notes:

• Do not lubricate the hammer pivot—any lubricant here will dampen the alarm sound.

• Ensure the hammer has a clean, free swing; if there's resistance, check for contact friction or over-tightened screws.

• During test assembly, confirm the hammer strikes with force and resonance. A weak or dull sound suggests incorrect pin alignment or loss of spring tension.

Page 11 – Casing the Movement and Crown Configuration

This page describes the steps for installing the movement into the case and managing the dual crown system:

• Crown stem length and seating

• Alarm time-setting crown linked to the rotating disc

• Main crown with three functions: winding, time-setting, and manual alarm barrel winding

It also includes details on aligning the dial feet and properly securing the case clamps and screws.

Watchmaker notes:

• Verify crown stems are cut to correct length; improper length causes setting issues or incomplete winding.

• The alarm disc should rotate without friction when the alarm crown is turned. Any resistance could indicate dial misalignment or rubbing beneath the hands.

• After casing, retest the winding and alarm functions to ensure smooth actuation from the exterior.

Page 12 – Final Testing Procedures and Timing Adjustments

This final page outlines performance testing and tolerances:

• Timing test across multiple positions (dial up, dial down, crown down, crown left)

• Beat error target: less than 0.5 ms

• Amplitude goal: 270–300 degrees, fully wound, dial-up

• Alarm duration: Approximately 10–15 seconds, depending on barrel wind

Watchmaker notes:

• Let the movement run for 24 hours after full service to monitor amplitude consistency and alarm performance.

• If the alarm duration is short, inspect the alarm barrel and mainspring for loss of power or friction.

• When finished, perform a full winding and activation test to verify smooth rotor operation and proper automatic winding for the timekeeping barrel.

Conclusion

Pages 9 through 12 of document 1163_JLC provide the final procedures for completing service on the Jaeger-LeCoultre Caliber 916, focusing on the alarm trigger system, hammer mechanism, casing, and performance verification. This section is essential for ensuring the alarm sounds with strength and reliability and that all functions operate as intended after reassembly. Proper attention to these final steps helps preserve the character and mechanical integrity of one of Jaeger-LeCoultre’s most iconic movements.