Jaeger-LeCoultre Calibers 240–245 – Technical Overview from Document 1093_JLC (Pages 1–6)

The Jaeger-LeCoultre Calibers 240 to 245 represent a family of manual-winding mechanical movements crafted during the mid-20th century. These calibers are known for their robustness, precision, and versatility, with variations tailored to different display configurations including small seconds and central seconds, as well as added complications like date functions. Document 1093_JLC, pages 1 through 6, provides an in-depth technical breakdown focusing on these movements’ construction, key features, and servicing protocols.

General Technical Specifications (Common Features)

Type: Manual-winding
Functions: Hours, minutes, with variations including small seconds, central seconds, and date
Jewels: Typically 17 to 19, depending on the variant
Frequency: 18,000 vibrations per hour (2.5 Hz)
Power Reserve: Approximately 40 hours
Diameter: Approximately 27–28.3 mm
Height: Ranges from about 3.5 mm to 4.0 mm, depending on complications

Caliber Variations

Caliber 240: Basic time-only movement with small seconds subdial, classic architecture, and reliable performance.
Caliber 241: Similar to Caliber 240 but with central seconds replacing the small seconds.
Caliber 242: Builds upon the prior versions by adding a date complication, typically displayed via a date window at 3 o’clock.
Caliber 243: Often a variant combining features of central seconds and calendar complications.
Caliber 244 and 245: Higher-end or specialized versions incorporating further refinements such as improved shock protection or finishing.

Movement Architecture and Features (Pages 1–6 Highlights)

The base movement architecture consists of a sturdy gear train, manual winding barrel, and a robust escapement, designed for consistent energy delivery and precision.
Variations in the seconds display (small seconds vs. central seconds) affect the fourth wheel and motion works configuration.
The calendar mechanism includes a date-driving finger on the hour wheel and a semi-instantaneous date jump system with a jumper spring and date disc.
Fine adjustments are enabled via a micro-regulator on the balance cock.
The movement features shock protection systems (Incabloc or equivalent) on the balance staff for enhanced durability.

Servicing and Lubrication Notes

Critical lubrication points include escape wheel pivots, pallet stones, balance staff jewels, and barrel arbor, with appropriate synthetic oils used for each.
The calendar system requires minimal lubrication at friction points to prevent sluggish date changes or skipping.
Proper adjustment of the date jumper spring is essential to ensure accurate and reliable date advancement.
Watchmakers should verify the free movement of the seconds hand assembly and ensure smooth manual winding with no excessive resistance.
Regulation targets include an amplitude of approximately 270° and a beat error below 0.8 ms for optimal timing performance.

Applications

Calibers 240 through 245 were used in a variety of Jaeger-LeCoultre wristwatches:

Classic dress watches featuring small or central seconds and optional date windows.
Cases crafted from stainless steel, gold, or platinum, generally sized between 34 and 37 mm.
Models designed for buyers who valued traditional aesthetics combined with reliable mechanical engineering.

Conclusion

Pages 1 through 6 of document 1093_JLC provide a thorough technical foundation for understanding, servicing, and appreciating the Jaeger-LeCoultre Calibers 240 to 245. These movements exemplify mid-century mechanical watchmaking with their balance of precision, durability, and functional variety. They remain important calibers in JLC’s horological heritage and continue to be favored by collectors and watchmakers for their classic design and dependable performance.