The Bulova Calibers 245 and 246 are both vintage manual-wind movements designed for use in mid-20th-century watches, and while closely related, they feature subtle differences tailored for specific case designs or dial layouts. These calibers are compact, reliable, and relatively straightforward in construction, making them ideal for both daily wear and restoration projects.

General Specifications (245 and 246)

• Type: Manual-winding mechanical movements

• Functions: Hours, minutes, and small seconds

• Jewels: Typically 17 jewels

• Beat Rate: 18,000 vibrations per hour (vph)

• Shock Protection: Present on the balance (often Kif or Incabloc depending on market)

• Diameter: Approx. 10.5 ligne (≈23.7 mm)

• Height: Roughly 4.0 mm

Both calibers share the same base architecture, with differences often being cosmetic or involving minor layout tweaks to adapt to different watch cases or dials.

Movement Architecture and Design

• Train Layout: Both movements employ a traditional Swiss lever escapement with center, third, fourth, and escape wheels arranged under bridges.

• Balance Wheel: Large, robust balance with regulator arm for fine adjustment.

• Hairspring: Flat type, often with adjustable curb pins.

• Power Reserve: Around 40 hours from a fully wound mainspring.

• Keyless Work: Conventional winding and setting system, using a setting lever and sliding pinion.

Differences Between 245 and 246

The differences between the two are subtle and mainly involve dial foot placement or seconds hand positioning. In some versions:

• Caliber 245 may feature a slightly recessed small seconds dial.

• Caliber 246 might be adapted for watches with different hand clearances or case back tolerances.

They are otherwise functionally interchangeable in many respects, and parts can often be cross-referenced between them.

Servicing and Repair Notes

Disassembly

• Movement teardown follows standard procedures for manual calibers.

• The crown/stem pulls straight out after releasing the detent screw.

• Hands and dial must be carefully removed to access the keyless works and train bridge.

Lubrication

• Use 9010 or equivalent for train wheels and escapement.

• Apply 941 for pallet stones.

• Mainspring barrel requires re-greasing or complete mainspring replacement if degraded.

Common Issues

• Worn balance staff pivots can lead to poor amplitude.

• Dried mainspring grease may affect winding efficiency.

• Rust around the keyless work is often seen if moisture entered via the crown.

Parts Availability

As with many vintage Bulova calibers, parts are still available through specialist suppliers or donor movements. You can commonly find:

• Mainsprings

• Balance staffs

• Winding stems

• Complete train wheels

Conclusion

The Bulova 245 and 246 calibers are straightforward and durable vintage movements. Their design reflects the era's focus on reliability and serviceability, and they remain highly respected among collectors and watchmakers. Whether you're restoring a vintage Bulova or learning watch servicing basics, these calibers offer an excellent entry point with rich historical value.