Seiko Caliber 6309

Brand	Seiko
Caliber Number	6309, 6309A
Movement Type	Automatic
Lignes	12”’
Diameter	27mm
Height	5.3mm thick
Jewels	17
Vibrations Per Hour	21,600 bph
Power Reserve	47 hours
Lift Angle	54.5 degrees (needs confirmed)
Shock System	Diashock
Rotor	Ball bearing
Mainspring	401615
Balance Staff	311601
Hands	1.5mm x 0.90mm x 0.20mm
Hacking?	No
Manual Winding?	No
Crown Location	4:00
Functions	Hours, minutes, central seconds, quickset bi-lingual day, quickset date
Country of Manufacture	Japan
Known Models	6309 (add more in the comments below…)

The Seiko caliber 6309 is a vintage automatic workhorse movement that was found in many Scuba Diver models, seiko 5, and dress watches in the 1980’s.

Note: This caliber is sometimes mistaken as being 6809 (6809A) by folks who can’t see the 3 clearly.

In Seiko’s own words:

In old Seiko documentation, they refer to the 6309 as a Highly Reliable Movement:

The highly stabilized accuracy and high reliability established for the 61XX series has been incorporated into the movement.

Also mentioning easy servicing:

Disassembling and reassembling procedures and serviceability have been improved largely by:

• Employment of a new balance hairspring holding device (aka no stud for the hairspring since it clamps directly in the terminal)
• Decrease in number of parts from the simplification of the movement structure.
• Decrease in number of new parts resulting from interchangeability of some parts with Cal. 61XX series.

Variations:

There are different variations of this movement, including Seiko caliber 6308A (17J), 6319A (21J), 6347A (moonphase, 23J), 6349A (23J).

Community Commentary:

In an interesting thread on the Military Watch Resource forum comparing the Seiko caliber 6309 to the ETA caliber 2824, shortwave said:

I have a 25 year old 6309 7290. It hasn’t been cleaned in at least 10 years. It advances 1 to 2 seconds in 12 days. I’ve never seen such accuracy in any manual watch. The ETA in my Marathon, gains seconds a day.

Video of Servicing:

Additional Resources:

• View more Seiko calibers here
• Shop Seiko watches here