Seiko 2406A - Parts List
Seiko 2406A – Technical Guide
The Seiko 2406A is a robust mechanical automatic movement with manual winding and date display, introduced in the mid-1960s. It belongs to Seiko’s early 24xx series of automatic calibers and is known for its durable construction and slim profile, making it suitable for both men’s dress watches and everyday timepieces of that era.
This guide provides a detailed overview of the Seiko 2406A, including its specifications, mechanical design, servicing instructions, and common issues.
Technical Specifications
| Feature | Details |
|---|---|
| Caliber Number | Seiko 2406A |
| Movement Type | Mechanical – Automatic with manual winding |
| Functions | Hour, Minute, Central Seconds, Date |
| Jewels | 27 |
| Beat Rate | 18,000 bph (5 beats per second) |
| Power Reserve | ~42 hours |
| Manual Winding | Yes |
| Hacking Seconds | No |
| Calendar | Date (non-quickset) |
| Rotor Type | Central bidirectional automatic winding |
| Size | ~27.6 mm diameter |
| Thickness | ~5.3 mm |
Key Features
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Automatic and manual winding options
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Full rotor winding with smooth bidirectional motion
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Date display without quickset function (advance by turning hands)
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Mid-beat rate (18,000 bph) for a balance of smoothness and longevity
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27 jewels providing support across the gear train and winding mechanism
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Solid and reliable movement, commonly found in Seiko's early 1960s-1970s models
Movement Layout
Dial Side:
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Motion works (hour, minute, and setting system)
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Date driving wheel
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Calendar mechanism with date jumper and wheel
Back Side (Rotor Side):
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Rotor and automatic winding assembly
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Mainspring barrel
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Gear train: center wheel, third, fourth, escape wheel
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Balance wheel, pallet fork, and escapement
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Manual winding and click mechanism
How to Set the Date (No Quickset)
To advance the date:
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Turn the hands past midnight until the date changes.
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Continue turning the hands forward 24 hours at a time to reach the correct date.
⚠️ Do not turn the hands backward over midnight repeatedly—it may damage the calendar mechanism.
Servicing Instructions
Recommended Interval:
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Every 4–6 years for optimal performance
Standard Service Steps:
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Disassemble the dial, calendar, rotor, gear train, and escapement
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Clean parts in an ultrasonic machine or manually (balance/hairspring)
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Inspect pivots, jewels, and mainspring for wear or damage
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Lubricate key components: barrel arbor, escapement, train pivots, calendar jumper
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Reassemble and regulate using a timing machine (target ±30 sec/day)
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Test amplitude and power reserve post-service
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