Seiko 2451 - Parts List
Seiko 2451 – Technical Guide
The Seiko 2451 is a vintage mechanical manual-wind movement with a date complication, designed for use in ladies’ wristwatches during the late 1960s and early 1970s. A member of the 24xx series, the 2451 represents Seiko’s effort to deliver compact, reliable, and elegant calibers tailored to smaller watch cases. Despite its small size, it includes a full date mechanism and offers respectable performance and durability for its class.
1. Technical Specifications
| Specification | Detail |
|---|---|
| Caliber Number | Seiko 2451 |
| Movement Type | Mechanical – Manual winding |
| Functions | Hour, Minute, Date |
| Jewels | 17 |
| Beat Rate | 21,600 vibrations/hour (6 beats/sec) |
| Power Reserve | ~40 hours |
| Manual Winding | Yes (no automatic winding) |
| Hacking Seconds | No |
| Calendar Type | Date only (non-quickset) |
| Diameter | ~17.0 mm (~7 ¾ lignes) |
| Height | ~3.3 mm |
2. Key Features
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Manual wind only: Wound via crown; no rotor or automatic system.
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Date window at 3 o’clock (typical layout).
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Non-quickset date: Requires advancing the time through midnight.
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Compact design: Specifically built for smaller case sizes in ladies' watches.
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Reliable beat rate: 21,600 bph provides smooth hand motion and solid accuracy.
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Jewelled movement: 17 jewels reduce wear on pivots and key gear points.
3. Calendar Operation
Since the 2451 does not have a quickset date, setting the date involves rotating the time manually.
To Set the Date:
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Pull the crown to the time-setting position.
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Rotate the hands forward past midnight to advance the date by one.
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Repeat the 24-hour cycle until the correct date is displayed.
⚠️ Avoid turning the hands backward over midnight repeatedly—it may damage the date mechanism.
4. Movement Architecture
Dial Side:
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Cannon pinion, hour wheel, and minute wheel
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Date driving wheel and date jumper
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Date disc mounted beneath the dial
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Setting mechanism with clutch and sliding pinion
Back Plate Side:
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Manual winding mechanism: crown wheel, ratchet wheel, and click
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Gear train: center, third, fourth, and escape wheels
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Pallet fork and balance wheel
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Shock protection on balance staff (usually Seiko Diashock)
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Barrel and mainspring assembly
5. Servicing Guidelines
Service Interval:
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Every 4–6 years, or when performance declines
Servicing Steps:
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Disassemble dial, calendar, gear train, and balance
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Clean components in ultrasonic cleaner or manually (hairspring)
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Inspect jewels, pivots, and mainspring
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Lubricate all pivots, escape teeth, pallet stones, and calendar parts
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Reassemble and test for amplitude and regulation
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Regulate via balance regulator arm (±20–30 sec/day acceptable for vintage)
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