Seiko 2502A - Parts List
Seiko 2502A – Technical Guide
The Seiko 2502A is a compact, manual-winding mechanical movement with a date complication, developed for ladies' wristwatches during the late 1960s to early 1970s. Part of Seiko’s 25xx series, the 2502A builds upon the minimalist foundation of the 2501A by adding a date display while maintaining the slim profile and high-beat operation needed for elegant, smaller timepieces.
It reflects Seiko’s design philosophy of delivering functional, reliable, and serviceable movements even in their smallest watches.
1. Technical Specifications
| Specification | Detail |
|---|---|
| Caliber Number | Seiko 2502A |
| 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 |
| Hacking Seconds | No |
| Calendar | Date (non-quickset) |
| Diameter | Approx. 17 mm (7¾ lignes) |
| Height | Approx. 3.3 mm |
| Shock Protection | Yes (Diashock on balance staff) |
2. Key Features
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Time and date display in a compact, hand-wound movement.
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No quickset: Date is advanced by rotating hands past midnight.
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Designed for slim and stylish ladies' watches from the vintage era.
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High-beat movement (21,600 bph) for improved precision and a smoother hand sweep.
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17-jewel architecture offers good wear protection in such a small format.
3. Calendar Operation
To Set the Date:
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Pull the crown to the time-setting position.
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Turn the hands past 12:00 AM to advance the date by one.
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Repeat 24-hour cycles until the correct date is reached.
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Push crown back in when finished.
⚠️ As with all non-quickset movements, avoid turning hands backward over midnight repeatedly. This can damage the calendar mechanism.
4. Movement Construction
Dial Side:
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Date disc with jumper and driving wheel
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Motion works: Cannon pinion, hour and minute wheels
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Setting system: Stem, sliding pinion, and clutch
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Simple calendar mechanism placed under the dial
Back Plate:
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Manual winding gear train with ratchet and click
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Mainspring barrel
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Center, third, fourth, and escape wheels
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Pallet fork and balance wheel
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Regulator with fine adjustment arm
The design is built to conserve space and height while still offering stable timekeeping.
5. Servicing Guidelines
Recommended Interval:
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Every 4–6 years depending on use
Typical Service Includes:
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Full disassembly of gear train, calendar, and balance assembly
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Cleaning using ultrasonic solution or traditional method for delicate parts
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Inspection of pivots, jewels, mainspring, and teeth wear
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Lubrication at all critical points (escapement, train pivots, calendar)
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Regulation with a timing machine (target: ±20–30 sec/day)
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Assembly with proper torque for hands and calendar alignment
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