Seiko 4520A - Parts List
Seiko 4520A – Technical Guide
General Overview
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Caliber: Seiko 4520A
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Type: Manual-winding mechanical movement
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Manufacturer: Daini Seikosha (Seiko Instruments Inc.)
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Production Period: 1968–1970
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Movement Family: 45GS
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Primary Use: Grand Seiko 4520-8000 and 4520-8001
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Notable Feature: High-beat (10 bps), time-only caliber with Grand Seiko finishing and precision
Technical Specifications
| Feature | Specification |
|---|---|
| Winding System | Manual winding only |
| Jewels | 25 |
| Frequency | 36,000 A/h (10 beats per second) |
| Power Reserve | ~40 hours |
| Shock Protection | Diashock |
| Hacking Seconds | No |
| Calendar | None |
| Diameter | ~26.0 mm |
| Thickness | ~4.0 mm |
| Finishing | Brushed bridges, polished screws, tight tolerances |
Functional Description
The 4520A was part of the prestigious Grand Seiko 45GS series, marking the pinnacle of Seiko’s hand-wound movement development during the late 1960s. It was designed with high-frequency regulation, minimalist construction, and maximum precision, targeting or exceeding Swiss chronometer standards.
Crown Operation
| Position | Function |
|---|---|
| 0 | Manual winding |
| 1 | Time setting |
This is a time-only movement — no date, no quickset, no hacking — built to focus on simplicity and accuracy.
Performance Benchmarks
| Metric | Post-Service Target |
|---|---|
| Daily Accuracy | ±5 to ±10 seconds/day (regulated) |
| Amplitude | 250°–280° (fully wound, dial up) |
| Beat Error | ≤ 0.3 ms |
With proper servicing and regulation, the 4520A can meet modern COSC or better standards.
Watch Models Using the 4520A
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Grand Seiko 4520-8000
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Grand Seiko 4520-8001
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Case design: flat surfaces, Zaratsu polishing
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Stainless steel or gold-cap cases, 36 mm diameter
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Dials: no date, silver sunburst, “Grand Seiko” and applied “GS” at 12 o’clock
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Caseback: gold GS medallion or steel engraved Seiko logo
Servicing and Disassembly Notes
| Component | Notes |
|---|---|
| Balance Assembly | No hacking. Fine pivots — avoid excess pressure |
| Barrel and Mainspring | Replace mainspring on overhaul for best amplitude |
| Train Bridge | Supports entire gear train; handle carefully to avoid bent pivots |
| Regulator | Micrometer style — very sensitive; fine-tune slowly |
| Pallet and Escape | Watch for lubrication bleed — precise oiling is key |
The 36,000 A/h frequency increases wear over time, so lubrication and cleanliness are especially critical.
Lubrication Chart
| Location | Lubricant Type |
|---|---|
| Train Wheel Pivots | Moebius 9010 |
| Escape Wheel Teeth | Moebius 941 |
| Pallet Stones | Moebius 941 |
| Balance Cap Jewels | Moebius 9010 |
| Barrel Arbor & Bridle | Moebius 8200 |
| Keyless Works | Molykote DX |
Common Issues and Fixes
| Issue | Likely Cause | Solution |
|---|---|---|
| Low amplitude | Dirty train or tired mainspring | Clean, lubricate, and replace spring |
| Irregular timing | Overlubrication or dried pallet stones | Re-clean and oil lightly with 941 |
| Resistance during winding | Crown wheel or ratchet wheel wear | Clean and re-lubricate or replace |
| Beat error >0.5 ms | Balance or fork misalignment | Reposition and re-regulate |
Collectibility and Value
The 4520A is one of the most collectible Grand Seiko movements. It is respected for its simplicity, reliability, and role in Grand Seiko history.
| Condition | Estimated Value (Complete Watch) |
|---|---|
| Worn, unrestored | $1,500–$2,500 |
| Serviced, original dial | $3,000–$4,000 |
| Mint or boxed | $4,500–$6,000+ |
Loose movements are rare and usually used to restore original Grand Seiko 45GS references.
Comparison: 4520A vs 4500A
| Feature | 4520A | 4500A |
|---|---|---|
| Used In | Grand Seiko | King Seiko |
| Calendar | None | None |
| Beat Rate | 36,000 A/h | 36,000 A/h |
| Hacking Seconds | No | No |
| Finishing Quality | Higher (Grand Seiko grade) | Excellent but simpler |
Conclusion
The Seiko 4520A is a superb example of Seiko’s mechanical excellence. With its 10-beat high-frequency escapement, stripped-down layout, and impeccable finishing, it stands as one of the finest hand-wound movements ever produced in Japan. Whether you're servicing one, collecting, or simply admiring the history, the 4520A is an essential reference in Grand Seiko’s legacy.
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