Manual for NH38/NH70 seiko mod watch movement
NH38/NH70 SEIKO MOD
NH38/NH70 AUTOMATIC MOVEMENT USER MANUAL
(For Seiko Mods and Watches Using the NH38 No-Date Automatic Movement)
Overview
Your watch uses the Seiko NH38/NH70, a clean, reliable, no-date automatic movement popular in custom builds and sterile-dial mods. It’s powered by your wrist motion and can also be wound manually via the crown.
Because the NH38/NH70 has no date mechanism, operation is simpler and more robust — no calendar gears, no date-setting risks.
Case design, crown type, and water resistance vary depending on the build, so review this guide before use.
Powering the Movement
1. Automatic Winding
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The NH38/NH70 winds naturally whenever you move your wrist.
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Wearing the watch for 8+ hours per day will typically keep it fully charged.
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A full wind gives approximately 41 hours of power reserve.
2. Manual Winding
If the watch stops or hasn’t been worn recently:
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Make sure the crown is in Position 0 (fully pushed-in or screwed down).
- unscrew the crown (twist anti clockwise)
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Turn the crown clockwise around 20–30 turns.
A slipping clutch prevents overwinding, but there’s no need to force it.
Crown Operation
The NH38/NH70 works with either a screw-down crown or a standard push-pull crown.
Screw-Down Crown
Common on divers or water-resistant mods.
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Unscrew by turning counterclockwise until it releases.
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After adjustments, push the crown in and screw it down firmly to maintain water resistance.
Push-Pull Crown
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Simply pull gently to switch positions.
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Always push back fully after use.
Crown Positions
Since the NH38/NH70 is a no-date movement, crown operation is simple.
| Position | Function | Notes |
|---|---|---|
| 0 (unscrewed) | Watch running; manual winding available | Unscrew by turning anti-clockwise |
| 1 (fully pulled) | Time setting; hacking stops the seconds | For accurate time setting |
There is no date-setting position on the NH38.
Setting the Time
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Pull the crown to Position 1.
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Rotate to set the time.
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Push the crown back to Position 0 (and screw it down if applicable).
No date means:
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No AM/PM checking
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No danger window
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No risk of damaging calendar gears
Water Resistance
Water resistance depends on your specific case and crown.
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Screw-down crowns generally offer higher water resistance.
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Push-pull crowns are suitable for daily wear but not submersion.
Avoid:
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Hot water or steam rooms
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High humidity with unscrewed crown
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Pressurized water exposure
Heat and steam can compromise gasket seals.
Maintenance & Care
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Store face-up in a cool, dry environment.
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Keep away from magnetic devices (speakers, laptops, phones).
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Service the movement every 3–5 years for lubrication and accuracy.
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After any hard impact, the rotor or balance assembly may need inspection.
Summary of Best Practices
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If unworn for 24+ hours, manually wind before use.
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Avoid magnets and unnecessary moisture.
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Always secure the crown properly.
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No date = no setting risks — enjoy simpler operation.
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Treat the movement with care; it’s a precision mechanical mechanism.
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