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

  • The NH38/NH70 winds naturally whenever you move your wrist.

  • Wearing the watch for 8+ hours per day will typically keep it fully charged.

  • A full wind gives approximately 41 hours of power reserve.

2. Manual Winding

If the watch stops or hasn’t been worn recently:

  1. Make sure the crown is in Position 0 (fully pushed-in or screwed down).

  2. unscrew the crown (twist anti clockwise)

  3. 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.

  • Unscrew by turning counterclockwise until it releases.

  • After adjustments, push the crown in and screw it down firmly to maintain water resistance.

Push-Pull Crown

  • Simply pull gently to switch positions.

  • 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

  1. Pull the crown to Position 1.

  2. Rotate to set the time.

  3. Push the crown back to Position 0 (and screw it down if applicable).

No date means:

  • No AM/PM checking

  • No danger window

  • No risk of damaging calendar gears

Water Resistance

Water resistance depends on your specific case and crown.

  • Screw-down crowns generally offer higher water resistance.

  • Push-pull crowns are suitable for daily wear but not submersion.

Avoid:

  • Hot water or steam rooms

  • High humidity with unscrewed crown

  • Pressurized water exposure

Heat and steam can compromise gasket seals.

Maintenance & Care

  • Store face-up in a cool, dry environment.

  • Keep away from magnetic devices (speakers, laptops, phones).

  • Service the movement every 3–5 years for lubrication and accuracy.

  • After any hard impact, the rotor or balance assembly may need inspection.

Summary of Best Practices

  • If unworn for 24+ hours, manually wind before use.

  • Avoid magnets and unnecessary moisture.

  • Always secure the crown properly.

  • No date = no setting risks — enjoy simpler operation.

  • Treat the movement with care; it’s a precision mechanical mechanism.