Seiko Caliber Nh71a Drawings

Seiko (SII) Caliber NH71A

Seiko Caliber Nh71a Drawings

Manufacturer Seiko (aka Seiko Instruments, SII)
Caliber Number NH71 (aka NH71A)
Movement Type Automatic
Lignes
12”’
Diameter
27.4mm
Casing Diameter
27mm
Height
5.32mm thick
Jewels 24
Vibrations Per Hour
21,600 bph (3Hz) (6 beats per second)
Lift Angle 53 degrees
Shock System Diashock
Power Reserve
~41 hours
Winding Direction
Bi-directional (Magic Lever)
Hacking? Yes
Hand-Windable? Yes
Functions Hours, minutes, central seconds
Country of Manufacture Japan/Malaysia
Known Brands
(add your watch in the comments below…)

The Seiko/TMI/SII caliber NH71A is a skeletonized automatic caliber in the NH family of watch movements. This movement is based on the popular NH3 (NH35A) framework therefore is hackable as well as hand-windable.

NH71 / NH71A / NH71B / NH71C:

The general caliber number is NH71, from the NH family of movements, with NH71A being the first version. The subsequent letter variations indicate evolution in the movements development. As of this post, only the NH71A exists, but if there are any upgrades or changes to the movement in the future, the letter will change to NH71B, NH71C, and so on.

NH71 vs NH70:

There is a similar caliber NH70. The NH71 is newer than the NH70. The main difference between these two movements is cosmetic: The NH70 is nickel plated and the NH71 is gold plated (gilt).

Another thing to note about these two calibers is that the NH70 can be made in either Japan or Malaysia, but at the time of this post, the NH71 is only made in Japan.

Accuracy:

In the technical documentation, Time Module claims that the NH71A accuracy range is within -20~+40 seconds per day under normal conditions. They use three measurement positions: Dial up, crown up, crown down.

Note: When you attempt to get a measurement of your watch’s accuracy, it’s important to make sure your watch is fully wound or the lack of power reserve may skew the test results. TMI states that measurements should be done within 10-60 minutes after the movement is fully wound up.

Winding the Mainspring:

So what does fully wound up mean? The NH71A should be fully wound after about 55 manual turns of the crown. This movement is also equipped with the Seiko Magic Lever, so shaking the watch side to side should get it going almost immediately.

Crown Position Functions:

The caliber NH71 has two crown positions (not counting screwing in the crown if your watch is equipped with a screw-down crown):

  • 0 (against the case): Clockwise = Manual Winding / Counterclockwise = Nothing
  • 1 (pulled out one click): Time setting mode

Seiko Caliber Nh71a Instructions

Hacking:

Since the NH71A is based on the NH35A, that means it has hacking functionality. A hackable watch is one that stops the second hand from advancing forward when the crown is pulled out to time setting mode. Seiko officially refers to this hacking function as a “second hand reset” and the hacking mechanism as a “balance stop lever”.

Rotor Variations:

Some watch brands using the NH70A will opt for a custom rotor, but according to official tech sheets, two stock rotors are available depending on the country of origin: Japan or Malaysia. Regardless of origin, the stock Seiko rotor has Côtes de Genève finishing.

Replacement Prices:

At the time of this post, replacement prices for the caliber NH35A were found online in the range of $40-55 USD.

Tech Drawing:

Seiko Caliber Nh71a Drawing Dial Side

Additional Resources:

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9 Comments
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Vlad
Vlad
3 years ago

I want a watch with this movement so bad but I can’t find anything. Any recommendations?

Thomas
Thomas
2 years ago
Reply to  Vlad

Undone Sometsuko if you’re quick.

FrankyFrancesco
FrankyFrancesco
2 years ago
Reply to  Vlad

I make custom watches. My latest is a turtle build with NH70 movement. Check my IG frankybassfrancesco thanks, im located in beautiful west oakland, CA USA.

Dan
Dan
1 year ago

i just received one for a build and it doesn’t appear to be running, nor can I wind it until it stops winding

Dan
Dan
1 year ago

Never mind. I was being too nice to it. Had to push harder to sit the crown stem all the way in.

trackback
Seiko (SII) Caliber NH72 Watch Movement | Caliber Corner
1 year ago

[…] it is part of the NH7X series of skeleton dial movements, starting with the NH70 (silver) and NH71 (gilt gold tone). Official technical documents for this series were updated in June 2022, also […]

trackback
List of Seiko Watch Movements Watch Movement | Caliber Corner
1 year ago

[…] NH71A […]

Dan
Dan
1 year ago

i just received one for a build and it doesn’t appear to be running, nor can I wind it until it stops winding

Dan
Dan
1 year ago
Reply to  Dan

Never mind. I was being too nice to it. Had to push harder to sit the crown stem all the way in.

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