Hattori SII Caliber VD51B

Manufacturer	Hattori aka Seiko Instruments Inc. (SII)
Caliber Number	VD51B
Type	Quartz
Lignes	12 3/4”’
Diameter	29.5mm x 26mm (smaller between 3:00-9:00)
Casing Diameter	28.8mm
Thickness	4.57mm
Battery Cell	371 (SR920SW)
Battery Life	~3 years
Frequency	32,768 Hz
Quartz Type	Tuning fork type quartz crystal
Stem	351177 / tap 10
Hand Sizes	1.10mm / 0.65mm / 0.20mm / 0.21mm x 2
Jewels	0
Hacking?	Yes
Anti-Magnetic	> 1600 A/m
Functions	Hours, minutes, central seconds, 1/1 chronograph seconds subdial at 12:00, 60 minutes subdial at 6:00, date at 3:00
Country of Manufacture	Japan
Known Models	AVI-8 Bulman (Too many to list, please add your watch to the comments below…)

The Seiko Instruments (SII) caliber VD51B is a quartz chronograph movement. Something to note about this watch movement is that the chronograph second hand is located in a subdial at 6:00. The central second hand is the running second hand.

Chronograph Sequence:

The chrono sequence on the VD51B is the same as most chronograph watches:

• Start – top button
• Stop – top button
• Reset – bottom button

How to reset the chronograph hand to 0:

If your chronograph second hand isn’t lining up, you can adjust it back to zero by pulling the crown out to time setting position (position 1) and using the chronograph pushers to advance the hand line up at the 60 (or zero/12:00 position). The top button will make the hand go backwards, the bottom button will make it move forward.

Holding the buttons in for more than a second will make the chrono second hand move rapidly, this is also how you get the 60 minute counter hand to line up. For example, if your 60 minute counter is resetting to the 5 minutes mark instead of the 60, you would pull the crown out to position 1, and hold the top button in while the chrono second hand spins around quickly and the 60 minute hand slowly goes back to the position you want it in. Then, be sure to line up the chrono second hand again and push the crown back to position 0.

Battery Replacement

A new battery in the SII caliber VD51B should last approximately 3 years. If you need to change the battery, it is possible to DIY. After replacing or reinstalling the battery cell, you will need to perform a short-circuit procedure by touching one side of your tweezers in the AC terminal (marked AC with an arrow) on the movement and the other on the battery.

Crown/Stem Removal

Look for the hole with “Push” and an up arrow. Using your tweezers or a toothpick, push the lever while pulling out the stem.

Accuracy

SII/TMI claims the caliber VD51B has an accuracy rating of less than +/- 20 when the watch is operating in the normal temperature range from -5 degrees C to +/- 50 degrees C.

VD51A, VD51B, VD51C

The current spec sheets for the VD51 list up to a VD51C variation with a revision date of January 20, 2017. We are still looking into the differences between the A, B, C variations, but it’s likely that they are small updates. If you know, please comment below. In the meantime, this post will be updated when we learn more.

Replacement Price

At the time of this post, replacement prices for the caliber spec VD51B were found online in the range of $17.55 – 24.99 USD.

Technical Drawings

SII VS TMI VS Hatori

You might find this caliber listed as being produced by Hattori aka Epson aka TMI (Time Module Inc) aka Seiko Instruments Inc. We’re not sure why all the different names, but sure they all lead back to Seiko. Read more here

From Wikipedia:

Seiko Holdings Corporation (SEIKO) delegates a large portion of the manufacturing in its watch business to SII and EPSON. Most of watches manufactured by SII are sold through the Seiko Watch Corporation, a subsidiary of Seiko Holdings Corporation. In recent years Seiko Instruments has tried to establish its own marketing channel and brands – Sizukuishi Watch, appetime, J.SPRINGS, ISSEY MIYAKE, tsumori chisato, ALESSI, cacharel, etc.

On January 26, 2009, Seiko Instruments and Seiko Holdings announced that the two companies will be merged on October 1, 2009 through a share swap. Seiko Instruments became a wholly owned subsidiary of Seiko Holdings on October 1, 2009.

Examples of watches with caliber VD51B

The example below was found in this AVI-8 Hawker Hurricane watch.

Additional Resources

• TMI caliber VD51B tech sheets

Please share your SII caliber VD51B experiences with the community below…