Cc Bg 1920 1280
Seiko Caliber 8T63

Seiko Caliber 8T63

Manufacturer Seiko
Caliber Number 8T63, 8T63A
Type Quartz, Mechaquartz
Lignes 13.5”’
Casing Diameter
Battery Cell Number SR936SW (394)
Battery Life
~3 years
Quartz Type Tuning fork type quartz crystal
32,768 Hz (cycles per second)
Driving System
2 part step motor
Hacking Seconds?
Hand Count
Functions Central hours, central minutes, small seconds at 6:00, 24 hour (military time) indicator at 3:00, 60 minute chronograph counter, date at 4:30
Country of Manufacture Japan
Known Models (Please add your watch in the comments below…)

The Seiko caliber 8T63 (actually marked 8T63A) is found in some Seiko branded watches. This mechaquartz chronograph movement is made in Japan and has zero (0) jewels. This movement has been produced by Seiko since at least 2015.

This movement is essentially the Seiko only version of the VK63. When used in Seiko watches, it may be signed with Seiko Time Corp. When found in non-Seiko watches, the VKXX will usually be signed with SII (Seiko Instruments).

8T63, 8T63A, 8T63B, etc:

8T63 is the base caliber number. The trailing letter is the version. 8T63A is the first version, therefore, 8T63 and 8T63A are the same. If there are any future updates to this caliber, the letter will change to 8T63B and so on.

Seiko 8T63 VS 8T68:

There is a similar caliber 8T68 that shares the same functionality as the 8T63. When comparing these two movements, the main difference between them is that the 8T63 shown here has the subdials at 3:00, 6:00, and 9:00. The 8T68 places the subdials at 2:00, 6:00, and 10:00. Both calibers offer a date feature between 4:00 and 5:00.

8T63 Vs 6T63:

The 8T63 is based on the older Seiko caliber 6T63. The functionality and layout on the 8T63 are similar to the 6T63, but this caliber has been updated to provide higher accuracy and better battery life.

Chronograph Functionality:

The 8T63 has a central stopwatch chronograph hand and a 60 minute totalizer at 9:00. The chronograph is only capable of counting up to 60 minutes in one second intervals. It automatically stops after reaching 60 minutes.

Operating the chronograph is similar to many chronograph watches:

  • Button A (top button) – Start
  • Button A (top button) – Stop
  • Button B (bottom button) – Reset

Resetting the Chronograph Hand to Zero:

The Seiko 8T63 is a mechaquartz movement, so the recalibration is not the same as a regular quartz chronograph since the hands are actually mechanically driven. This is one of the drawbacks of a meca-quartz movement, and if the hands are dramatically misaligned, you may need to have your watchmaker pull them off and install them again in the correct position.

After a battery change, you can try the following instructions for lining up the hands (needs confirmed):

  • When the small seconds hand on the 6:00 subdial reaches 12:00, pull the crown out to position 2 (2 clicks to time-setting mode).
  • Press the bottom pusher (button B) for 2+ seconds until the central chronograph hand turns around the dial.
  • Press the crown back in.

For chronograph troubleshooting, see the following:

Seiko Caliber 8t63 Troubleshooting

Battery Life:

In the manual, Seiko claims that a new battery installed in the caliber 8T63 should last approximately 3 years. Keep in mind that the battery will drain faster if you leave the chronograph second hand running – specifically if the chronograph is used for more than 1 hour per day.

There is also a low battery indicator which will cause the small second hand to jump every 2 seconds. The time on your watch will maintain accuracy even in low battery mode.

After replacing the battery, you will need to perform an AC reset. After an AC reset, the second hand may skip 2 seconds for the first 10 seconds.

Seiko Caliber 8t63 Ac Reset

The original battery in the watch was also made in Japan by Seiko. The size is SR936SW which should convert to a 394 cell.


Seiko claims that the caliber 8T63 will maintain accuracy of +/- 15 seconds per month at normal operating temperatures about 41F to 95F while on the wrist.

Replacement Price:

At the time of this post, replacement prices of the 8T63 were found online in the range of $27.50 to 43.00 USD.

The 8T63 in Seiko’s Own Words:

Cal. 8T63A has a new structure employing one crown and two buttons. The construction of chronograph mechanism is based on Cal. 8R28 mechanical chronograph watch by using the one-piece 3 pointed reset hammer. While other Swiss-made watches are using separate hammers which require an assembly and adjustment of the hammers, the one-piece hammer design realizes maximum durability and stability of the component and easier maintenance. It is also equipped with the self-alignment function for all counting hands to return to zero positions instantaneously.” –source

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What is a Meca-Quartz Movement? Watch Movement | Caliber Corner
2 years ago

[…] Seiko 8T63 […]

Seiko Caliber 8T68 Watch Movement | Caliber Corner
2 years ago

[…] is a similar caliber 8T63 that shares the same functionality as the 8T68. When comparing these two movements, the main […]

Joseph hawkins
Joseph hawkins
2 years ago


Ian Watson
Ian Watson
2 years ago
Reply to  Joseph hawkins

You will prob end up like I did and buying in a couple cheap or not working Pulsar ones and harvest the parts from there. On some of the VK63 Pulsar’s they have unique aluminium cap buttons which are insanely hard to find loose and the Pulsar’s do come up more often these days with problems or for spares.

Ian Watson
Ian Watson
2 years ago

With the VK63, Seiko/Pulsar state you have to utilise a new flyback set of hands because removal weakens the mounting onto the pivot but they said this but make absolutely NO provision for new hands.

I love my Pulsar VK63’s, seriously nice bit of wrist furniture and the design of these is as a say a rally drivers watch hence why there is only 60 minutes but rally driver navigator’s require instant resetting of the chronograph which this movement is ideal for.

Joseph hawkins
Joseph hawkins
1 year ago

Cant find size of crystal I need for seiko ssb297 1

1 year ago

Great piece but will the watch’s second hand ever move, other than pressing the “A” botton. Thank you

7 months ago
Reply to  Michael

That central seconds hand is the chronograph\stopwatch\timer which is why it starts when you press button A.
The clock seconds are the small dial at 6:00

7 months ago

Based on my experience, I think that the VK63 is based on the older 6T63 as they both have the +/- 20s/month accuracy and no low-battery warning, whereas the 8T63 is +/- 15s and includes the 2-second tick as a low battery warning.

Mike Lima
Mike Lima
6 months ago

24 hour dial just follows the hour hand. You probably can use it as an AM/PM indicator. Wish you could set it independently.

3 months ago
Reply to  Mike Lima

That’s exactly what it’s meant for, an AM/PM indicator so you can set the date correctly. Otherwise, completely useless sub dial which I wish they’d make into something useful like a 30 minute or 12 he chrono timer dial ‍♂️

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