Grand Seiko Caliber 9S64

The Grand Seiko caliber 9S64 (9S64A) is handwound mechanical watch movement with 24 jewels. Luxury watches powered by the GS 9S64 have been on the market since this movement was announced at Baselworld 2011.

In Grand Seiko’s own words:

“Caliber 9S64 is a manual winding mechanical movement that achieves a stable level of precision during actual use and a power reserve of approximately three days when fully wound.” –Source

Movement Text:

GS / GRAND SEIKO / 9S64A / TWENTY-FOUR JEWELS / ADJUSTED TO SIX POSITIONS AND TEMPERATURE / JAPAN / Serial Number / SEIKO TIME CORP. (outer edge of mainplate)

Power Reserve:

The runtime on a fully wound calibre 9S64 powered watch is approximately 72 hours or 3 days in normal conditions.

What is the direction I should wind the watch?

Turn the crown clockwise (forward) to wind the mainspring. Be sure that the crown is unscrewed first (if your watch has a screw-down crown). Wind the crown “slowly” (or just not too fast).

How many winds gets it to full power reserve?

From a complete stop (no energy in the mainspring aka the watch is not ticking), turning the crown about 60 times will get it to maximum power reserve.

Grand Seiko recommends winding your watch every day around the same time, which in that case it would take about 20 winds to replenish the power reserve back to full.

How many winds to get it going?

From a complete stop, do not be alarmed if it takes around 15 winds until you see some action in the seconds hand or balance wheel. As GS explains it:

“When the watch is used from a state in which the mainspring is unwound to a stop, it does not move immediately even if the mainspring is wound with the winding crown. This is because of the mechanical watch’s feature that the mainspring torque (force) is weak at the beginning of mainspring winding. The seconds hand starts moving when the mainspring is wound to reach a certain degree of torque strength, while the watch can be made to move advance by shaking it to rotate the balance wheel forcibly.” – Official 9S64 Operating Instructions, page 30 (link below)

The key to accuracy:

“If the mainspring is not wound up sufficiently, the watch may lose or gain time. To attain a high accuracy, we suggest that the mainspring is wound up fully once a day at a fixed time.” – Official 9S64 Operating Instructions, page 30 (link below)

Overwinding the Mainspring:

The possibility of over-winding the mainspring is a concern for many new 9S64 watch owners. Most modern manual-wind mechanical watches will prevent the user from over-winding the mainspring, a function that presents itself by making the winding experience more firm as it gets closer to fully wound, then stops allowing further winding – going past this point will cause damage.

9S64 owners will be happy to know that Grand Seiko engineered this caliber to be able to handle continuous winding of the crown, even after the mainspring has reached full capacity. This is thanks to a built-in clutch system that allows “overwinding” without breaking anything. This feature is nice because it gives the wearer confidence that the watch at it’s maximum power reserve (nice for testing purposes).

“Generally speaking, the crown of the manual winding mechanical watch cannot be turned further when it is wound up fully. However, the crown of the Cal. 9S64 and 9S63 can be turned endlessly even after the watch is fully wound up. If you keep turning the crown, that gives no effect to winding, but the watch is so designed as to make the winding a little tighter and not to damage the watch. However, please refrain from excessive operation.” – Official 9S64 Operating Instructions, page 30 (link below)

What does it feel like?

You still may feel some resistance, due to the spring being fully wound, but it is supposed to be able to handle further winding without breaking. As Grand Seiko advises above, don’t do this often. If you have a 9S64 powered watch, please describe your winding experience and over-winding prevention or hard stop feeling when interacting with your watch.

Additional Resources:

• Official operating instructions (pdf)
• Grand Seiko 9S page
• List of Seiko movements