Seiko Caliber 5R66

Seiko caliber 5R66 is a Spring Drive movement with a GMT hand and power reserve indicator. This movement is made in Japan and has 30 jewels with a power reserve of 70 hours.

Accuracy:

According to Seiko official documentation, they claim that this movement has an accuracy rating of +/- 15 seconds per month in normal operating conditions and temperatures (-10 ~ +60 degrees C). The daily rate is listed as +/- 1 second per day.

Power Reserve:

The caliber 5R66 has a power reserve of 70 hours. Once the mainspring is fully wound, it cannot be over-wound thanks to a slipping mechanism that prevents the mainspring from over-winding. Watches with this caliber typically have a power reserve indicator on the dial.

How long does it take to fully wind when wearing the watch?

According to Seiko:

“The mainspring of the watch becomes fully wound when it is worn for twelve hours for three to five consecutive days. In a case where you wear the watch for a short period of time each day, observe the power reserve indicator to check the level of the remaining power. If necessary, manually wind the mainspring.”

When manual winding, rotating the crown 5 times can garner about 10 hours of power reserve.

Smoothness:

This Spring Drive automatic movement is most notable for it’s super smooth Glide-Motion second hand. You can see it up-close in action here.

5R66 VS 5R65:

There is a similar Seiko caliber 5R65 with the main difference being that it does not have a 24 hour hand – that is the only difference.

How to Set the Time:

The crown on the 5R66 has 3 positions:

• Position 0 – Manual winding
• Position 1 –  Local hours and Date setting mode
• Position 2 – Time setting mode

Although Seiko documentation refers to the fourth hand on the 5R66 simply as a 24 hour hand, it is also a GMT hand capable of tracking time in a second time zone. Because the main hours hand can be adjusted independently, this is what would be referred to as a traveler GMT or “true” GMT.

The reason why it is important to distinguish a GMT hand from a 24 hour hand is because some watches have a 24 hour hand which cannot be adjusted separately from the main hour hand – making it a 24 hour indicator to tell military time or day/night. The 5R66, however, can be adjusted independently to keep track of dual time-zones.

To set the time, pull the crown out two clicks to position 2 and rotate the crown until the GMT hand and minutes are set to the desired time.

Next, put the crown in position 1 (pulled out one click) and rotate the crown forwards or backwards to adjust the main hour hand (12 hour hand). This motion will also adjust the date when advancing the hand every 24 times. According to Seiko, you should adjust the independent hour hand so that it moves in one-hour increments. If the other hands move slightly while adjusting the hour hand, it’s ok.

The 5R66 has hacking seconds with the crown in position 2. The seconds do not hack in position 1, allowing for quick local time adjustment without disrupting the timekeeping already set on the watch (for example, when jumping time zones or adjusting for daylight savings time).

Service/Repair:

At the time of this post, Seiko calls for all repairs and overhauls to be sent to Seiko Watch Company in Japan for service. They will not provide any movement parts to watchmakers.

Here is a service price list.

Resources:

• All about the Seiko Spring Drive
• Caliber 5R66 official manual

Note: a photo of this movement is desperately needed to complete this listing. If you have an original photo that can be posted, please let us know.