Seiko Caliber 6R55

Manufacturer	Seiko
Caliber Number	6R55, 6R55A
Movement Type	Automatic, self-winding mechanical
In-House?	Yes
Diameter	(needs confirmed)
Casing Diameter	(needs confirmed)
Height	(needs confirmed)
Jewels	24
Vibrations Per Hour	21,600 bph, 3Hz
Lift Angle	53 degrees
Shock System?	Diashock
Mainspring	Spron 510
Regulation	ETACHRON
Power Reserve	~72 hours (3 days)
Rotor Direction	Bi-directional (Magic Lever)
Hand-Windable?	Yes
Magnetic Resistance	4,800 A/m (60 gauss)
Functions	Central hours; central minutes; central sweeping second hand; date at 3:00
Hacking Seconds?	Yes
Country of Manufacture	Japan
Known Models	King Seiko models: SPB369, SPB371, SPB373 (Add more in the comments below)

The Seiko caliber 6R55 is an automatic movement found in larger 39mm King Seiko that was introduced on February 8, 2023. This movement uses the framework of what Seiko refers to as the “high performance” 6R series calibers. The 6R55 is considered to be an upgrade from the caliber 6R35 (although not significant).

In Seiko’s own words:

“The 39mm size uses the new Caliber 6R55, which comes with an increased power reserve of three full days (72 hours) as indicated on the six o’clock position of the dial. All three watches join the main King Seiko collection and will be available from April 2023 at select Seiko retailers nationwide.” –source

6R55 VS 6R31:

With the announcement of the new brown dial King Seiko Watchmaking 110th Anniversary Limited Edition (SPB365) watch at the same time as the new larger King Seiko models, there may be some confusion around the calibres within. The anniversary edition is a 37mm with the cal. 6R31 that is found in the other 37mm models released in 2021. The new King Seiko Automatic 3 Days are powered by the caliber 6R55 being discussed on this page.

The biggest difference between the two movements is that the 6R31 is a no-date and the 6R55 has a calendar complication with a date window at 3:00. There also appears to be a 2 hour increase in power reserve. The 6R31 has a power reserve of approximately 70 hours and the 6R55 has a power reserve of approximately 72 hours. Although the movement linge size or diameter has not been confirmed, that may be another difference between the two calibers. The 6R31 is found in King Seiko models from the initial 2021 relaunch. Those models measured 37mm diameter and 12.1mm thick. The new 2023 King Seiko with the 6R55 measures 39mm and 11.9mm thick.

Furthermore, the 6R31 has a silver tone rotor, whereas the 6R55 appears to have a gold tone rotor (based on early press images released by Seiko).

Editor’s Gripe (OT): As with most watch brands charging thousands of dollars for their watches, Seiko doesn’t bother to show the caseback on their King Seiko 39 product pages, so who knows! Apparently you’re supposed to make all of your buying decisions based on blog articles, hype, and a single picture of the dial/front of the case. Doesn’t it feel like brands that present watches like this do not respect the collectors and their hard earned money? What happened to the concept of seeing what you’re getting before you buy it? From dark and blurry cell phone pics on eBay to century old watch manufacturers showing one computer generated stock image, it leaves a lot to be questioned. If you appreciate seeing many angles of watches before you buy, you’ll like my other site!

6R55 / 6R55A / 6R55B:

This is still a rather new movement, so currently there is only the 6R55A. The general caliber number is 6R55, with 6R55A being the first version. The subsequent letter variations indicate evolution stages in the movements development. This post will be updated if the movement gets any upgrades.

Accuracy of the 6R55:

Seiko claims the accuracy of the caliber 6R55 has a rating of -15/+25 seconds per day in normal temperature conditions (between 5 – 35 degrees C).

Seiko says this about accuracy:

• The accuracy of mechanical watches may not fall within the specified range of time accuracy because of loss/gain changes due to the conditions of use, such as the length of time during which the watch is worn on the wrist, arm movement, whether the mainspring is wound up fully or not, etc.
• The key components in mechanical watches are made of metals which expand or contract depending on temperatures due to metal properties. This exerts an effect on the accuracy of the watches. Mechanical watches tend to lose time at high temperatures while they tend to gain time at low temperatures.
• In order to improve accuracy, it is important to regularly supply energy to the balance that controls the speed of the gears. The driving force of the mainspring that powers mechanical watches varies between when it is fully wound and immediately before it is unwound. As the mainspring unwinds, the force weakens.
• Relatively steady accuracy can be obtained by wearing the watch on the wrist frequently for the self-winding type and winding up the mainspring fully everyday at a fixed time to move it regularly for the wind-up mechanical type.
• When affected by external strong magnetism, a mechanical watch may loss/gain time temporarily. The parts of the watch may become magnetized depending on the extent of the effect. In such a case, consult the retailer from whom the watch was purchased since the watch requires repair, including demagnetizing.

Power Reserve:

The caliber 6R55 holds a power reserve of at least 72 hours. To fully wind the mainspring, turn the crown a minimum of 55 times.

Crown Position Functions:

0 (against the case): Clockwise = Manual Winding / Counterclockwise = Nothing
1 (pulled out one click): Clockwise = Nothing / Counterclockwise = Date setting
2 (pulled out two clicks): Time setting clockwise and counterclockwise

Can you overwind the movement?

No. According to the Seiko documentation, manually winding the movement after it is already fully wound will not break the spring.

When can you adjust the date?

Do not adjust the date between 9:00 PM and 1:00 AM.

Stem Removal:

To remove the stem, make sure the crown is in position 0 or normal position (not date or time setting position). There is a lever with a small indentation for your tool. Gently press down while pulling the stem out. See official instructions below for more guidance:

How often does the 6R55 need serviced?

According to official Seiko documentation, watches with the caliber 6R55 should be serviced every 2-3 years. Learn all about Seiko service intervals here. At the time of this post, the starting cost of getting this movement overhauled by Seiko is $260.00 USD.

Examples of watches with caliber 6R55:

Additional Resources:

• Seiko King Seiko official announcement (February 8, 2023)
• Seiko 6R55 official instruction manual (pdf)