Miyota Caliber 90S5

Manufacturer	Miyota (Citizen)
Caliber Number	90S5
Movement Type	Automatic, self-winding mechanical
Lignes	11.5”’
Diameter	26mm
Thickness	3.90mm
Total Height	5.64mm
Jewel  Count	24 jewels
Beat Rate / Frequency	28,800 bph / 4 Hz
Anti-Shock System	Parashock
Power Reserve	42+ hours
Rotor Direction	Uni-directional (clockwise)
Hand Windable?	Yes
Lift Angle	51 degrees
Stem Part #	065-A05 (tap 10)
Dial Screws	929-808
Case Clamps	082-060
Case Clamp Screws	924-752
Hand Sizes	1.52mm (hrs) / 1.00mm (mins) / 0.17mm (secs)
Hand Count	2
Functions	Central hours; central minutes; central sweeping seconds; open balance wheel dial at 5:00
Hacking Seconds?	Yes
Country of Manufacture	Made in Japan
Known Models	Kurono Toki, Kurono Mori, Kurono Seiji, Kurono 34mm, Lorier Neptune Series IV, Lorier Falcon Series III, Aevig Huldra (Add yours in the comments below…)
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The Miyota caliber 90S5 is a member of 90/91 family of watch movements. This caliber is part of Miyota’s “Premium Automatic” line. It tells the time via a traditional 3 hand display with no date option. The unique design element of this movement is that it has an open-heart (aka open balance wheel) on the dial around the 5:00 position. This movement has 24 jewels and is made in Japan. Sometimes this movement is mistakenly written as “9055”.

Time Setting:

The caliber 90S5 is a no-date movement so the crown only has two positions: winding (position 1) and time adjusting (position 2). The set the time on your 90S5 powered watch, pull the crown out one click to position 2. You may need to unscrew the crown if it is a divers style watch with a screw-down system.

Winding + Power Reserve:

Winding the movement 15-20 clockwise will start the movement. To fully wind the movement, turn the crown 40 times. The power reserve when the movement is fully wound is supposed to be more than 42 hours.

Accuracy:

Miyota claims that the caliber 90S5 offers accuracy of -10 ~ +30 seconds per day. This is measured within 10-60 minutes from a full wind via the crown.

Replacement Prices:

At the time of this post, caliber 90S5 replacement prices were found online in the range of $99.00 – $115.00 USD.

90S5 VS 9029:

There is a similar and more common Miyota caliber 9029. Both are 26mm in diameter, have 24 jewels, both beat at 28,800 vph, and have the same dial feet location. The main difference is that the 9029 is a 2 hand watch without a sweeping second hand. Also, the 90S5 has a decorated gilt front plate that may add to the aesthetics of the open balance feature depending on the dial design.

Usage in Microbrand Watches:

At this time, there are still only a few brands using the Miyota caliber 90S5 in their watches. One interesting example of this is the Kurono Mori and Toki (retail price $1,738 USD). Why this is interesting is because this caliber’s specialty is its “open-heart” on the dial side, however, neither of these watches have a cutout on the dial for a view into the swinging balance wheel. Also, neither model features an exhibition style caseback to see the movement.

Kurono Tokyo’s website says this about their choice of movement:

“For the movement, Hajime chose the calibre 90S5 – Miyota’s highest end movement from its Premium series. Balancing affordability with over-the-top construction quality, the cal.90S5 is made in Japan, features a stop-seconds automatic mechanism with a 42 hour power reserve. Kurono is proudly made in Japan, assembled by hand. ” –Kurono Tokyo

The Miyota caliber 90S5 is part of the 90 series of movements which includes the 9015, 9019, 9039 and 9029. While the 90S5 does feature a greater level of finishing on the dial side with a decorated gilt plate, it is mainly because of the open balance wheel which the Kurono watches does not make use of.

Watch enthusiasts are used to brands using date movements in no-date watches, causing a phantom date mode with a clicking datewheel that serves no purpose, but we’re not used to a watch with an open balance and a solid dial. It seems that Kurono could have simply used the Miyota 9039 which has the exact same specs, no date, and looks identical from the rotor side of the movement – all without an open-heart design.

With the extra finishing and the open balance design, the 90S5 appears to be the highest priced caliber in the 9 series. As mentioned, it is also not found in many watches yet. Perhaps these are part of the reasoning behind the brand’s choice.

Additional Resources:

• Miyota 905S tech drawings (pdf)