Watch WinderSeiko · Seiko 6R31
King Seiko SPB279, Garyu-Bai and the 37 mm KSK: inside the 6R31
The 37 mm King Seiko KSK models, including the SPB279, SPB283 and the red-dial SPB287 "Garyu-Bai", run on the no-date 6R31. From a full wind it runs about 70 hours, or nearly three days.
Watches that use the Seiko 6R31
The 6R31 is the no-date version of Seiko's 6R35, and its best-known home is the King Seiko collection Seiko relaunched in 2022. The 1965 King Seiko KSK had no date window, so Seiko chose a no-date movement to keep the dial clean. If your King Seiko is 37 mm with no date, it very likely has a 6R31 inside. It's a smaller list than the 6R35's, because Seiko uses the 6R31 far less often.
| Watch | Example references | Notes |
|---|---|---|
| King Seiko KSK (37 mm) | SPB279 (silver sunburst), SPB281 (light grey, vertical brushing) | The core 2022 relaunch. 37 mm, 12.1 mm thick, 100 m, box sapphire crystal. |
| King Seiko KSK (37 mm) | SPB283 (charcoal), SPB285 (brown) | Same case and movement, different dials. |
| King Seiko "Garyu-Bai" | SPB287 | Burgundy sunburst dial named after a famous plum tree in Kameido, where the Daini Seikosha factory stood. |
| King Seiko 110th anniversary edition | SPB365 | 2023 limited edition of 1,200 in the 37 mm case, with the 6R31. |
Two King Seikos are easy to confuse with these. The 39 mm King Seiko SPB369, SPB371 and SPB373 from 2023 add a date and use the 72-hour 6R55. The 2021 limited KSK re-creation, the SJE083, uses the thinner 4 Hz 6L35. The case back or Seiko's spec sheet tells you which you have.
Specs at a glance
| Type | Automatic, hacking, hand-winding |
|---|---|
| Frequency | 21,600 vph (3 Hz) |
| Jewels | 24 |
| Power reserve | About 70 hours |
| Rated accuracy | +25 to -15 s/day, worn on the wrist between 5°C and 35°C |
| Base / derived from | The Seiko 6R35 without the date mechanism; the 6R35 itself descends from the 6R15 |
| Complications | None: hours, minutes and central seconds only |
| Magnetic resistance | 4,800 A/m (as listed for the King Seiko collection) |
History and where it came from
King Seiko began in the 1960s at Daini Seikosha, one of Seiko's two watchmaking companies, as a rival to Suwa Seikosha's Grand Seiko. The 1965 KSK, with its sharp faceted case and no-date dial, is the design everyone remembers. The line faded through the late 1970s and was discontinued in the early 1980s, according to aBlogtoWatch.
Seiko tested the waters in 2021 with the SJE083, a limited re-creation of the KSK on the 6L35. In January 2022 it announced a permanent King Seiko collection: five 37 mm watches, available from February 2022, all using the 6R31. Seiko's announcement lists 24 jewels, 21,600 vibrations per hour and a 70-hour reserve.
Mechanically, the 6R31 is nothing exotic. Seiko's instruction manual covers the 6R31, 6R35 and 6R38 together, with identical accuracy, winding and reserve specs; the only difference listed is that the 6R35 shows a date. Monochrome describes the 6R31 as having the same architecture as the 6R35 minus the date. That lineage runs back through the 6R15 to Seiko's 2000s mid-range automatics.
The choice drew some criticism. The original King Seikos became known for high-beat movements at 28,800 or even 36,000 vibrations per hour, and aBlogtoWatch pointed out that the 3 Hz 6R31 gives a choppier seconds sweep than those did. Seiko's answer was the price: the 6R31 kept the KSK line well below Grand Seiko.
Accuracy in the real world
Seiko rates the 6R31 at +25 to -15 seconds a day when worn on the wrist between 5°C and 35°C, the same as the 6R35. That's the rating you'll also find on a Seiko Alpinist, which some buyers find disappointing on a watch named King Seiko.
In practice most examples do much better than the limits. Seiko's technical guide for the 6R35, the dated twin, sets factory tests of ±10 seconds a day dial-up and ±15 in two vertical positions, and owners of 6R-powered Seikos commonly report 5 to 10 seconds a day. Treat that as typical, not guaranteed: there's variation between examples, and a watchmaker can regulate one that lands near the edge.
The rate shifts with resting position, so owners often trim the daily average by choosing whether the watch sits dial-up or crown-down overnight.
Reliability and servicing
There's no known pattern of faults. The 6R31 shares its design and nearly all its parts with the 6R35, which Seiko uses across much of the Prospex and Presage ranges, so parts availability and watchmaker familiarity should be good for years.
- Service. Seiko service centres handle it routinely. Independents who know the 6R35 can service it too.
- Regulation. It uses Seiko's conventional Etachron regulator, so adjusting the rate is quick for any competent watchmaker.
- No date to break. Without a date mechanism there's one less thing to go wrong and no date-change danger zone.
Quirks worth knowing
- Simpler crown. With no date, there's no quickset position. Pull the crown out once to set the time (the seconds hand stops), and wind it in the pushed-in position.
- 3 Hz sweep. At six beats a second, the seconds hand moves in visible steps compared with a 4 Hz or high-beat movement. On a dress watch like the SPB279 you may notice it.
- Long wind from stopped. Seventy hours is a lot of mainspring. Give it 30 to 40 turns of the crown after it stops rather than hoping wear will fill it.
How it compares
- Seiko 6R35: the same movement with a date, in the SPB143, Alpinist and Sumo. Pick based on the watch, not the calibre.
- Seiko 6L35: the thinner, 4 Hz movement in the SJE083 KSK re-creation. Smoother sweep, but only about 45 hours.
- Grand Seiko 9S65: the next step up, with a 4 Hz beat, 72 hours and much tighter regulation, at several times the price.
- Powermatic 80: the Swiss alternative in the Tissot PRX and Gentleman, with 80 hours at 3 Hz. Harder to get serviced independently.
- Nomos Alpha: a hand-wound no-date dress movement in the Nomos Tangente and Orion, with about 43 hours. You wind it every day or two.
Living with the 70-hour reserve
A dress-leaning watch like a King Seiko often isn't worn every day, which is where 70 hours earns its keep. Wear your SPB279 to dinner on Friday, take it off at 11pm, and if it was fully wound it's still running until about 9pm on Monday. Pick it up for work on Monday morning and the time is still correct.
The weak spot is a spring that was never full. If the Garyu-Bai spent its week in the drawer and you wore it for one evening, it has only a few hours of charge. The fix is simple: give it 30 or 40 turns of the crown before you put it on, and it will carry you through the weekend. With no date, a stopped 6R31 is only a quick time reset, but it's still easier not to let it stop.
If the King Seiko is one of several watches you rotate, Watch Winder counts down its 70-hour reserve, alongside each watch you own, and reminds you before it stops. For a one-off check on a trip or long weekend, use the "Will my watch stop?" calculator.
Verdict
The 6R31 is a sensible, unglamorous choice for the King Seiko revival. It gives the SPB279, the Garyu-Bai and the rest of the 37 mm KSK line a near-three-day reserve, hacking, hand-winding and easy servicing, and it keeps the dial free of a date window as the 1965 original was. What it doesn't give you is the high-beat smoothness or tight regulation the King Seiko name once stood for. If that matters, look at the 6L35 re-creation or Grand Seiko; if you want a beautifully finished everyday watch, the 6R31 does its job well.
FAQ
How long does a King Seiko SPB279 run off the wrist?
A fully wound SPB279 runs about 70 hours, just under three days. That's enough to take it off on Friday evening and find it running on Monday.
What movement is in the King Seiko Garyu-Bai SPB287?
The SPB287 Garyu-Bai uses Seiko's calibre 6R31, a 24-jewel automatic with a 70-hour reserve and no date.
How accurate is the King Seiko SPB281?
Seiko rates its 6R31 at +25 to -15 seconds a day when worn. Many examples do better, and a watchmaker can regulate one that runs near the limits.
Does the King Seiko KSK hack and hand-wind?
Yes. The 6R31 in the 37 mm King Seiko stops the seconds hand when you pull the crown to set the time, and the crown winds the mainspring.
What is the difference between the 6R31 and the 6R35?
The 6R31 has no date. Seiko lists the same beat rate, jewels, accuracy rating and 70-hour reserve for both.
Why doesn't the King Seiko SPB279 have a date?
It follows the 1965 King Seiko KSK, which had no date. The no-date 6R31 lets Seiko keep that clean dial layout.
Do the 39 mm King Seiko models use the 6R31?
No. The 39 mm SPB369, SPB371 and SPB373 have a date and use the 6R55, which runs for about 72 hours.
Sources
- Seiko: The King Seiko Collection returns (2022 announcement)
- Seiko: Cal. 6R31/6R35/6R38 instructions
- Monochrome: 2022 King Seiko collection SPB279 to SPB287 hands-on
- aBlogtoWatch: Seiko restores the King Seiko collection with five new watches
- Monochrome: King Seiko 39mm date collection SPB369, SPB371, SPB373
Keeping it running
- On an average day an automatic gains roughly 4 hours of reserve per hour on the wrist, so about 18 hours of wear fills the Seiko 6R31. Desk days charge more slowly.
- Most automatics can also be wound by the crown. If yours has stopped, a few dozen turns gets it going before you put it on.
- Off the wrist it stops about 70 hours after it was last full. Stopped sooner?
- On a watch winder, start at about 650 turns per day, both directions. Winder settings for every movement.
- If it does stop, don't set the date between 9pm and 3am. Check if it's safe.
All Seiko movements · Other 70-hour movements
Never let it stop
Watch Winder counts down the reserve of every watch you own and reminds you before one stops. It already knows the Seiko 6R31: type your watch's name and the reserve fills itself in.
Manufacturer's published figure. Real reserve varies with the watch's age and service; check your manual.