Seiko · Seiko 4R39

Seiko Presage Style60's and Zen Garden power reserve: inside the 4R39

The open-heart Seiko Presage Style60's (SSA425) and the Japanese Garden models (SSA421, SSA464) run on Seiko's 4R39, with a 24-hour hand beside the open heart. From a full wind it runs about 41 hours, or 1.7 days.

Updated September 2026 · Based on manufacturer specs, published reviews and watchmaker/owner reports

Watches that use the Seiko 4R39

If your Seiko Presage has an open heart at 9 o'clock showing the balance, a small 24-hour subdial above it, and no date, it has a 4R39. It's the open-heart 4R38 with a 24-hour hand added. It isn't a GMT: the 24-hour hand is locked to the main hour hand and simply shows whether it's day or night. Today it's in the open-heart Presage Style60's and the Japanese Garden series. It started out in Seiko's Premier line.

Specs at a glance

History and where it came from

Seiko covers the 4R38A and 4R39A in a single technical guide and says both were developed from the 4R36A, the day-date movement in the Seiko 5 Sports and Turtle. Seiko removed the calendar and gold-plated the balance, which shows through the dial at 9 o'clock. On the 4R39 it added a 24-hour wheel and an intermediate wheel under the dial, driving a hand in a small subdial. Everything else is the same as the rest of the 4R family: the 27.4 mm footprint, the 24 jewels, the escapement and the 41-hour mainspring.

Reference sites date the 4R39 to around 2011, when it appeared in Seiko's Premier Automatic line. There were two series, 2011 to 2013 and 2014 to 2018. Later, the 4R39 moved into Presage. It's now in the open-heart versions of the Style60's, which Seiko styled after its 1964 Crown Chronograph, and in the Japanese Garden series, whose dials are inspired by raked gravel and sand patterns.

Accuracy in the real world

Seiko rates the 4R39 at +45 to -35 seconds a day on the wrist, the same as every other 4R. Its service guide sets tighter workshop limits: within ±20 s/day dial-up when fully wound, and within ±30 s/day in the vertical positions and after 24 hours of running down. Some retailer listings quote other figures, but Seiko's own manual gives +45/-35.

The balance and escapement are the same as in the 4R35 and 4R36, and the extra 24-hour wheel adds very little load. So you can expect a Style60's SSA425 or Zen Garden SSA421 to keep time much like any 4R Seiko. Owners of these movements commonly report something between a few seconds and 20 seconds a day fast, with some near zero and a few near the edge of the spec. It has a conventional regulator arm, so a watchmaker can bring it closer quickly and cheaply.

Reliability and servicing

There's no known weakness specific to the 4R39. It's built from well-proven 4R parts, with Seiko's Diashock shock protection and Magic Lever automatic winding. Seiko service centres handle it, and independents who know Seiko movements can service it too.

Replacing the movement is less simple than on a date-only Seiko. The open heart has to line up with the dial cutout and the 24-hour hand needs its own wheel, so a common NH35 won't drop in. If the movement can't be repaired, you need another 4R39 or a matching open-heart movement with a 24-hour hand.

Quirks worth knowing

• Not a GMT. This is the most common confusion. You can't set the 24-hour hand on its own, so it can't show a second time zone. It moves with the hour hand and tells you whether it's 8am or 8pm. For a true second time zone, look at the NH34 / 4R34 GMT in the Style60's SSK models.
• Set AM/PM with the 24-hour hand. Seiko's manual says to watch the 24-hour hand as you set the time, so the watch is on the right half of the day. On a watch that has stopped, it's the only clue.
• No date, no danger zone. With no calendar, you can set the time at any hour without risking the date mechanism.
• Winding from stopped. The crown only winds clockwise. A stopped 4R39 won't start straight away because the spring has little torque at first, so keep winding until the seconds hand moves.
• Busy dial. An open heart, a subdial and textured Presage dials mean a lot to look at. The 24-hour subdial is small, so it takes a glance to read.

How it compares

• Seiko 4R38: the same open-heart movement without the 24-hour hand, used in the Cocktail Time Open Heart.
• Seiko NH34 / 4R34 GMT: a real GMT with an independently set 24-hour hand and a date, and the same 41-hour reserve. Choose it if you travel.
• Seiko 4R35 / 4R36: the date and day-date versions in the time-and-date Style60's and most other affordable Seikos.
• Seiko 6R5J: Seiko's upmarket open-heart calibre, with a 72-hour reserve that survives a full weekend.

Living with the 41-hour reserve

Forty-one hours doesn't cover a weekend. Take your Style60's SSA425 off at 6pm on Friday and a fully wound 4R39 will stop at about 11am on Sunday. If you only wore it for a morning, it will stop sooner. The open heart makes it easy to spot: if the balance at 9 o'clock isn't moving, it has run down.

Once it has stopped, restarting a 4R39 takes a little more care than a simple three-hander, because you have to get the 24-hour hand on the right half of the day. It's easier to keep it running. Wind it a few dozen turns by the crown on the mornings you pick it, and Watch Winder counts down the 41-hour reserve for each watch you own and reminds you before it stops. To check a particular weekend, try the "Will my watch stop?" calculator.

Verdict

The 4R39 is a dependable 4R Seiko with two bits of dial interest: an open heart and a 24-hour hand. It's the reason the open-heart Style60's and the Zen Garden look as busy and mechanical as they do. Go in knowing what the 24-hour hand is. It's an AM/PM indicator, not a travel complication. Expect the usual 4R trade-offs: a loose official tolerance, a 41-hour reserve and no date. If that suits how you'll wear it, it's cheap to own and easy to service.

FAQ

Is the Seiko Presage Style60's SSA425 a GMT?

No. The 24-hour hand on the SSA425's 4R39 moves with the hour hand and can't be set on its own, so it only shows whether it's day or night. The Style60's SSK models with the 4R34 are the true GMTs.

How long does the Seiko Presage Zen Garden run off the wrist?

About 41 hours from a full wind, roughly a day and three quarters. If it wasn't fully wound when you took it off, it will stop sooner.

Does the Seiko Zen Garden SSA421 hack and hand-wind?

Yes. The seconds hand stops when you pull the crown out to set the time, and you can wind the 4R39 by turning the crown clockwise.

How do I set the 24-hour hand on my Seiko Style60's?

You set it with the time. Pull the crown to the first click and turn the hands. The 24-hour hand moves with the hour hand, so use it to make sure the watch is set to the right half of the day.

How accurate is the Seiko Presage SSA464?

Seiko rates the 4R39 at +45 to -35 seconds a day on the wrist. Most 4R movements run well inside that, and a watchmaker can regulate one closer.

Does the Seiko 4R39 have a date?

No. It shows hours, minutes, seconds and a 24-hour indication, and the balance is visible through the dial at 9 o'clock.

Why did my Seiko Style60's open heart stop over the weekend?

The 4R39 runs about 41 hours from full, which isn't enough for a whole weekend off the wrist. Wind it by the crown before you set it down if you want it to last longer.

Sources

• Seiko: Parts list and technical guide, Cal. 4R38A/4R39A (PDF)
• Seiko: Instruction manual for 4R35/4R36/4R37/4R38/4R39/4R71/4R72 (PDF)
• Seiko: Presage Style60's SSA425J1 product page
• Seiko: Presage SSA421J1 product page
• Grail Watch Reference: Seiko 4R39

Keeping it running

• On an average day an automatic gains roughly 4 hours of reserve per hour on the wrist, so about 10 hours of wear fills the Seiko 4R39. 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 41 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

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 4R39: 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.