Seiko Caliber 4R35

Manufacturer	Seiko
Caliber Number	4R35, 4R35A, 4R35B
Movement Type	Automatic
Diameter	27.4mm (casing 27mm)
Thickness	5.32mm
Jewels	24 23 (see below)
Vibrations Per Hour	21,600 bph
Lift Angle	52 or 53 degrees (see below)
Power Reserve	~40 hours
Hand Windable?	Yes
Hand Winding Direction	Clockwise
Rotor Direction	Bi-directional (Magic Lever)
Hacking?	Yes
Anti-Shock System	Seiko Diashock
Regulator System	ETACHRON
Functions	Hours, minutes, central seconds, date calendar at 3:00
Country of Manufacture	Japan
Known Models	(Add yours in the comments below…)

The Seiko caliber 4R35 is an automatic used by Seiko Watch Corp. in their own branded watches. This movement was released circa 2011. This caliber was considered to be an upgrade from the popular 7S26 movement as it offers the user the desirable hacking and hand-winding functionality.

In Seiko’s own words:

“SEIKO Automatic mechanical Cal. 4R35A is developed based on Cal. 7S series and Cal. 6R series design with two specifications as follows: 1. Manual winding function. 2. Second hand stop function for time setting (2nd click position of the crown).”

Caliber 4R35 VS SII NH35:

The caliber 4R35 is basically a Seiko-only version of the NH35A. Seiko Instruments (aka SII) sells the NH35 to other manufacturers for use in non-Seiko watches. At the time of this post, the 4R35B has 23 jewels and the NH35A has 24 jewels (see below).

Caliber 4R35 VS 4R36:

There is also a similar caliber 4R36. The difference between the two is that the 4R35 has a date calendar complication at 3:00, and the caliber 4R36 has a day/date at 3:00. Everything else is the same, including dimensions, jewels, accuracy, etc. Despite tech sheet misinformation, the caliber 4R35B has 23 jewels and the 4R36A has 24 jewels (see below).

Differences Between 4R35A and 4R35B?

The “A” in 4R35A indicates that it is the first generation of this caliber. The official tech sheets show that the 4R35B was an upgrade from the original caliber where Seiko increased the jewel count from 23 to 24 jewels see update below. This happens to be the same jewel count at the 4R36 mentioned above, so it could be for ease of production and documentation. Other differences as listed in the technical docs:

• Lift Angle: 4R35A = 52 degrees / 4R35B = 53 degrees
• Power Reserve: 4R35A = 41 hours / 4R35B = 40 hours

Update: It appears that the parts lists for the 4R35A and 4R35B show a difference of at least 23 individual parts. Seiko has even updated their tech sheets with more information regarding the difference between A vs B.

In Seiko’s own words:

“SEIKO Automatic Mechanical Cal.4R35B is replacement caliber of Cal.4R35A. Construction of B series are same as A series, but using new parts. Since the size of the movement is same as A series, the complete movement can be assembled into the watches which originally have the A series movement; however, as the parts are not convertible, please use the appropriate parts for each caliber. The difference between Cal.4R35 and Cal.4R36 is a calendar mechanism” –source

UPDATE: 23 or 24 Jewels Confusion

There is much confusion in the watch community around the caliber 4R35B jewel count. Blogs and watch sellers often refer to the 4R35B as having 24 jewels, this is because that is what Seiko’s official documentation has stated since the tech sheets were published in 2011. Interestingly, the conflicting information in the tech sheet appears to be caused by Seiko combining the calibers 4R35B and 4R36A in one document. The original 4R35A had its own tech sheet. The rotor drawing on the 4R35A shows the caliber number and jewel count spelled out (as it would look on an actual watch), however, the 4R35B/4R36A drawing has a blank rotor without any markings, continuing the cause for confusion.

We have not seen a caliber 4R35B powered watch with rotor markings indicating 24 jewels. The Caliber Corner Community is also backing up the discrepancy in the comments below, so we reached out directly to Seiko for information:

“Dear Seiko, can you please confirm if the 4R35B has 23 or 24 jewels? Tech sheets say the “B” has 24 jewels, but many watches with a 4R35B signed rotor say 23 jewels. Thank you in advance for any clarification you can provide. -Caliber Corner”

Dear Customer,
We have inspected few watches with B movements, and they all state 23 jewels.
Thank you for your feedback, we are in process of correcting that information.
Kind Regards,
SWA

This confusion is further perpetuated due to the fact that the 4R35B is regarded as the “Seiko only” version of the SII NH35A which has 24 jewels.

Please comment below if your 4R35B powered watch has 23 or 24 jewels.

Accuracy Rating:

Seiko claims that the accuracy of caliber 4R35 is between +45 / -35 seconds per day. This rating is based on normal daily wear on the wrist in temperatures between 5 ºC and 35 ºC. When testing your watch for timekeeping, make sure it is fully wound.

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

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:

Examples of Watches With This Movement: