Modding The New Seiko 5 Sports 38mm SRPK29, SRPK31, SRPK33 and SRPK35

modding the 38mm srpk seiko 5

Introduction:

We got our hands on a few of the new 38mm Seiko 5 Sports watches this week to test what parts you can modify and its relation to the SKX013. This article will be covering all of the mods (or lack their of) that you can do to the SRPK’s. If you are looking for a great watch overview article check out Hodinkee’s “Giving the people what they want.

To sum up our findings, we want to preface that when Seiko announced the release of this new 38mm series we whole heartedly though that this was going to mirror what the Seiko 5 SRPD’s did for the SKX007. We are hear to announce that (unfortunately) Seiko did not follow that relation with its new 38mm for the SKX013. In fact, only bracelets/straps, bezel inserts and standard movement upgrades for its 4R36 are cross compatible. Let’s get into it!

Modding Breakdown

Case & Caseback:

The case size and dimensions are similar to that of the SKX013, but the only cross over parts that it can house is the movement assembly (dial, hand, movement), and SKX013 click springs. Now, you could take the movement assembly and put it into a SKX013 case and build it from there. You can use SKX013 case backs on the new case, but need to reuse the caseback gasket as the diver gaskets are too thick.

Bezel & Click Spring:

SKX013 Bezels do not fit. Click springs do.

Bezel Insert:

The most exciting mod you can do is with SKX013 bezel inserts! SKX013 bezel inserts fit.

Crown:

SKX013 crowns do not fit. Like with the SRPD’s it has a push-pull crown.

Crystal & Crystal Gasket:

The saddest part of this is that SKX013 crystals do not fit, and the gaskets as well. The Outside diameter of the SRPK’s is 27.5mm

Chapter Ring:

SKX013 chapter rings do not fit. The SRPK’s have a new design and is top loaded.

Dial:

28.5mm dial, but the indicies are applied further in like the SKX013 so technically you can use SKX013 designed dials and they will fit inside the chapter ring inside diameter.

Hands:

The longest pin to chapter ring length you can fit is 12mm. So when modding the hands take that into account especially for the seconds hand.

Movement:

4R36 standard upgrades like day/date wheels, rotors, etc.

Bracelet & Straps:

Straight end 20mm straps fit. SKX013 bracelets are interesting: The original spring bars are too thin to hold the SKX013 bracelet in place. The fat spring bars that come with SKX013 bracelets are perfect, but the SRPK case drilled holes are not large enough for the fat spring bar tips to fit in. You can make an adjustment to the tips to retrofit them into the small holes as a work around.

Specs

Brand: Seiko
Model: Seiko 5 Sports
Reference Number: SRPK29 (black), SRPK31 (champagne), SRPK33 (teal), SRPK35 (orange). 

Diameter: 38mm
Thickness: 12.1mm
Lug-to-lug: 44.2mm
Lug width: 20mm
Case Material: Steel
Dial Color: Various (see ‘Reference Number’)
Indexes: Applied
Lume: Yes, hands and  markers (Seiko Lumibrite)
Water Resistance: 100 meters
Strap/Bracelet: Steel bracelet with fold-over clasp and pushbutton release

Movement

Caliber: Seiko 4R36
Functions: Hours, minutes, seconds, day, date
Power Reserve: 41 hours
Winding: Automatic (can be manually wound)
Frequency: 21,600 vph
Jewels: 24