The Seiko GMT and What That Means For Watch Modding
A new GMT movement is in town and nobody was ready! Seiko has done it again by introducing a new automatic GMT watch. Just when you think they’ve done it all, they surprise us again. The new Seiko GMT models currently come in 3 different classic colors, The SSK001 is black, the SSK003 is Blue, and the SSK005 is an orange dial. Three beautiful classic colors that will be sure to draw attention. But what movement did Seiko use for this new GMT? Well they created a new movement based off of the 4R family of movements, the 4R34 GMT. With the new 4R34 comes the unbranded NH34 Movement for modders and microbrands! This will open a whole new world for modding Seiko’s and help curb the GMT insert police. Let’s get right into it…
NH34 Movement Specs
- Caliber number: Seiko NH34 (4R34)
- Power reserve: 41+ Hours.
- Movement type: automatic GMT
- Frequency/Vibrations per hour: 21600 bph.
- Accuracy: -20~+40 sec per day.
- Hacking and Handwind: Yes
- 24 Jewels
The NH34 Specs are almost identical to the NH35 movement except for a few minor details. The first being that the movement is 0.1mm thicker, but don’t worry! This will not affect your modding potential. And the second being the most important, it has a GMT hand!
Now, I know what you are thinking, What parts will actually fit? I mean we are watch modders after all, we just can’t seem to keep any Seiko stock. So let’s go over what we know will fit and what won’t.
What mod parts will fit the seiko GMT (SSK001)
So now the question we are all asking, what parts will fit the new Seiko GMT SSK models? let’s take a deeper dive into what makes this Seiko GMT different from other 5KX models.
Case and Bezel
The Seiko GMT will not be as easy to mod as some of the previous Seiko 5 models. Nothing is quite plug and play as of yet, excluding a few parts.
So, lets start with the Case and Bezel for the new Seiko GMT. Right away you will notice a difference in bezel action. The Seiko GMT has a smooth rotating bezel with no clicks. Once removed you will see that the bezel is even more different than just the click action. For one, the inner diameter is bigger. But that’s not the issue, the issue is that the bezel groove for the inserts sits a little deeper. This makes it hard to line up aftermarket bezel inserts to the glass without padding.
Now, one good thing about the case is that the crown is identical to the SRPD push crown, unfortunately, it will not fit Seiko SKX screw down crowns. The Stem for the NH35 is identical to the NH34 and is also the same length for the SSK case.
Chapter Ring and Glass
Let’s move on to the Chapter Ring and the Hardlex Glass. This will be another huge difference between the SSK and the SKX. For starters the chapter ring on the SSK is extraordinarily thicker. Not only is it thicker, but it also comes with 2 alignment tabs more reminiscent of the SRP Turtle. Also, a difference in the case design has the crystal gasket sitting right on top of the chapter ring instead of having a side step like the SKX cases.
Now to get to the Hardlex Vs. Sapphire dilemma. The OEM Hardlex from the SSK is 2.95mm thick which makes it slightly thicker than the Seiko SKX. However, the diameter of the Hardlex is still 31.5mm like the aftermarket sapphires. To top it off, the crystal gasket is not the same as the SKX007 crystal gaskets and are more similar to the SRPD gaskets.
SSK GMT Dial
The dials! We all want to know about the dials. Well first off, the date window of the 4R34 does line up with the standard NH35 date window dials. The size of the dial is also 28.5mm just like the aftermarket Seiko dials.
Unfortunately, there is one major difference… the center hole. Because of the Seiko GMT hand on the bottom of the stack being 2.2mm in size, the opening for the center of the dial needed to be bigger. The center hole of the dial sits at a hair smaller than 2.9mm in diameter. Most seiko dials come with a 2mm center hole meaning they will not be plug and play with the NH34.
In order to fit an NH35 or 4R35 dial onto the movement you will need to file out the center hole. It won’t be pretty and is not recommended unless you know what you are doing.
NH34 Hands
No surprise here, but the NH34 (4R34) hands are identical in hole size and length to all other NH35 hands. The only difference being the added 4th hand for the GMT function which sits at 2.2mm hand pinion size. Don’t worry though as Watch-Modz currently sells GMT NH34 hands!
How Can I Mod The Seiko GMT SSK?
So now you’re probably thinking that none of this sounds good, right? Well we have a very simple solution to get you modding a Seiko GMT in no time flat!
The easiest solution to all of these problems would be to transfer your SSK dial movement and hands right into an Aftermarket case! Once you transfer it to a new case, you’ll be able to use any aftermarket chapter ring, bezel, double domed glass (flat sapphires will not fit the higher hand stack of 0.4mm), and you’ll also gain the benefit of a screw-down crown! Now you can enjoy modding the GMT 4R34 (NH34) until all the aftermarket parts suppiers start releasing all of the parts for this model in a few months time. Be on the look out for new parts dropping!
The Watch Modding community feels revitalized after the release of this new model, and I see some amazing builds in the near future! If you would like to join the disscussion with the modding community, then join us at the Watch Mod Enthusiasts Group.