Modding a GMT watch to 24-hour?
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  1. #1
    Member ned-ludd's Avatar
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    Modding a GMT watch to 24-hour?

    WARNING: If you abhor modification of watches, please do not read this or criticise the idea simply because you don't approve.


    The market for pure 24-hour watches is limited so there's not a lot of choice out there. Pure 24-hour mechanical movements seem to be the sole domain of the high end manufacturers like Breitling, Sinn and Glycine, or more mass market manufacturers like Raketa and Vostok.

    I've noticed that makers of low and mid-range 24-hour watches - like No-Watch, Mr Jones and UNO - simply use 'GMT' movements and omit the 12-hour hand. Movements like the mechanical Seagull 2557 and quartz Ronda 515.24H are cheap, readily available and are to be found in the majority of watches presented as 24-hour models.

    This led me to thinking that if one craves more variety in watches of the 24-hour type one could use suitable existing GMT models and simply remove the 12-hour hand from them. GMT watches that lend themselves to this would need to have 24-hour marks on the dial and no 12-hour marks. I've found numerous current, inexpensive watches that I believe would lend themselves to this modification. For example:

    * Seiko Criteria SLT083, SLT10x
    * Seiko Prospex SUN0xx
    * Timex T2P42x
    * Citizen Promaster GMT BJ7081-51E
    * Parnis Military GMT (Seagull 2557)
    * Invicta 6988

    Removing the 12-hour hand from a watch is easy but merely eliminates it as a visual distraction. A watch without an obvious hour hand and a differently shaped or coloured GMT hand may just look broken. Replacing the GMT and minute hands with a matching pair would be the obvious thing to do and is within the capabilities of many amateur watch repairers. The result would be an aesthetically and functionally passable 'pure' 24-hour watch.

    The trick to replacing the hands, of course, is finding ones of the right size or modifying existing hands to fit. That may prove to be the biggest obstacle to doing so, especially given how difficult it seems to even get hand measurements for the various GMT movements found in the candidate watches.

    It could be argued that this modification may confuse the casual observer but given that most casual observers are already confused by 24-hour watches that's not a problem. For many 24-hour enthusiasts that's probably part of their appeal!

    I have already acquired a couple of GMTs for experimentation. It will be a challenge but it keeps me entertained and off the streets.
    Last edited by ned-ludd; July 23rd, 2017 at 12:12.
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  2. #2
    Member mougino's Avatar
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    Re: Modding a GMT watch to 24-hour?

    Interesting project!

    Good luck and keep us posted about your progress!

    Nicolas


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  3. #3
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    Re: Modding a GMT watch to 24-hour?

    Some of the Glycine Airman watches come as GMT or purist versions and do exactly what you mention about. At least that is my current understanding.


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  4. #4
    Member wemedge's Avatar
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    Re: Modding a GMT watch to 24-hour?

    I've had this modification done twice before- one was a Steinhart GMT, with the 12-hr hand simply removed, and the other was a Glycine Airman GMT which was converted to purist by Werner Siegrist.

    I ended up having the Steinhart returned to its original state eventually, but kept the Glycine as purist.
    Last edited by wemedge; July 25th, 2017 at 16:04.
    It's 1700hrs somewhere...

  5. #5
    Member ned-ludd's Avatar
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    Re: Modding a GMT watch to 24-hour?

    Quote Originally Posted by wemedge View Post
    I eneded up having the Steinhart returned to its original state
    That's part of the beauty of it: any watch with removed or replaced hands can be restored easily to its original state.
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  6. #6
    Member ned-ludd's Avatar
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    Re: Modding a GMT watch to 24-hour?

    I now have several candidates for my conversion project. Each of these I've had to buy new because I can't find any second-hand ones. I bought four GMT quartz watches: a Seiko Criteria SLT083, Citizen BJ7070-57E, Seiko SUN069 and a Timex T2P424.

    This is a good selection for a collector because they're all functionally different: one has a compass bearing bezel (handy for New Earth Time), one has an E6B flight calculator, one has a world time bezel and one has a 24-hour bezel. Also, one is a perpetual calendar, one's solar powered and one's kinetic powered. As to the uniformly black faces, stainless steel cases and bracelets, well I just prefer that in a watch.

    The Timex T2P424 is a handsome watch; it offers three time zones (love that 24-hour bezel!) and a really cool Indiglo face. Sadly, however, it's not a candidate for conversion due to its mode of operation.
    • Every press of the button at 2 (04) o'clock moves the GMT (24-hour) hand forward by thirty minutes. If converted, in normal use it would be too easy to accidentally bump that button and thus lose track of what hour it was.
    • When you pull the crown out to adjust the time, the GMT hand moves to the 12 (24) o'clock position. This means setting a converted watch correctly would require rotating the minute hand until the date ticked over (i.e. 24:00) and then counting full revolutions until the desired hour is reached (there being no 12-hour hand to guide you), then pushing the crown in and moving the GMT (24-hour) hand into place using the button at 2 (04) o'clock.
    I'd love to keep the Timex but if it can't become a 24-hour watch it has no place in my collection; I have to sell it.

    So three watches are for the 'chop' but as they're brand new I'm frightened of wasting good money by breaking them so I've chickened out on doing the conversions myself. As soon as time and budget permits I'm going to take them to my preferred watchmaker to get him to do the job.
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    Re: Modding a GMT watch to 24-hour?

    I've been thinking of doing exactly this as well.. the 2431 based Vostok's automatics look like they could be a good candidate, but some would need a new dial which makes it practically impossible... unless anyone knows where to make custom dials?
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  8. #8
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    Re: Modding a GMT watch to 24-hour?

    I'm interested in converting a 24 hour watch with a rotatable "diver/timer" bezel to a two time zone 24 hour watch by replacing the "diver/timer" bezel with a 24 hour bezel. The watch - a Russian Vostok Komandirskie K-35, which I have...

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    The bezel... I've seen a few rotatable 24 hour bezels that supposedly will fit the watch (and I even have one), but so far haven't found the one I want to use... I have a rotatable thin stainless steel 24 hour bezel that should fit...
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    However, ideally, I'd like to find one shaped & sized more like the watch's stock rotatable bezel, but with 24 hour markings. If that's not possible, I'd like a rotatable bezel with a ceramic insert but with white 24 hour markings (so, far the only one I've seen that I know is properly sized to fit is black with yellow markings and I don't think yellow markings would go well with the watch's dial face). Ideally, I'd like the ceramic bezel insert's background to be black/blue - black for the "dark" hours of 6-18 and blue for the "daylight" hours of 18-6... I'm still looking for such a rotatable 24 hour bezel/ceramic bezel insert combination that will fit the watch, but eventually I may settle for the thin stainless steel 24 hour bezel I already have...
    Last edited by r-gordon-7; August 13th, 2017 at 22:58.
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  9. #9
    Member ned-ludd's Avatar
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    Re: Modding a GMT watch to 24-hour?

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    That looks like a Vostok 100 case (just like mine). I've always thought that bezel's edges sharp enough to draw blood if given half the chance. To soften it, perhaps a Murphy Manufacturing VO1060 bezel would suit? Then a Seiko SKX007 24 insert (from yobokies or elsewhere) would finish the job. Getting a colour and font to suit the face (mine's black, BTW) could be difficult. Personally I'd just go for a black/white 0600-1800 split to keep things simple.

    It's certainly something that's been done by others and if I didn't have so many other projects on I'd try it myself. Maybe later.

  10. #10
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    Re: Modding a GMT watch to 24-hour?

    Thanks, ned-ludd for the lead to Murphy Manufacturing. I've now contacted & been in touch with Dave Murphy, trying to figure out whether their VO1060 (or perhaps their VO150, though that one's currently out of stock) bezel would actually fit the Vostok Komandirskie K-35 - preferably with a DLWwatches "Ceramic Bezel Inserts - GMT Batman Bezel Insert" for Seiko SKX007 (https://www.dlwwatches.com/collectio...s-gmt-batman-1). I've also been in touch with Damien at DLW. Both have been very helpful & prompt to respond, but apparently none of this is quite as simple a determination or as definitive as it might seem. So, though I'm usually not a gambler, I may have no choice but to take a shot by ordering the parts that are "most likely to work" - and then see if in fact they do... (Or maybe just install the Meranom stainless steel 24 hour bezel I already have that I believe is supposed to fit...?)
    l3wy likes this.

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