Dilemma: Tissot Navigator T12 "purist" T788 circa 1969

Thread: Dilemma: Tissot Navigator T12 "purist" T788 circa 1969

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  1. #1
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    Dilemma: Tissot Navigator T12 "purist" T788 circa 1969

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Size:  913.5 KBPictured is a Tissot T12 Navigator which I just purchased. The watch has a Tissot788 movement inside which the mark has been confirmed by my watchmaker. My dilemma is that as I understand the 788 movement is a 24h or purist movement, yet this watch is timing in 12 hour increments which in turn renders the 24 hr. Bezel useless. My question is am I mistaken about the 788 being a purist or is there some trick I'm not getting?

  2. #2
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    Re: Dilemma: Tissot Navigator T12 "purist" T788 circa 1969

    Hi there,

    you got it right, the Tissot 788 should have both, a 12h and a 24h hand.

    Regards, Roland Ranfft

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    Re: Dilemma: Tissot Navigator T12 "purist" T788 circa 1969

    Quote Originally Posted by Roland Ranfft View Post
    Hi there,

    you got it right, the Tissot 788 should have both, a 12h and a 24h hand.

    Regards, Roland Ranfft
    Thank You, but I'm confused how to use this watches bezel.

    So how many times per day should the hour hand rotate?

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    Re: Dilemma: Tissot Navigator T12 "purist" T788 circa 1969

    UPDATE: I spoke to the seller who said that his watchmaker replaced a gear during service. Is it possible to change a movement with one gear? Also, where can I go to order a new part for this movement?

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    Re: Dilemma: Tissot Navigator T12 "purist" T788 circa 1969

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Size:  242.6 KBHere are the photos of the changed part.

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    Re: Dilemma: Tissot Navigator T12 "purist" T788 circa 1969

    Manufacturers often use the same base movement...then modify it for various day/date complications. Gylcine uses ETA 2893 in some versions of the Airman which have only 24hr, min, ss hands. The modification is to the 24 hour wheel tube, such that it covers the hour wheel tube...thus no place to mount a conventional hour hand (there may be ss post, cannon pinion height differences as well).

    Your Tissot had the minute wheel replaced. Conversion from 12hr to 24hr display is often accomplished by changing the ratios of the minute wheel and hour wheel. Looking at Jules Borel parts list, the 788 minute wheel is used in many calibers...including 12hr displays...so this change is not likely the issue (and expensive minute wheel, BTW!!!). The cannon pinion and hour wheels for the 788 are used on one other caliber: TIS 2531...both 24 hour display...either/both could be an issue. A competent watchmaker should be able to sort this out for you.
    Regards, BG

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