Seth Thomas Adamantine Clock Movement with Thin Time Mainspring

I recently repaired a Seth Thomas Adamantine mantel clock made around 1905. It has a No. 89 movement. This movement is very efficient in operation, due to the use of a deadbeat escapement. Even with a thin time mainspring, these movements typically take an excellent escapement motion.

This particular example has thin, original mainsprings.

Time Mainspring: 3/4 x 0.0167 inch.

Strike mainspring: 3/4 x 0.0163 inch. (Unfortunately, I had to replace the strike mainspring because it had a rough action when nearly wound, typical of springs that may break soon. I used a new Merritt’s Antiques P-1956).

Many examples of the No. 89 movement have thicker springs, quite often around 0.0175 inch thick, sometimes thicker. After proper repair, this movement will run well with thin springs.

Here is a video of the escapement motion, first run down 6 1/2 days, then fully wound:

Repair Job. 4970.


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4 comments

  1. You need to remove the minute hand (by taking out the tapered pin), rotate the minute hand 90 degrees clockwise, then put it back on.

  2. I have an 1892 adamentine that bongs once at 15min past the hour and 15min before the hour the right number of bongs, any idea how to make it strike on the half hour and at the hour. I am just getting into clocks, thanks Ron

  3. Several different types of pendulums were used:

    1) Lead with regulating nut in the center

    2) Gold color with picture of boy sitting on fence, no regulating nut

    3) Lead with brass cover on one side, no regulating nut.

    The rough feel mainly applies to mainspring that have been cleaned, since dirty ones can feel rough but not be about to break. It is kind of a squeaky sound when unwinding the spring after it is fully wound, but can only be heard when the spring is let down in the mainspring winder (not in the clock at normal operating speed).

  4. Do you happen to have a photo of the proper pendulum for a clock of this type? I am trying to ascertain whether mine is original or a replacement. Also you mentioned that a spring that may break soon has a rough movement, can you explain that statement in greater detail, since I would like to understand what you mean so that I can check my clocks for such problems before they break. Thank you,
    -Jason

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