Mainsprings for Sessions Black Mantel Clock

I recently overhauled this Sessions black mantel clock from around 1903 – 1910. It was a routine overhaul including polishing the pivots and installing bushings. A previous repairer had installed two screw-in bushings (a no-no!). I replaced these with KWM size 4 American bushings. The mainwheels were made with Gilbert-style clicks, which are more robust then the standard Sessions clicks.

The original mainsprings seemed too strong. The time spring was 0.0182 inch thick, and the strike spring was 0.0178 inch thick. I replaced both with thinner mainsprings, Merritt’s Antiques P-1956, 0.0165 inch thick, to reduce future wear to the mainwheel teeth. The escapement takes an excellent motion.

Repair job 4949.

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  1. This is an estimate, based on what I’ve seen in Sessions catalogs and Tran Duy Ly’s Sessions Clocks book.

    As far as I know, this type of clock always had open mainsprings.

  2. Bill, how did you determine 1903 – 1910 as the date of manufacture?
    I have a Session’s small 17 in. high oak mission clock that I am trying to determine its date of manufacture.
    Also, approx. when was the change from open springs to barrel enclosed?

    Take care,

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