Plymouth (by Seth Thomas) Round Top Mantel Clock, 1940

This “Plymouth” round top mantel clock (made by Seth Thomas) is 9 3/4″ tall and 8 3/4″ wide. The minute hand is 2 1/2″ from center to tip. It has a mahogany case with a lighter color veneer panel at the bottom, and a printed metal dial.

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Repair job 8727. As mentioned before, this type of movement has very strong mainsprings that cause severe wear. The movement is model 4501, and the original rear movement plate has a date of 3 40 (March 1940). The wear was so severe, and a previous repairer had installed some bushings off-center, that I bought a parts movement from eBay and ended up using the front and back plates, time and strike mainwheels, and time second wheel. A previous repairer had filed the gear pivots tapered (on gears T4, T5, T6, and S3 through S6) so I filed them parallel and burnished them.

The escapement is deadbeat with diamond-shaped steel pallets set into a nickel-plated brass body (like the No. 124 chime movements of this period).

I installed 19 bushings, and replaced the mainsprings with much thinner ones. I inserted new mounting grommets with brass sleeves in the four holes that mount the movement to the case.

The original mainsprings:

Time: 11/16 x 0.0182 to 0.0185″
Strike: 11/16 x 0.0183″

The new mainsprings are Merritt’s MS298 11/16 x 0.0155 x 108″, shortened by 22″. They are supposed to be 0.015″ thick, and previous examples I had measured 0.015, but these measure 0.0155. No big deal. Even thinner mainsprings would work, as the strike runs plenty fast, and the pendulum makes a very good motion! I hope these thinner springs will significantly reduce future wear, compared to the original thick ones. One thing about these German made mainsprings, is that the way they are tempered (or whatever they’ve done), they are very strong compared to other mainsprings for a given thickness, and the repairer must be careful not to install mainsprings that are too strong.


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