Plymouth (by Seth Thomas) 1940 Mantel Clock

I repaired this modern-styled mantel clock. Seth Thomas made it and sold it under the “Plymouth” name. The movement has two numbers stamped on the back:

  • 11 40 (November 1940) on left rear movement leg;
  • 4506 (the model number) on strike hammer bridge.

The case is 8 5/8 inches tall and 12 3/4 inches wide. The dial is silver plated brass, with printed numerals, etc. The minute hand is 2 1/2 inches long from center to tip. The hands and hand nut are silver-plated. The minute track is 5 inches outside diameter. The movement runs over 8 days on a winding and strikes the hours and half hour on 2 chime rods.

See more photos.

This clock has Seth Thomas’s later type of mantel clock movement (the one that replaced the No. 89). In the past, I didn’t like this movement, because it is subject to severe wear due to its overly strong mainsprings. I have discovered that it will run well with weaker mainsprings (see 1940s Seth Thomas 8 Day Time and Strike Clock Movement for another example of this movement, and Two Seth Thomas “Plymouth” Tambour Mantel Clocks, 1938 and 1940 for another example).

This movement has suffered wear (see photo of the worn bushing above). A previous repairer installed many bushings off-center. It appears that first, off-center rear mainwheel bushings were installed, then all the other bushings were installed off-center to keep gear depthing correct. I tested all the gear depths, and left the bushings off-center except for one that needed moving. The rear time second wheel pivot was rough (the surface was like a fine file), which is why there was so much wear to its bushing. I polished all the pivots and replaced a bent wire in the center pinion.

I replaced the too-strong original mainsprings with weaker ones.

Original mainsprings:

  • Time 11/16 x 0.0183 x 80 inches;
  • Strike 11/16 x 0.018 x 80 inches.

New, thinner mainsprings:

  • Time 11/16 x 0.0161 x 80 inches (Timesavers 20506 shortened by 16 inches);
  • Strike 11/16 x 0.0167 x 80 inches (Empire Clock 280-17-505 shortened by 16 inches).

(Note: supplier Empire Clock is no longer in business.)

The movement runs extremely well these mainsprings, and would probably run well with even thinner springs (perhaps 0.015 inch thick for the time mainspring). Both mainwheels are 25% worn due to the original strong mainsprings. The clock runs well in spite of the tooth wear.

The pendulum bob is 1 13/16 inches diameter and weighs 4 ounces. The suspension spring is 0.004 inches thick, and the pendulum rod is 2 millimeters diameter.

The inside of the rear door has an instruction label. The label includes the following:

Guarantee and Directions
Covering Clocks equipped with
No. 4300, 4500 and 4600 Series 8-Day Pendulum
Strike Movements in Tambour Cases.

Text here about the clock

Instruction text here

The Plymouth Clock
Thomaston, Conn.

The number 414 is stamped at the bottom.

Repair job 5534

Key: No. 6 large end, No. 0000 (4/0) small end.

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  1. I acquired a Plymouth mantel 8 day strike.Mine has the number 4503 on right and on left is marked 10 41.It has embossed numbers but does not read Plymouth in the center or bottom of face.Bottom reads made in USA.Instructions read Z-34P on bottom left.Also design is a little different with two pyramid like shape on each side with 5 straight lines in the middle between them.Very accurate and loud.Please tell me what do I have and what is the value with a few minor scratches.Thanks MIKE

  2. Hi I have a Seth Thomas Plymouth 1940 Mantel Clock with mostly all the same markings. 11 – 40, mine is a 4606 and has Z-34P. Been a while since it has been running. When I get it going the clock runs about 3 minutes and a funny thing happens when it slows down, as the pendulum stops dead at the position of about 28 minutes to the hour instead of on the 30 mark. seems to run good until it suddenly stops at that point. It would probably would continue to run but gets hung up. Never seen a clock do this before. I have many mechanical clocks and this is the first time I ever seen this happen. Thanks, JDuell

  3. Hi.
    Have a Seth Thomas Ships Wheel Tambour Mantel Clock with the same label you describe here. Where yours is marked 11 40, mine is marked 1 40. It is also marked with the number 4506 and a plain Z-34 with no letter after.
    There is another set of numbers inscribed smaller and more lightly on it. They are 110/1197. Do you have any idea what they mean? Is it, perhaps, the 110th clock out of 1197? Or is it something else entirely?

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