Repairing the M4 Motor in Seth Thomas Electric Chime Clocks

October 25, 2014 | By | Reply More

I recently repaired a Seth Thomas Legacy 2 E electric clock with Westminster chime. This is an older example of the “Legacy” (made in 1953) in a beautiful walnut case with nice figure to it. The dial is made of engraved and silvered brass. The case is 14 3/8 inches tall with handle and 12 1/2 inches tall without handle. It is 10 3/4 inches wide, and the dial’s minute track is 5 3/4 inches outside diameter. The minute hand is 2 7/8 inches long.

The label inside the back door has the date code 5310 (October 1953). The movement’s date code is 52-12 (December 1952).

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Seth Thomas Legacy 2 E Electric Chiming Mantel Clock

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Pinion side of the M4 motor

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Rotor side of the M4 motor

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Movement B1752 of the Legacy 2 E

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Rear view of movement and chime rods of Legacy 2 E

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Repair job 6385. Movement No. B1752, date code 5212 (December 1952). I disassembled and cleaned the movement. The fan flies (governors for chime and strike) were loose on their arbors, I tightened them to a light tension. Time gear T4 had flat tooth tips, and the pivot had been turned down to 1 millimeter diameter. I replaced this gear with a good used one. I installed 25 bushings.

The motor had wear in the bearings. A replacement motor is available, and I installed one in the clock. It ran but made too much noise because its pinion isn’t shaped correctly. (The motor is quiet running by itself, but noisy in the clock).

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The replacement for the M4 motor that is available today. The shape of the pinion teeth make it run noisily in some clocks.

I took the original motor apart and cleaned it. Then I bushed both bearings. I lubricated, reassembled the motor, and put it in the clock, and it ran very quietly!

Motor bearings, rotor, arbor and pinion

Disassembled M4 motor. From left to right: the rotor, the bearings and the steel washer that goes between the rotor and the front bearing, and the rotor with its pinion.

Cleaning and Bushing the M4 motor:

  1. Drive shaft from rotor (don’t remove gear, it is on too hard). Don’t lose the small steel washer between the rotor and the bearing.
  2. Mark the bearings so they can be put back on the correct side of the motor
  3. With large punch, drive out the bearings. Push on the rotor side of the motor to drive them out.
  4. Clean the rotor, washer and the bearings.
  5. File holes in bushings to center them
  6. Mount each bearing in the lathe, hand hold the #3 KWM reamer, and turn the lathe by hand to ream the bearing for the bushing. Insert each bushing from the outside end of the bearing.
  7. Lightly fit the bearings in the motor and insert the arbor to test alignment and hole size – broach if necessary. (For a recent job I used KWM American system bushings #33535 (bore 1.5 mm diameter 2.7 mm, height 3.5 mm) and they fitted without needing broaching.
  8. Final clean the parts.
  9. Insert the bearings into the motor. Periodically check their alignment as they are being driven it.
  10. Use a syringe to insert Molykote 44 Light by Dow Corning or other grease into the motor.
  11. Add grease to the recess inside the hub of the rotor. If there is a recess in the front bearing, fill it with grease.
  12. Add a bit of oil to each bearing – I use Castrol Syntec 5W-30. (This may not be necessary).
  13. Insert the arbor.
  14. Install the washer.
  15. Drive the rotor onto the arbor.

If the bearings are good, do the following:

  1. Drive the arbor out of the rotor (don’t drive it out of the pinion – it is on too tight);
  2. Don’t lose the small washer between the rotor and the front bearing;
  3. Clean the rotor, arbor with pinion and washer in the cleaning machine;
  4. Wipe the oil and grease from the motor bearings, clean with contact cleaner and pegwood.
  5. Use a syringe to insert Molykote 44 Light by Dow Corning or other grease into the motor.
  6. Add grease to the recess inside the hub of the rotor. If there is a recess in the front bearing, fill it with grease.
  7. Add a bit of oil to each bearing – I use Castrol Syntec 5W-30. (this may not be necessary)
  8. Insert the arbor.
  9. Install the washer.
  10. Drive the rotor onto the arbor.

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Category: Clock Repair

Last updated: May 7, 2017

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