How to adjust a 400 day clock

Written by max stout
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How to adjust a 400 day clock
400 day clock with torsion pendulum. (anniversary clock image by Pix by Marti from

The 400 day clock is operated by a torsion pendulum system. Unlike clocks that have a pendulum that swings from side to side, the torsion pendulum oscillates in a circular motion and is suspended by a long, thin and flat steel spring. Adjusting both the beat and the timekeeping of the 400 day clock are sensitive procedures usually performed by experienced clock repair professionals. However, the clock owner with a moderate understanding of mechanics and an ability to work with a delicate touch is capable of making the adjustments. The project is initially completed in one hour or less with a few tools.

Skill level:

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Things you need

  • Small circular level
  • Small flat-tip screwdriver
  • Smooth jaw needle-nose pliers

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  1. 1

    Remove the protective glass dome from the 400 day clock by lifting it straight up until the bottom of the dome clears the uppermost part of the clock. Use care when removing the dome as the glass is thin and may crack or break if impacted.

  2. 2

    Level the clock by turning the adjustable feet on the bottom of the base as necessary to ensure that the bottom centre point of the pendulum is in the centre of the brass cup located on the base. Make certain that the pendulum can move freely without contacting the sides of the cup. If the 400 day clock does not have a cup in the base, use a small circular level to perform this step.

  3. 3

    Locate the anchor pin at the top of the clock movement. The anchor pin is the small diameter post that protrudes through a small brass fork attached to the thin suspension spring and is fixed to the anchor. Notice the escape wheel of the movement and the two pallets that are attached to the anchor.

  4. 4

    Slowly turn the pendulum until one of the pallets releases the escape wheel, allowing it to advance one tooth of the wheel. Stop moving the pendulum immediately when the tooth of the escape wheel is released.

  5. 5

    Gently release the pendulum and allow it to oscillate in the opposite direction. Observe the escape wheel and the pallet that once again releases it. If the escape wheel advances at the same time the pendulum stops, the 400 day clock beat adjustment is fine.

  6. 6

    Use a flat tip screwdriver or smooth jaw needle-nose pliers to turn the saddle that the suspension spring is connected to if the pallet does not unlock the escape wheel tooth and a beat adjustment is needed. The saddle is located at the top of the clock movement mounted on the suspension spring bridge.

  7. 7

    Turn the screw with the screwdriver, if applicable, or turn the saddle using the smooth jaw needle-nose pliers slightly in the direction where more rotation is needed. Slightly means a barely detectable movement of the tool is used for this adjustment. Take care not to twist or otherwise deform the delicate suspension spring while making the adjustment.

  8. 8

    Continue making the beat adjustments until the escape wheel teeth release at the end of each rotation.

  9. 9

    Stop the pendulum at the point where it reverses its oscillating cycle to adjust the timekeeping of the 400 day clock. Keep the pendulum in the spot where you stopped it as you make the needed time adjustment.

  10. 10

    Turn the regulating disc on the top of the pendulum according to its marking to make necessary changes in its timekeeping. Turning the disc in the direction of the “F” will speed up the clock and turning in the direction of the “S” will slow the clock.

  11. 11

    Release the pendulum slightly past the point where it was stopped.

  12. 12

    Turn the minute hand clockwise until the correct time is set. Avoid moving the hour hand as the minute hand is rotated.

  13. 13

    Replace the glass dome over the 400 day clock. Take care handling the glass dome.

Tips and warnings

  • 400 day clocks operate at a slow pace. Allow the clock to run for several days between adjustments.
  • Initially, make timekeeping adjustments on the pendulum disc of no more than a 1/8 inch turn in the necessary direction.
  • Record the amount of adjustment made each time. This will help when making future adjustments.
  • Care must be taken when making any adjustments to the 400 day clock. Suspension springs are delicate and can be damaged if twisted or distorted in any way.

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