Clock movements explained
The movement is the engine of a clock. Here is how the two main kinds work, how to identify the one in your clock, and what to measure before you replace it.
What a clock movement is
The movement is everything inside a clock that makes it keep time and turn the hands: the power source, the part that regulates the speed, the gears, and the shaft the hands sit on. The case, dial and hands are fitted around it.
Clock sellers often call it the motor or the mechanism. If a clock has stopped and a fresh battery or a proper winding does not help, the movement is usually the part that needs attention or replacing.
See also: every part of a clock, labeled on OnlineClock.app.
Quartz movements
Most wall and desk clocks sold today use a quartz movement: a small sealed plastic box run by a battery. A quartz crystal inside vibrates at a steady rate, and a tiny motor turns the hands in steps. They are cheap, accurate enough for daily use, and very common.
One supplier of clock parts states plainly that the gears in battery movements cannot be repaired or replaced, so if a quartz movement still fails after a fresh battery, the whole unit is swapped. The same supplier says weak or mixed batteries cause most quartz problems, and that the battery must touch the metal contacts properly. Quartz movements also come with extras, such as a pendulum drive, a sweep (non-ticking) second hand, chimes, or radio control.
Mechanical movements
Mechanical movements are powered by a wound spring or by hanging weights, and their speed is controlled by a pendulum or a balance wheel through the escapement. They are found in grandfather, mantel, regulator and cuckoo clocks.
Movements from the main German makers such as Hermle and Kieninger have numbers stamped on the back plate. A seller of replacement movements explains that a Hermle number has three or four digits, a dash and more digits, with a pendulum length in centimeters below it on pendulum clocks, and that two digits above the number often show the year it was made. Kieninger numbers are only partial and are matched using a chart. The same seller notes that with a letter in front, such as A, a movement may follow the Seth Thomas naming system even though it was made by Hermle.
Why old mechanical movements wear out
Over decades, the oil in a mechanical movement thickens and darkens, and the pivot holes in the brass plates wear into ovals. The pivots then pinch and the clock loses power. Cleaning and rebushing by a clock repairer can fix this, but some owners choose an identical new movement instead.
Sellers of new movements argue that a direct replacement of the same model is quicker than an overhaul and usually fits the existing weights, pendulum and hands. Repairers, on the other hand, point out that an original movement adds to the value of an antique clock. For a family heirloom or a collectible, keep the original movement and have it repaired.
See also: finding a clock repairer for a mechanical movement on OnlineClock.app.
How to measure for a replacement quartz movement
The most important measurement is the dial thickness. Esslinger, a long-running clock parts supplier, says the threaded part of the shaft must pass through the dial and leave about an eighth of an inch of thread for the nut. Measure from the top of the shaft down to the movement box for the total length, and leave room for the hands and cap nut if there is glass in front.
Esslinger also says there is no reliable way to cross-reference quartz movements by number, so measuring the old shaft is the safe method. Check that the hole in the dial is wide enough for the shaft, and that the holes in your hands match the new shaft's size and shape before reusing them.
See also: a step-by-step guide to swapping a quartz movement on OnlineClock.app.
Standard or high torque
A standard quartz movement only has the strength to turn light, short hands. Long or heavy hands need a high-torque movement, otherwise the clock may stop or lose time, especially as the hands climb from six to twelve.
Suppliers draw the line differently. One Australian parts shop strongly recommends high torque once the minute hand is longer than 160 mm, measured from the center of its hole to the tip. Esslinger mentions high-torque movements for big clocks with long hands, and suggests larger batteries for long-hand builds. When in doubt, check the limit stated by the maker of the movement you buy.
Questions people ask
Can a quartz clock movement be repaired?
Usually not. Its gears are sealed in, so after checking the battery and contacts, the normal fix is to replace the whole movement with one of the same shaft length.
How do I know what shaft length I need?
Measure the dial thickness, including any mounting washer. The threaded part of the shaft should pass through and leave about 1/8 inch of thread for the nut.
What do the numbers on the back of my clock movement mean?
On many German mechanical movements they identify the model and, on pendulum clocks, the pendulum length in centimeters. Two separate digits often show the year of manufacture.
When do I need a high-torque movement?
When the hands are long or heavy. One supplier recommends it for any minute hand over 160 mm; others set their own limits.
Keep exploring
Sources
- How to determine a quartz clock movement's shaft size, Esslinger
- High torque movements, The Clock Shop (Australia)
- Why order a movement?, Clockworks
- Clock movements FAQ, Timely and Timeless
More clock guides
How to identify an antique clock and judge its value · Clock hands and numbers · Grandfather clock weights, winding and care · Why clocks use IIII instead of IV · Tempus fugit: the motto on the clock · How to date a watch by its serial number · The Westminster chime · all guides