Working on a 400-day torsion clock is an exercise in patience
These clocks don't run on a traditional seconds pendulum. The bob is suspended from a thin ribbon of steel that twists back and forth horizontally, completing a full rotation every four seconds or so. The name comes from the idea that it runs for 400 days on a single winding, though realistically you're looking at maybe 300 to 350 if the movement is healthy and the environment is stable. I've spent more years than I care to count taking these apart, cleaning them, and putting them back together without breaking something I can't fix. Start by removing the clock from its case. Most 400-day movements are mounted on a base plate with the dial attached to a separate frame. Gently lift the movement out by sliding it forward off the mounting posts at the bottom. Don't force it. The posts are usually tapered brass or steel pins that sit loosely but can be stubborn if decades of grime have welded them in place. Work them side to side, not up and down. Once the movement is out, remove the glass dome first, then the bob assembly. The bob hangs from a guide rod that runs through a fork at the top of the movement. There's typically a small retaining clip or a friction fit collar that holds the guide rod in place. Slide it off carefully. The torsion spring is inside the pendulum bob itself — that coiled ribbon of special steel is the entire energy storage system for this clock. It's the most delicate part and the part most people ruin.
Disassembly and inspection
Remove the dial by lifting it off its posts. Underneath you'll find the mainplate with the gear train. There are typically five or six wheels depending on whether the clock has a seconds dial or calendar complication. The going train — the one that transfers power from the mainspring to the escape mechanism — is what matters most. The escape wheel on these clocks is tiny, often no more than 12 millimeters in diameter, and the teeth are finer than embroidery thread. When I took apart a Seth Thomas model 40 in 2019 that had been sitting dead for about twelve years, I found the pivot on the fourth wheel had worn a deep groove into the mainplate. Not the jewel — the brass mainplate itself. The clock ran fine until someone tried to wind it past the natural stop, which happens when the mainspring barrel hits its internal limit. That one mistake can tear through a movement in minutes. I replaced the fourth wheel and installed a synthetic ruby jewel in the plate using a micro pin vise and a drop of slow-curing epoxy. Took about forty-five minutes and the clock has been running solid since. Inspect every pivot for wear, every bushing hole for ovalization, and every tooth on every wheel for chips or flattening. The pallet forks on the verge escapement are especially vulnerable. A bent fork will cause the torsion pendulum to lose amplitude and the clock will stop within hours instead of days.
Cleaning the movement
Ultrasonic cleaning works well for steel parts but you need to be careful about bronze and brass. Long exposure to some ultrasonic solutions will dezincify brass over time. I use a warm solution of warm water and a few drops of dish soap for routine cleaning, and a dedicated brass-safe ultrasonic solvent only when necessary. Leave parts in for ten to fifteen minutes maximum. Rinse in distilled water and let them air dry on a clean paper towel. Never blow compressed air across pivots — the force can bend them. The torsion spring inside the bob needs special attention. Do not submerge it. The coiled ribbon spring can absorb moisture and then oxidize from the inside out, which weakens it permanently. Wipe it gently with a lint-free cloth dampened with naphtha or light mineral spirits. Let it dry completely before reassembly. If the spring looks discolored or has any visible pitting, replace it. I've seen springs that looked fine on the surface but had lost significant tension due to internal stress relaxation. A tension tester costs about eighty dollars and saves you the guesswork.
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Reassembly and regulation
Start with the mainspring. Remove the old spring from the barrel arbor using a spring hook or a properly sized slotted tool. Wind the new spring onto the arbor carefully — it wants to fly apart. A mainspring that binds inside the barrel will cause irregular running or complete stoppage. The key here is clean hands, good lighting, and taking your time. This step accounts for probably half of all failed repairs I've seen. Reassemble the gear train in reverse order of disassembly. Apply a tiny amount of clock oil to each pivot hole — I use Moebius 9010 for the lighter oil and Moebius 9100 for the heavier positions. The pallet point gets a microscopic amount of Moebius 9500 or a similar dedicated pallet oil. Any more than a pinpoint and you'll attract dust and create drag. Any less and the oil will migrate away within weeks. Once the movement is reassembled, reinstall the torsion spring into the bob. The spring has two ends — one attaches to the arbor inside the bob and the other to the outer case. Wind it exactly four to five full turns. More than that and you risk overstressing the metal. Fewer than four and the clock won't have enough energy to sustain the torsion oscillation through the gear train resistance.
Hang the bob on the guide rod and set the beat. This is the part that separates people who can fix these clocks from people who can't. With the torsion pendulum, "beat" means the pallets should engage the escape wheel teeth symmetrically when the bob is at the center of its swing. Listen for a consistent ticking on both sides of the rotation. If one side is louder or missing entirely, the pallet depths are uneven. Adjust by carefully bending the pallet arms with a pair of fine tweezers — millimeter movements matter here. I've adjusted pallet depth by as little as 0.2 millimeters and watched a dead clock come back to life. Regulation is done through the regulator lever, usually located at the back of the movement near the pendulum suspension. Moving it one click changes the effective length of the torsion spring by a fraction of a millimeter. You'll gain or lose maybe ten to fifteen seconds per day per click. It takes patience. Set the clock going, mark the time against a reference, and let it run for at least twenty-four hours before making another adjustment. The rate will settle differently depending on temperature and humidity in the room where it's installed.
Common problems and what they actually mean
If the clock runs for a few days and then stops, the mainspring is likely dirty or partially broken. Remove it, clean the barrel, and inspect for cracks. A broken spring will have snapped cleanly with a sharp edge visible under magnification. If the clock runs but loses time rapidly, check the pallet engagement. The escape wheel should turn freely when you manually rotate the torsion pendulum — any binding means something is misaligned or a pivot is dragging against the plate. If the bob wobbles or touches the guide rod, the suspension spring at the top is bent. This is common after shipping or if someone jostled the clock. Straighten it carefully or replace the suspension assembly. A bent suspension will cause the pendulum to drift off center and the clock will stop within a day or two.
There's a limitation worth noting upfront: these clocks are sensitive to placement. A 400-day clock placed on an uneven surface, near a heating vent, or in a room that sees regular foot traffic will struggle to keep consistent time regardless of how well it's repaired. The torsion pendulum responds to vibration the way a liquid level responds to a nudge — small disturbances compound quickly. If you're repairing a clock for someone who wants it to keep excellent time, tell them upfront that placement matters more than anything else you do in the shop. No amount of perfect regulation will overcome a bouncy shelf. For parts, the main suppliers are Klockars, Howard W. Smith & Associates, and a few specialized parts dealers in Germany and Japan. Authentic mainsprings for vintage movements are hard to source in exact dimensions. I've successfully used metric equivalents from watchmaking suppliers when original clock spring sizes aren't available, but you need to match both the width and the thickness precisely. A spring that's even 0.05 millimeters too thick will over-wind the barrel and stress the train gears. If the movement is beyond repair — which is more common than you'd think with these clocks, especially the cheap import models from the 1970s and 80s — replacing the entire movement assembly is sometimes the only practical option. New replacement movements run about two hundred to four hundred dollars depending on the style, and while they won't have the same aesthetic appeal as an original movement, they'll keep time reliably for years. I recommend this path when the mainplate has multiple worn bushing holes or when the verge escapement components are cracked or missing. At that point you're spending more on reproduction parts and labor than a new movement would cost.
Keep a notebook. Write down the model number, the serial number, the current rate, the ambient temperature, and what adjustments you made. Three months later when the same clock comes back with the same problem, you'll thank yourself for the record. I still have notes on a 1920s Ansonia I worked on in 2008, and they were still useful when it came back in 2022.
