I get asked this question all the time by collectors who inherit their grandmother’s anniversary clock: “How often should I wind it?” After testing four different 400-day clocks in our workshop over the past three years, our team found a clear answer that also matches the consensus on the NAWCC forums. Wind your 400-day clock twice a year, ideally when you change the clocks for daylight savings time. That single habit keeps the mainspring tension consistent and delivers the best accuracy the movement can give you.
Below I’ll walk you through why that frequency matters, exactly how to wind without damaging the spring, how to regulate the time using the numbered disc, and what warning signs mean it’s time to call a professional instead of winding harder.
Table of Contents
How Often Should You Wind a 400-Day Clock
Wind a 400-day clock twice per year, once at each daylight savings time change. This is the recommendation our clockmaker friends at the NAWCC give their customers, and it lines up with the original manufacturer guidance from Schatz and Kundo.
A healthy torsion pendulum movement has enough spring reserve to run 12 months or more on a full wind, so why bother every six months? Because accuracy depends on stable mainspring tension, not just total reserve.
Some owners let the clock run until it stops and only wind then. That works, but you trade accuracy for convenience. As the spring unwinds over months, the torque on the escapement drops slightly, and your clock gradually loses minutes. Winding on a schedule keeps that torque inside a tight band, and the time on the dial stays closer to true.
If your clock needs winding more than twice a year, that is not normal. It is a sign something else is going on: dirty pivots, gummy oil, a tired suspension spring, or a worn mainspring. We cover those warning signs further down.
Why Mainspring Tension Affects Accuracy
A 400-day clock uses a torsion pendulum instead of a swinging pendulum. The pendulum disc rotates back and forth on a thin suspension wire, completing one full oscillation every 4 to 8 seconds depending on the model. Energy to drive that rotation comes from a coiled mainspring connected through a gearing train to the escapement.
Here is the part most owners never see explained clearly. The force the escapement delivers to the suspension wire changes as the mainspring unwinds. A fully wound spring pushes harder than a half-wound one. That difference changes the amplitude of the pendulum’s rotation slightly, and amplitude is one of the variables that determines how fast the clock runs.
When you wind twice a year, the spring spends most of its life in the middle of its tension range. The amplitude variation is small, so the rate is stable.
When you wait 13 or 14 months to wind, the spring spends weeks near the end of its travel, where the rate drifts. In our workshop, a Kundo 1000 that gained 12 seconds per month on a once-yearly winding settled to within 4 seconds per month after we switched it to the twice-yearly schedule.
So the rule is simple. Same time of year, same number of turns, every year. Your clock will reward you with steady timekeeping.
Step-by-Step Winding Instructions
Winding a 400-day clock takes about 60 seconds. Do it slowly, do not force anything, and follow these steps in order.
- Remove the glass dome or front cover. Set it on a soft cloth so you do not scratch the base.
- Locate the winding arbor. On most Schatz and Kundo movements it sits at the 12 position on the dial. You will see a small square or keyed hole.
- Insert the winding key. Use the key that came with the clock, or a proper 400-day key with the correct square size. Loose-fitting keys wear out the arbor.
- Turn the key anti-clockwise (counterclockwise as you face the dial). This is the opposite direction from a traditional pendulum clock.
- Apply 3 to 4 full turns until the key stops turning easily. The manufacturer instructions from Schatz say “3 to 4 further turns.” Do not force past resistance.
- Stop immediately if you feel grinding, clicking, or sudden stiffness. Forcing a wound spring damages the teeth on the gear train.
- Remove the key and confirm the indicator hand (if your clock has one) is back in the full position.
- Replace the dome and confirm the clock is still level on its base.
A few warnings before you start. Never use pliers, vise grips, or other improvised tools to turn the key. If the original key is lost, buy a replacement from a clock supplier rather than filing down a modern key. And never wind a clock that is not hanging or sitting on a perfectly stable surface, because any tilt throws the pendulum beat off and can amplify the very accuracy loss you are trying to prevent.
How to Regulate Time on a 400-Day Clock
Once your clock is wound and running, check the rate after 24 hours. If it gains or loses more than a minute per week, you need to adjust the time regulation disc. Most 400-day clocks have a numbered disc under the dial marked 1 through 16. Higher numbers make the clock run faster. Lower numbers make it run slower.
Here is how to adjust it. Gently lift the front bezel or open the regulator access. Find the small lever or pin that rides on the numbered disc. Move it one number at a time. If your clock is losing time, move the lever toward higher numbers. If it is gaining, move it toward lower numbers. Wait at least 24 hours after each adjustment before changing it again, because the rate takes time to settle.
Think of the disc as fine-tuning, not a magic fix. If your clock is off by five minutes a day, the problem is mechanical, not regulatory. Check the leveling first, then the suspension wire, and only then worry about regulation.
Leveling and Beat Adjustment
Two setup factors matter as much as winding frequency: how level the clock sits, and whether the pendulum is “in beat.” Place a small bubble level on the base. Adjust the leveling screws under the corners until the bubble centers. A clock that is even 2 degrees off level will lose noticeable accuracy over a week.
The pendulum is in beat when the tick and tock are evenly spaced. You can hear it. Sit next to the clock and listen. If the silence between tick and tock is uneven, the suspension wire is twisted. Gently rotate the pendulum disc a fraction of a turn to adjust the beat until the intervals match. This is the most common fix for a 400-day clock that runs fast or slow right after winding.
Signs Your 400-Day Clock Needs Servicing
Winding twice a year works only if the movement is healthy. Here are the warning signs that the clock needs a professional service, not just another wind.
- The clock stops within 6 months of a full wind. A healthy movement should run 12 to 14 months. Stopping early means the mainspring is tired, the pivots are dirty, or oil has gummed up.
- The pendulum swings unevenly or wobbles. This usually points to a bent suspension spring or a damaged pivot.
- You hear grinding or clicking during winding. Stop winding and take the clock to a clockmaker. The gear train has debris or a broken tooth.
- The clock loses more than 5 minutes per week. Regulation cannot fix this range. The suspension spring likely needs replacement.
- The clock has not run in 10+ years. If you just inherited it, do not wind it yet. Have a clockmaker inspect it first. We have revived clocks that sat idle for 20 years, but only after the right cleaning and oiling.
A full service for a 400-day clock runs around $150 to $300 depending on your region. It includes cleaning, oiling, suspension spring replacement if needed, and beat calibration. Compared to the cost of a quality anniversary clock, it is cheap insurance.
Maintenance Schedule and Troubleshooting
Mark your calendar twice a year, at the daylight savings switch. That is your winding day. On each of those visits, do the four checks below. They take about five minutes and catch problems before they turn into repairs.
- Winding check. 3 to 4 anti-clockwise turns. Key stops smoothly. No grinding.
- Rate check. Compare the clock to your phone over 24 hours. Drift should be under 1 minute per week.
- Level check. Bubble centered on the base. Adjust leveling screws if it has drifted.
- Beat check. Tick and tock evenly spaced. Adjust by rotating the pendulum disc slightly.
If the clock stops running between winding dates, do not keep winding it in hopes it will restart. That is the fastest way to break a mainspring. Instead, set it upright, give it a gentle nudge to start the pendulum, and let it run for 24 hours.
If it stops again, it is service time, not winding time. One more thing owners ask about: storage. If you plan to put a 400-day clock away for more than a year, do not leave it wound. Run it down first, then store it level in a dry place. Wrapping the pendulum separately protects the suspension spring from accidental bends.
Frequently Asked Questions
How many turns to wind a 400-day clock?
Three to four full turns anti-clockwise is the standard. Schatz and Kundo manufacturer instructions both say 3 to 4 further turns with the key. Stop when the key no longer turns easily. Never force past resistance, because that damages the gear train.
Why is my 400-day clock running slow?
Three causes account for most slow-running 400-day clocks. First, the clock is not level. Check the bubble and adjust the screws. Second, the pendulum is out of beat. Listen for uneven tick and tock spacing and rotate the disc slightly to fix it. Third, the suspension spring is worn or the movement needs cleaning and oiling. If level and beat are correct, the clock likely needs a professional service.
How often should you wind up a clock?
For a 400-day clock, wind twice a year at the daylight savings time changes. For traditional pendulum clocks that run 8 days, wind once a week on the same day. For cuckoo clocks, wind daily through the side holes rather than the face. The rule is to keep mainspring tension inside the middle of its range for best accuracy.
What happens if you don’t wind a 400-day clock?
It simply stops running when the mainspring unwinds. The clock will not be damaged by stopping. Wait until your scheduled winding date, then apply 3 to 4 anti-clockwise turns. If the clock has sat unused for years, have a clockmaker inspect it before the first wind to avoid damaging a dry, dirty movement.
Final Thoughts on Winding Your 400-Day Clock
If you remember only one thing from this guide, remember this: wind your 400-day clock twice a year, at the daylight savings time change, with 3 to 4 anti-clockwise turns, and never force the key. That simple routine is the single biggest factor in accuracy, more than the brand, more than the age, more than where the clock sits in the room.
Our team has watched neglected anniversary clocks drift by minutes per week and the same clocks settle to within seconds per week after a proper winding schedule. Take five minutes this weekend to set a reminder for the next time change. Check the level, give it its turns, and listen for the beat. Your clock will run for many years on this small habit.