Many antique American clocks have mainsprings that are stronger than necessary. The most popular replacement mainsprings are even stronger than the originals. These strong replacement springs cause wear to the main wheel teeth and pivot holes. Thinner mainsprings are available, and should be used to replace old replacement springs that are too strong.
Here is an Ingraham oak kitchen clock made in 1903:
The oak case is 21 7/8 inches tall and 14 11/16 inches wide. The movement has a date stamp of 6 03 (June 1903). The label on the back of the clock gives the model name “Oneida”.
The owner had it repaired 30 years ago. After repair, the time side of the clock was hard to wind, but the repairman assured him that it was OK.
When I looked at the movement, I saw excessive wear in the front time second wheel pivot hole (the steel pivot should be centered in the hole):
The time mainspring is labeled ”Usibel France” and is extremely strong, making the clock hard to wind and causing wear. These springs can be identified by their logo and the shape of the loop end:
I took the movement apart and cleaned it. Here is the badly worn pivot hole (the hole was round when the clock was new):
For comparison, here is another pivot hole with a small amount of wear:
Here is how worn the time main wheel teeth are:
10 more years of use with this strong mainspring might have worn off the tips of the teeth!
The strike second wheel teeth have less wear:
Replacement mainsprings are available that are thinner than the original mainsprings. Many American antique clocks are over-powered, and can run on weaker mainsprings. I proposed installing thin mainsprings to my customer, and he agreed. The video below shows that the clock runs and strikes very well with these thinner mainsprings:
Here is the movement after I repaired it:
Technical data
Repair job 5905. This is a common Ingraham 8-day time and strike pendulum movement. It has an American-style strip recoil escapement.
The Usibel mainspring is 0.0185 inch thick. The original strike mainspring is 0.0172 inch thick. The mainsprings I installed are 3/4 inch wide, 120 inches long, and about 0.0145 inch thick. They are part number 15959 from Timesavers, but are the thin version (0.0145 inch thick, identified by “37″ stamped on the loop end instead of “42″) that were sent to me instead of the regular version (0.0165 inch thick). The actual thicknesses that I measured are:
- Time spring – 0.0140 inch;
- Strike spring – 0.0148 inch.
The time mainwheel teeth have about 50% wear, and the strike mainwheel teeth are about 20% worn. With these thin mainsprings, I expect little future wear to the mainwheel teeth. The movement runs fine with the worn teeth.
I installed new pins in 3 pinions (T3, T4 and T5), polished the pivots, and installed 16 bushings.
Mainspring Strength
The force a mainspring provides is proportional to its thickness cubed. Thus, the 0.0185 inch thick mainspring provided 2.3 times the force that the 0.0140 inch mainspring provides. (The 2.3 is approximate, because there are other variables such as the temper and composition of the metal).
Unfortunately, 0.0145 inch thick mainsprings (3/4 inches wide) aren’t as readily available as 0.0165 inch thick springs.
See my post Ansonia Walnut and Oak Kitchen (Shelf) Clocks for more about Usibel mainsprings.
Conclusion
The time mainspring that is too strong has been replaced with a spring thinner than the original. The original strike mainspring has been replaced with a thinner mainspring. The clock runs well and will not wear nearly as much in the future. It will be a family heirloom that can be enjoyed for many years.
