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I wrote before about the Timesavers 15959 clock mainspring, specified as 3/4 by 0.0165 by 120 inches. My latest batch of these springs are different: they have a copper rivet and the loop is formed from the spring itself (i.e., not a separate piece). Also, the spring is thinner, the one I used is 0.0153 inch thick, which is plenty strong enough for many antique American clocks. I used it for the time mainspring in a Sessions black mantel clock.

Below are photos of variations on the 15959 mainspring I have received:

• Left: 0.0145 inch thick, labeled 37 on the loop;
• Center: 0.0165 inch thick, labeled 42 on the loop;
• Right: 0.0153 in thick (only one example measured so far), copper rivet.
• Bottom row: A Sessions black mantel clock in which I installed the 15959 mainspring with copper rivet. I installed the spring in the time train, and it provides plenty of power.

Repair job 5921. Installed 14 bushings, replaced the damaged time mainspring (Timesavers 15959 with copper rivet, 0.00153 inch thick), re-pinned one pinion, replaced the click on the time mainwheel. The original time mainspring was 0.0176 inch thick (but the replacement needs to be thinner). The original strike mainspring is 0.172 inch thick.

The clock is 10 7/16 inches tall and 18 inches wide. The minute hand is 2 1/8 inches long.

See more photos.

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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.

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I repaired this Seth Thomas shelf clock and installed new mainsprings because they had previously been replaced with springs that were too strong.

The case is 22 3/8 inches tall and 14 3/4 inches wide. The minute hand is 2 13/16 inches long. I replaced the dial because the original was in very bad condition. Note that the door is not present in the photos below (the customer didn’t send it with the clock to prevent breaking the glass).

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Repair job 5726.The movement is marked “8 1/4″ on the lower front. Later, Seth Thomas named this movement No. 89. It is an efficient running movement due to its deadbeat escapement.

I polished the pivots and installed bushings. The mainsprings in the clock when I received it were as follows:

Time: 3/4 x 0.0178 inches, Strike: 3/4 x 0.018 inches.

I installed thinner new springs to make the movement have a longer life. They are no. 77.303 from R & M Imports. They are made of beautifully blued steel, of the following dimensions:

• Time: 3/4 x 0.0161 x 120 inches
• Strike: 3/4 x 0.0162 x 120 inches

These thinner mainsprings will reduce future wear to the time and strike mainwheels.

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My customer sent this movement to be repaired, because the clock fell off the wall, bending the center arbor and causing 2 gears to come out of the movement plates.

The movement has the nice thin original Seth Thomas mainsprings.

Time Mainspring: 11/16 inch wide by 0.0165 inch thick.

Strike Mainspring: 11/16 inch wide by 0.0154 inch thick.

See more photos.

Repair job 5539. I polished the pivots, rebuilt the pinion on the third strike gear, and installed 10 bushings. The movement might not be original to this case (the mounting feet are bent way back in an attempt to move the movement forward in the case).

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Over the past three years, I’ve posted about mainsprings for antique American clocks. I started with a post on June 12, 2007 about a mainspring from Merritt’s Antiques.

Most clock parts distributors offer a “standard” American loop end 8-day mainspring 3/4 inch wide by 0.018 inch thick and 96 inches long. These springs are too strong! They may cause severe wear to the clock’s mainwheel teeth. A thinner mainspring about 0.0165 inch thick should be used instead. (Regarding mainspring replacement, I believe that the original mainsprings should be kept in an American antique clock unless a spring is broken, damaged or too strong. Notice that I said “too strong” – the old mainsprings are almost never too weak!)

Several clock parts suppliers offer the thinner mainsprings for American clocks, typically 3/4 x 0.0165 x 96 inches. Clock repairers have noted inconsistencies in these springs – the thickness and strength can vary from batch to batch. I recently bought springs from 3 suppliers to test. For each spring, I measured its thickness, and its diameter when first removed from its retainer. On some springs I also measured the diameter after being fully wound and unwound 2 times.

The measurements are given below, with the mainsprings placed in categories based on my recommendations. At times, a supplier will ship mainsprings from a different source. The mainspring types pictured below show the appearance of the springs that I measured.

Recommended Standard Length Springs – 96 Inches Long

Timesavers 18790, Specified as 3/4 x 0.0165 x 96 Inches

Sample 1) 0.0165 inch thick, opens to 10″ (this spring has some rust on the outside and will be exchanged for another.)

Sample 2) 0.0162 inch thick, opens to 11.5″

R & M Imports 77.308, Specified as 3/4 x 0.0165 x 96 Inches

Sample 1) 0.0160″, opens to 11″, 9.5″

Sample 2) 0.0160″, opens to 11.5″

Sample 3) 0.0160″, opens to 11″

Sample 4) 0.0158″, opens to 13″

I have been using this spring from R & M for years. Typical batches from 4 – 5 years ago measured 0.0165 inch thick. There was a batch about 2 – 3 years ago that had brittle inner ends that broke easily. Current springs seem fine in this regard.

R & M Imports 83065, Specified as 3/4 x 0.0165 x 96 Inches

Sample 1) 0.0160″, opens to 11″, 9.5″

This sample is identical to the above spring (R & M 77.308) and costs over twice as much, so there is no reason to buy it!

Merritt’s Antiques P-1496, Specified as 3/4 x 0.0165 x 96 Inches

New springs purchased May 2010:

Sample 1) 0.0159″, opens to 12″, 11″

Sample 2) 0.0161″, opens to 12″, 10″

I first used this mainspring 4 – 5 or more years ago. Some batches have been significantly thinner than others. A batch that that I purchased in October 2008 is packaged the same as this current batch. The springs  have the following measurements:

Sample 1) 0.0165″, opens to 11″

Sample 2) 0.0165″, opens to 11″

Sample 3) 0.0158″, opens to 11″

Sample 4) 0.0165″, opens to 9″, 8″

Sample 5) 0.0165″, opens to 11″

Sample 6) 0.0156″, opens to 11″

An older batch with plastic inner wrap had thinner springs:

Sample 1) 0.0157″, opens to 11″

Sample 2) 0.0155″, opens to 11″

Another old batch (probably 4 – 5 years old) marked “Anchor” on the plastic inner wrap contained mainsprings that were very thin:

Sample 1) 0.0135″, opens to 10″

Sample 2) 0.0140″, opens to 12″

Around June 2007, Merritt’s was shipping a different mainspring under this part number. It was the same as the R & M 77.308 and the Timesavers 18790.

Recommended Long Springs

Timesavers 15959, Specified as 3/4 x 0.0165 x 120 Inches

Sample 1) 0.0160″, opens to 12″

Sample 2) 0.0168″, opens to 13″

120 inch long mainsprings are sometimes recommended for more uniform timekeeping over a one week running period. I have had excellent results with the 96 inch long springs, however, and recommend them for most movements.

Springs That Are Very Strong

Merritt’s Antiques MS309, Specified as 3/4 x 0.0165 x 96 Inches

Sample 1) 0.0158″, opens to 15″, 13″

This is the type of spring made in Germany that is very springy. The package has a yellow label saying “Beco Technic Germany”. They are tempered to a straw color instead of blue like many other springs. I don’t like to use these in average American antique clocks, as they provide more power than necessary.

Merritt’s Antiques MS310, Specified as 3/4 x 0.0165 x 108 Inches

Sample 1) 0.0152″, opens to 21″, 18″

This spring is by Beco Technic Germany just as the above spring. It is intended for the Seth Thomas No. 89 movement. It may be stronger than necessary, and I prefer to use springs in the first or second categories above instead.

Springs That Are Very Weak

Merritt’s Antiques P-1956, Specified as 3/4 x 0.0165 x 96 Inches

Sample 1) 0.0165″, opens to 6″

Sample 2) 0.0165″, opens to 6″

Springs in this batch open out to only 6 inches when released from their clamp. They are not very springy and are too weak for most American antique clocks.

The springs in my first batch two years ago were excellent! They opened out to 11 – 12 inches when released from their clamps, and provided plenty of power. I used these springs in several clocks. But batches received last fall and later have been very weak. So I don’t routinely use these springs anymore.

Other Springs

Timesavers 29515, Specified as 3/4 x 0.016 x 108 Inches

Sample 1) 0.0153″, opens to 28″, 20.5″

This spring seems way too powerful. Also, the surface is not smooth and the spring has a rough action.

Conclusions and Recommendations

For American antique clocks, I keep original mainsprings in the clock unless there is a good reason to change them. For replacements, I prefer springs from the first category (Recommended Standard Length Springs – 96 Inches Long). Many typical Seth Thomas, Ingraham, Gilbert, Sessions and New Haven clocks can use these springs.

Ingraham mantel clocks with deadbeat (or almost-deadbeat) escapement can use a somewhat thinner spring for the time side of the movement.

Some Waterbury and Ansonia movements made from the 1880′s through the 1920′s originally had mainsprings 0.0145″ to 0.016″ thick. It is important to select the proper thinner spring for these clocks.

It is best to measure and label new mainsprings when you receive them. After a time you can build up a stock of normal, thicker and thinner springs, so you can choose the proper mainspring when a mainspring does need replacing.

I believe that routine mainspring replacement should be avoided in antique American clocks.

Thanks to Len Lataille for encouragement to measure these mainsprings.

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This Schatz 400 day clock came into my shop for repair. The customer told me that it had a broken mainspring. On disassembly, I found that the mainspring was broken in more than 15 pieces! (Normally, a mainspring has just one break). See photos below:

What caused the spring to break into multiple pieces?

The clock had been cleaned without being dismantled (there was debris in the gears from incomplete cleaning). The cleaning fluid could not be rinsed out of the mainspring. The fluid attacked the steel, causing stress cracks to form, followed by breakage.

Repair job 5176. Back plate number 1278, no date. Uses 0.004 inch suspension spring. When the mainspring broke, it bent the front second wheel pivot. I inserted a new pivot, and polished several other pivots.

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Two years ago, I wrote about the P-1956 mainspring from Merritt’s Antiques. This spring was ideal for many antique American clocks.

My newest batch of these mainsprings (received late in 2009) are weaker than the first batch I had. When removed from their clamp, they open out to only 5 1/2 inches (my first batch opened to about 11 inches).

These springs may be too weak for clocks with a recoil escapement. I still need to test them in a Seth Thomas No. 89 movement.

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I recently repaired a Seth Thomas Adamantine mantel clock made around 1905. It has a No. 89 movement. This movement is very efficient in operation, due to the use of a deadbeat escapement. Even with a thin time mainspring, these movements typically take an excellent escapement motion.

This particular example has thin, original mainsprings.

Time Mainspring: 3/4 x 0.0167 inch.

Strike mainspring: 3/4 x 0.0163 inch. (Unfortunately, I had to replace the strike mainspring because it had a rough action when nearly wound, typical of springs that may break soon. I used a new Merritt’s Antiques P-1956).

Many examples of the No. 89 movement have thicker springs, quite often around 0.0175 inch thick, sometimes thicker. After proper repair, this movement will run well with thin springs.

Here is a video of the escapement motion, first run down 6 1/2 days, then fully wound:

Repair Job. 4970.

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