The owner had attempted to install a new mainspring himself, and ended up with the tangled mess in the first photo below! (The tangled mainspring is the original strike spring, which is good and was retained in the clock, the time spring (which was broken) is not present in the photo.

The replacement time mainspring spring is a Timesavers 20506 11/16 x 0.0165 x 96 inch spring that actually measures 0.0157 inch thick and 23/32 inch wide. This spring opened out to 12  inches diameter when first released from its clamp. The original strike mainspring is 0.016 inch thick and exactly 11/16 inch wide.

Below is a movie of the movement striking. It strikes hours using the countwheel strike mechanism:

Here is a movie showing a closeup of the escapement and general views of the movement:

Repair job 5109. Besides installing the new time mainspring, the pivots were polished, 7 bushings installed, and some adjustments made to the striking.

In the past, someone coated the time second wheel with solder (visible on the right in the photos below). I have no idea why they did this. My customer and I decided it was not worthwhile to try to remove the solder. The dial is not shown because all of the paint has come off and it has had a paper face applied.

This movement has 4 wheels in the time and strike gear trains, and uses 11/16 inch wide mainsprings. I installed a new time mainspring 11/16 wide by 0.0165 inch thick by 96 inches long from Empire Clock. This spring opens out to about 9 inches when first released from its clamp. The movie below shows the escapement motion with the spring fully wound. The motion is good but not excessive.

I installed a new strike mainspring also, Timesavers 20506 11/16 x 0.0165 x 96 inch. (This spring opened out to 22 inches diameter when first released, but opened out to 13 inches after 2 winds.) I replaced both mainsprings because the originals were rusty.

Repair job 5072. Needed the pivots polished, 13 bushings installed, the escape wheel teeth trued, replace the wires in pinion T4, reverse the wires in pinion T3, smooth and polish pallets. No oil on the pallets.

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 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.

Gilbert / 1807 / Made by Gilbert in Winsted, Conn., U.S.A.

The following movie shows the bim-bam striking:

The movement needed a lot of pivot polishing. The train pivots had moderate wear. The mainwheel pivots were very rough, and had probably left the factory this way!

The original 0.0175 inch thick strike spring was broken. The time mainspring was a previous replacement that was too strong: a Usibel France 0.o0183 inch thick. I installed the following new mainsprings:

• Time: R & M 83065 (same as their 77.308) 3/4 x 0.016 x 96 inches
• Strike: R & M 77.308 3/4 x 0.0165 x 96 inches

The following movie shows the escapement motion when run down 8 1/2 days and when fully wound:

Repair job 5017.

The clock pictured here has an oak case and 8-day time and strike movement. The paper dial is a replacement. Height 37 1/4 inches, width 13 1/2 inches, the minute track was about 7 inches in diameter on the original dial.

Job 5005. This clock has both original mainsprings.

• Time: 3/4 wide by 0.0168 inch thick
• Strike: 3/4 wide by 0.0175 inch thick

It has the larger, older type movement with 5 7/8 by 3 5/8 inch plates. The plates are 1.45 millimeters thick.

This clock movement is known for running on thinner than average mainsprings. Even with the weaker springs, there was major wear to the pinion wires (some were cut 1/3 of the way through)! I replaced the wires in 4 of the pinions. On the other four pinions, I reversed the wires to bring an unworn surface into operation. The pinion wear was caused by 2 factors:

• The gears are quite narrow, concentrating the force in a small area;
• The clock may have been spray oiled. When oil is on the gear teeth, dust sticks to the teeth and becomes embedded, and acts as an abrasive, cutting away the harder steel pinion material.

The pivots and pivot holes had a typical amount of wear. I polished the pivots and installed 12 bushings.

A weakness of this and some other Waterbury movements are the flat steel clicksprings on the mainwheels. They commonly break. On this clock they were still intact, but the one on the time side looked about to break. I replaced both of them with round steel wire clicksprings. See the photos below.

This movement runs well with thin mainsprings. Both springs in this clock are original:

• Time mainspring: 3/4 inch wide by 0.0155 inch thick;
• Strike mainspring: 3/4 inch wide by 0.0165 inch thick.

Here is a movie of the movement and the clock striking:

Here is a movie of the escapement motion with the clock fully wound and run down 9 days:

Repair job 4879. The mainsprings are original, are not too strong, and operate smoothly, so I kept them in the clock.

The one-day time and strike spring-driven movement is stamped “C. Jerome / New Haven Conn / USA”. The label on the rear of the case says “CHAUNCEY JEROME / MANUFACTURER OF / EIGHT AND ONE DAY / BRASS CLOCKS / TIMEPIECES AND MARINE LEVERS / New Haven, Conn. / AMERICA”

The case is 13 9/16 inches tall and 10 1/8 inches wide at the base. The dial time track is 5 inches in diameter. The minute hand is not original (but appears to be a very old replacement), the original was a small spade matching the hour hand.

The dial had been poorly touched up in the past, so I had it repainted as close to original as possible by The Dial House. I cleaned the movement, polished the pivots, installed 8 bushings, straightened 3 teeth and replaced one tooth in the strike second wheel, polished the pallets, and made a new verge retainer.

The movie below shows the movement of the clock and shows the hour striking in operation:

Below is a slide show of more photos:

I installed two new mainsprings, 5/16 x 0.0137 x 45 inches (part number PM-CS510 from The P.M. Company). These springs are thin to reduce wear in the movement, but will power the clock for 3 – 4 days on a winding. The movie below shows the escapement motion:

The movement plates are 1.9 mm thick. Later Connecticut clocks have thinner plates. For example, a Seth Thomas No. 89 movement I measured has 1.4  mm thick plates, and a 1920s Ingraham movement has 1.25 mm thick plates.

Repair job 5081.

The case is 18 1/8 inches wide at feet, 11 1/16 inches tall, with 4 1/4 inch time track on dial.

Below is a slideshow of more photos:

Here is a video of the clock striking:

Here is a movie of the escapement action, first run down 7 days, then fully wound:

Repair job 5094. No. 89T 8-day time and bim-bam strike movement.The time mainspring is a 3/4 x 0.0172 x 96 inch mainspring from R & M Imports (opened to 8 inches when unclamped. The time spring was original, but I replaced it because it had a squeaky and jerky action which sometimes indicates it will break soon. This movement needs a slightly stronger time mainspring than the regular No. 89, as the half-hour strike hammer is lifted through a great distance. The strike mainspring is the original (marked ST) 3/4 x 0.0165 inch spring. It opened out to only 6 inches in diameter when uncoiled, yet provides plenty of power to operate the striking for over 8 days.

The case is 19 3/4 inches wide and 9 1/4 inches tall. The dial has a 4.5 inch time track, and is aluminum with embossed and painted numerals.

The movement has the original mainsprings that still open up very far and provide plenty of power. They are 3/4  inch wide loop end springs. The thicknesses are:

Time mainspring: 0.017 inch

Strike mainspring: 0.0167 inch

Job 5146. I had last repaired this clock over 10 years ago, and it just needed to be disassembled and cleaned to make it run well again.

This example looks similar to that in the photo labeled “1924″ in Tran Duy Ly’s Seth Thomas clock book. The case is dark mahogany, 31 inches tall, 15 5/8 inches wide, and the dial has a 10 3/4 inch time track. The movement is 8-day time only, no. 123 E. I first overhauled this clock in 1999 (polished pivots and installed 5 bushings). It ran until 2009, when the click broke (an uncommon occurrence).

I cleaned the movement and did the following repairs:

• Installed a new click;
• Installed a new mainspring, as the old one had a squeaky action even after cleaning and oiling. I installed a Merritt’s P-1956 3/4 x 0.0165 x 96 inch mainspring (the new spring opened up to 5 1/4 inch diameter after being wound and unwound 5 times).
• The pivots, which I had polished during the last overhaul, were still in excellent condition.

This movement has stopworks for the mainspring, I set it up so that it stops the winding when the spring is one turn from being fully wound. The case has a beat plate, and the motion of the pendulum measured on the plate is as follows:

• Escape arc:  + and – 0.75 degrees
• Wound up: + and – 3.3 degrees
• Rundown 3 days: + and – 3.2 degrees
• Rundown 7 days: + and – 2.8 degrees

The paint on the dial was flaking badly, and the customer wanted it restored. I had it repainted by The Dial House in Dallas, Georgia.

Here is a slide show of the clock and its movement:

Repair job 1891.