Clock Loop-End Mainspring Replacements

Loop-End MainspringDescriptionDamage AssessmentMeasuring the Mainspring

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Loop-End Clock Mainspring Description

Loop-End clock mainspring description would be a long flat spring with a loop on one end. The loop gets wrapped around a movement's outer plate pillar. In other words this is the type of mainspring you can see when you look at the movement. It is not contained in a barrel style container. If the spring is in a barrel and you cant see the actual spring, please see the hole end mainspring page instead.

If the mainspring is broken it will seem like its winding up when you turn the key, only to snap back again. So you end up just winding it forever with nothing happening. When the mainspring is broken they sometimes stick way outside the side of the movement. In extreme, the mainspring will break and cause the clock case get damaged. This is not as common and usually the clock case is fine.

How they come

These mainsprings come wound up with a tie wire around it. Usually they can be installed in the movement just as it comes, wound up. Once the movement is reassembled perfect, you can wind up the mainspring and cut that wire off of it. As mentioned in other sections, treat these things with respect and caution. Wear safety glasses when working with mainsprings and also gloves. Seriously, these things can punch you, wack you, cut you, and snap at you. Just use caution because they do pack a punch.

Repair service offers a repair service if you just want us to take care of it for you instead. It would be a movement restoration job and not just a mainspring swap. If you choose to go this route please email a picture of the movement. We will see the picture and quote for the work. Please email to [email protected]

- - The content of this web page and web site was written and copyright by James Stoudenmire of - It may not be used commercially without permission. - -

Clock Mainspring Break - Damage Assessment

When a mainspring breaks within a clock movement, it could cause damage. The damage could be within the movement itself or to the clock case. It is uncommon but sometimes even the sides of the wood case get damaged when a mainspring breaks.

As for the movement itself, we need to check the gear teeth and the gear arbors. The damage will be on the lower part of the gear train if anywhere. The teeth of the gear that the mainspring is on, its a good place to start. The next gear up is also a frequent damage area. As you go up in the gear train, to the smaller wheels, damage is unlikely. The force of the breaking impact happens in the lower wheels, typically the main wheel and the next one up.

Wooden clock case inspection

Be sure you can get the movement out with no further damage to the clock case. Check the condition of the case to be sure it does not need attention. It may need to be reglued or nailed together more secure as the impact of the spring breaking could loosen the boards.

Inspecting lantern pinions

Lantern pinions are the type of gear that is made of vertical wires instead of teeth. It would be the smaller side of the two intersecting gears and would be going up the train not down. The vertical wires within the circular brass bushings act as teeth instead of having a gear. The advantage is the wire will spin within the bushings and thus decreasing friction and wear. Not all clocks have lantern pinions, this would apply to some antique American time strike units only.

If the clock has lantern pinions it is possible that some pins have bent or broken off completely. It would happen on the next wheel up from the mainspring gear, or main wheel you could call it. The impact of the main wheel from the break jolts the next wheel up with such force the pinion cant withstand the impact often. These are not so easy to repair if the pin breaks, it requires the removal of the pinion and also the pinion dismantled to restore it. The gear or wheel you could say, comes out, the pinion removed via staking set, and repaired with the same steel rod size to make perfect again. If the pin is just bent sometimes it can be straightened again with needle nose pliers for a quick fix.

Checking arbors and pivots

Damage assessment to the arbor of the next wheel up from the main wheel is also something to check. Often it will be bent from the impact of the mainspring breaking and would need to be straightened again if possible. Best to remove it and roll the arbor's long side on the table and see if it rolls straight. Also and just as important check the skinny ends of the arbor known as the pivots. These are the skinny ends of the arbor that stick into the movements outer main brass plates. If these are bent, the clock will not run. They need to be straight or the clock will have too much resistance in the gear train for the clock to function under the power of the new mainspring.

The teeth of the gear wheels

Lastly inspect the teeth of the gears on both the main wheel where the spring was attached, and the next wheel up. Bent teeth are common but not as easy to correct. Bending back and reshaping them with a needle file sometimes works, other times the wheel needs a chunk cut out and replaced with new teeth or dentures you could say i guess, soldered in place.

To much information

If this is not in the realm of your interest in learning about and experimenting with, please send us the movement instead. We will take care of everything for a fee. Please email a pic of what is going on to [email protected] so we can quote.

- - The content of this web page and web site was written and copyright by James Stoudenmire of - It may not be used commercially without permission. - -

Clock Loop-End Mainspring Measuring

Loop end mainsprings are measured by width, thickness, and length. These are not always easy measurements to get, and the mainspring would need to be removed from the clock. It can be a frustrating puzzle to do, and a dangerous one also. But if your learning clock repair or have time on your hands so to speak, here are some guidelines.

Caution !!

Always wear gloves and safety glasses when working with mainsprings. They can cut or punch the person working on the clock so please treat them with respect. It is not uncommon for the mainspring to break or shatter while working with them. Just treat them with caution and respect while protect your hands and eyes. Be aware if a mainspring is wound up or stretched way out to measure it, it has a lot of snapping power. These things can hurt when they smack your hand or fingers, and I would not want to even think about what it can do to an eye.

Getting the thickness and width

Items needed for this measurement is a tape measure and a digital caliper, these are the best things to use. To get the width of the mainspring is easy, just use the digital caliper in inches and see how wide it is first. When you have the width, find that width section first on the below chart. Next is the thickness, again using the digital caliper. Write these two measurements down and again refer to the chart and narrow down the section even more. Now you have a narrow section of the chart of sizes your working with and only need the length.

Measuring the loop-end mainspring length

The length is the hardest to get the measurement on. What we do here is put the end of the spring in a vise and stretch it out. We pull the spring straight with a tape measure beside it as we unwind it. Of course the tension of the spring is such it wants to wind back up in a violent manner. When the spring is let go it winds back up with a snap. This is the sort of stuff that I was cautioning about earlier, if no gloves it can cut. If there is a cat sitting by the vise and you let go, the cat may not like you anymore. The length is the hardest to get but close enough is ok. The length has not much to do with the function of the clock, only the time in which the clock will run. For example if the mainspring substantially shorter, it may not run the full 8 days.

The most common size loop end mainspring for antique 1900s through 1945 American units is CML304. This size was sort of the industry standard when Seth Thomas, New Haven, Gilbert, Sessions was in full swing with the 8 day time strike units in mass production.

- - The content of this web page and web site was written and copyright by James Stoudenmire of - It may not be used commercially without permission. - -

Loop End Mainspring
LESPRING: $14.89$49.89

Loop End Mainsprings Measurements to item #

WIDTH inch | mm THICKNESS inch | mm LENGTH inch Item #
1/8" 3.2 .010" | 0.25 19" CML 245
9/64" 3.6 .009" | 0.23 25" CML 246
5/32" 4 .009" | 0.23 26" CML 247
3/16" 4.8 .012" 0.3 31" CML 252
3/16" 4.8 .016" 0.41 54" CML 253
13/64" 5 .0105" 0.26 25 1/2" CML 254
7/32 5.6 .011" 0.28 24" CML 255
7/32 5.6 .017" 0.43 30" CML 256
1/4" 6.4 .010" 0.25 26" CML 257
1/4" 6.4 .012" 0.31 41" CML 259
1/4" 6.4 .013" | 0.33 24" CML 260
1/4" 6.4 .016" | 0.41 54" CML 261
9/32" 7 .009" | 0.23 30" CML 262
9/32" 7 .012" | 0.3 27" CML 263
9/32" 7 .012" | 0.3 30" CML 264
9/32" 7 .017" 0.43 48" CML 265
19/64" 7.5 .015" 0.38 39" CML 266
5/16" 8 .009" 0.23 20" CML 267
5/16" 8 .009" 0.23 36" CML 268
5/16 8 .010" 0.25 30" CML 269
5/16 8 .013" 0.33 24" CML 270
5/16" 8 .013" 0.33 30" CML 272
5/16" .013" 0.33 30" CML 272
5/16" 8 .015" 0.38 42" CML 273
5/16" 8 .016" | 0.41 54" CML 274
5/16" 8 .016" | 0.41 72" CML 275
5/16" 8 .017" | 0.43 42" CML 276
5/16" 8 .020" | 0.51 46" CML 277
3/8" 9.5 .011" 0.28 51" CML 279
3/8" 9.5 .013" 0.33 34" CML 280
3/8" 9.5 .014" 0.36 48" CML 281
3/8" 9.5 .014" 0.36 60" CML 282
3/8 9.5 .015" 0.38 53" CML 283
3/8 9.5 .016" 0.41 60" CML 284
3/8" 9.5 .017" 0.43 96" CML 285
3/8" 9.5 .019" 0.48 48" CML 286
7/16" 11 .014" 0.36 72" CML 287
7/16" 11 .018" | 0.46 48" CML 288
7/16" 11 .018" | 0.46 60" CML 289
1/2" 12.7 .015" | 0.38 84" CML 290
1/2" 12.7 .016" | 0.41 66" CML 291
1/2" 12.7 .018" | 0.46 60" CML 292
1/2" 12.7 .018" 0.46 96" CML 293
6/16" 14.3 .015" 0.38 78" CML 294
9/16" 14.3 .018" 0.46 96" CML 295
5/8" 16 .013" 0.33 69" CML 296
5/8 16 .018" 0.46 96" CML 297
11/16 17.5 .015" 0.38 108" CML 298
11/16" 17.5 .018" 0.46 96" CML 299
3/4" 19 .012" 0.31 72" CML 300
3/4" 19 .014" 0.36 108" CML 301
3/4" 19 .016" | 0.41 78" CML 302
3/4" 19 .017" | 0.43 120" CML 303
3/4" 19 .018" | 0.56 96" CML 304
13/16" 20.6 .018" | 0.46 96" CML 305
7/8" 22.2 .018" 0.46 96" CML 306
1" 25.4 .018" 0.46 96" CML 307