Seven steps to servicing an antique or vintage clock movement

Why does a mechanical clock movement require servicing? The answer is fairly straight forward.

Keeping your clock in good running condition requires maintaining the movement’s working parts and maintaining the working parts reduces wear. Ideally, most clocks should be serviced every three to five years to maximize longevity and ensure proper functioning.

This article describes the 7 steps that I typically follow when servicing an antique or vintage clock movement. A common American 8-day time and strike, pendulum-driven movement is used as an example.

Seth Thomas 8-day time and strike mantel clock, circa 1875

Step 1 – The clock runs

One of the first things I do when I receive a clock is to determine if it runs. Does it run and strike as it should? Does it complete its full 8-day cycle? I will run the clock and note how many days it will run until it needs to be wound. If it runs less than 8 days there is a power issue which could be any number of things, weak mainsprings, bent arbours and so on.

Step 2 – The clock does not run

If the clock neither runs or strikes when I receive it, I visually inspect the movement for obvious signs, such as broken wheel teeth, bent arbours, broken mainsprings and any resultant collateral damage in addition to missing parts such as a suspension spring or pendulum bob. If all the parts are there, I put it in beat. If it runs I will let it run the full 8-day cycle. If it stops either immediately or soon after, following several attempts, I put it aside for servicing and note the trouble areas.

I make a digital file folder for each clock I service. The file contains many photos taken at different angles and different steps of the process. You will appreciate how valuable a photo is when you are puzzled about where a particular part should go
The front plate is removed on this 8-day movement. All parts excluding the escape wheel

Step 3 – Disassembly and preliminary assessment

After removing the hands, the dial face and taking the movement out of the case I give it a further visual inspection, looking for obvious signs which include the items I noted in step 2. I am also looking for dirt and excess oil to determine how much cleaning needs to be done. I then apply retaining clamps to restrain the power of the mainsprings.

I then disassemble the movement and look at wear areas; pinions, pivot holes, bent arbours, loose connection of plates to pillars, loose clicks and related ratchet issues, presence/absence/condition of helper springs, condition of escape wheel and verge. I also look for tool marks such as scrapes, punch marks around pivot holes, repairs to lantern pinions to determine if the clock has been serviced and how it has been serviced during its lifetime.

Punch mark adjacent to a pivot hole

Step 4 – Parts cleaning

Ultrasonic cleaners are polarizing. It is either love or hate. I won’t go into the reasons why some do not like them but for me, an ultrasonic cleaner is an indispensable tool. If you can afford one, get the best. While there are some decent Chinese machines out there, the American-made L&R ultrasonic cleaner works for me.

Having said that, I will hesitate to put a valuable 200+ year hammered brass movement or lacquered brass into an ultrasonic machine.

Since I am not a fan of ammonia-based cleaners I use a mildly alkaline, biodegradable, odourless, de-greaser concentrate called Polychem Deox 007.

Once disassembled, the parts of the movement can be organized in a container with separate compartments for wheels, levers, springs etc. Once you have done a few movements and become familiar with the parts and where they go, everything goes in one tray.

As for open-loop mainsprings I make it a practice to detach the mainspring from the wheel for cleaning. Sometimes they are very stubborn and rather than risk damage I put both the wheel and the mainspring in the ultrasonic cleaner separately.

After the mainspring/wheels are cleaned I inspect the solution to determine whether to continue using it or toss it. If it not too dirty (and I will reuse the cleaner several times) I put the remainder of the parts into the ultrasonic. Wiping off excess oil and grease before placing the parts into the ultrasonic is highly recommended.

Ultrasonic cleaner by L&R
Ultrasonic cleaner by L&R

Drying the parts is vitally important. Do not let the parts sit with water on them for any length of time. Rust will form very quickly.

A good day to dry parts is when your partner is baking. Once they are finished, the residual heat from the oven is great for drying clock parts. Otherwise, a hairdryer is your best friend.

Step 4 – Polishing pivots

Polishing pivots is the next step. If the pivots are in good shape a few passes with an emery board are all that is needed. If the pivots are pitted, the wear must be mitigated with more aggressive cleaning and polishing. At worst a pivot may need to be replaced, rare, but it happens. If there isn’t much loading on the pivot you may get away with turning the pivot to a uniform diameter, and polishing it but such work is challenging and requires a metal lathe.

Polishing a pivot

A small metal lathe is a great advantage for clock repair though a cordless hand drill will suffice for some pivot work.

A clock hobby can be expensive. It took me about 6 years to purchase the equipment I required taking an as needed approach. I caution the reader that it is always tempting to buy cheap. My first ultrasonic was a bargain basement jewelry cleaner and it could not clean anything. Spending a few dollars more for a better one is already paying dividends

Every pivot is cleaned and wiped clean with a soft cloth. Next is bushing (if required).

Step 5 – Bushing, broaching and pegging pivot holes

From time to time I come across a movement that does not require bushings but that is the exception rather than the rule. I am also not a fan of bushing everything. If the pivot hole is passable and the pivot itself is in good condition, plus there is good gear meshing and end shake I leave them alone until the next inspection.

I am also not a fan of hand bushing. It is very challenging to get everything true using strictly hand methods and I admire those who bush by hand but for me, a bushing machine is a necessity for serious clock repair. There are two systems, KWM and Bergeon. There are fans of both systems but in truth they are equals. Each system comes with reamers, stakes, driving punches and so on.

Here is an example of pivot hole wear.

Close-up of bushing wear
Close-up of bushing wear on the left side, with Sharpie dot

I approach bushing in three phases.

  1. I assemble the time side gears and look for pivot hole wear by observing the lateral movement of the pivots that tell me if there is wear in the pivot hole. Some even describe the pivot as “dancing” around the pivot hole. Using the top or bottom plate, place the pivot in its hole and if there is more than 5° of tilt in all directions (although this depends on the thickness of the plate), the hole is worn. A dot with a fine point Sharpie beside the hole tells me what holes require bushing.
  2. I then proceed with the strike side gears and mark what bushings, if any, are required.
  3. Last is the motion works.

Once I have determined what holes need work I proceed to bush using my Bergeon bushing machine. Once the bush hole is made it is time to clean the hole from chips and burs that came about while making the hole. This is done with the use of the chamfering cutter, this tool is spun once or twice on each side of the hole and it makes for a clean edge. The bushes are then pushed into place.

If the hole is smaller than the pivot diameter it needs to be broached. I use the appropriate size cutting broach followed by a smoothing broach. The smoothing broach is used to harden the bushing hole through a process called burnishing.

All the pivot holes are pegged until there is no residue left on the toothpicks. You will use plenty of toothpicks.

Centering prior to drilling
Centring prior to drilling

Step 6 – Making necessary repairs

Other repairs might include but are not limited to re-pivoting, straightening or replacing wheel teeth, sourcing parts from donor movements or an online supplier, making parts (for example, a new lever), replacing helper springs and wires in lantern pinions and new suspension springs, rods and verges.

Step 7 – Reassembly, testing and adjustment

Once the bushing work is completed it is on the next step, reassembly, testing and adjustment. For re-assembly on a typical 8-day movement once all the gears and levers are in place on the bottom or rear plate I put the top plate on, secure the pillars nearest the mainsprings with screws/wires/pins loosely, at first. Once the plate is stable I work on the time side next by loosely securing it to the top pillar with a screw/wire/pin.

Then it is on to the strike side. It is difficult and frustrating to move the gears and levers in place without a pivot locator and this is precisely where you need one.

Once the movement is re-assembled it is placed on a test stand, placed in beat and regulated/adjusted if necessary. Testing can take up to a month on the stand before the movement returns to its case.

A Gilbert time-only movement on a test stand

Conclusion

Servicing an antique or vintage clock extends its life immeasurably. The 7 steps I take when servicing a clock movement is not a definitive guide, some of the steps require further explanation and there are likely some procedures that some would do differently.


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