Forestville mantel clock servicing – not fun when things go wrong! Part II

The face of Forestville bim-bam clock

Back in October (2020), I wrote about the challenges of working on this mantel clock by Forestville.

Recap so far

It is a nondescript Art Deco-style German mantel clock made in the 1960s sold under the Forestville name, a Toronto-based company that assembled clocks up to the 1970s.

The rack and snail movement is relatively simple to work on with all the adjustments, save for the stop wheel, on the outside of the plates. The mainspring barrels can be removed separately for servicing, typical of movements of the period.

An arrow pointing to the centre wheel

The hairspring escapement is something I did not attempt to clean. They can be finicky to work on and if the movement has been running beforehand, like this one, there is no pressing need to mess with it. Three screws detach it from the movement.

The bane of clockmakers – the broken pivot

When working with German and French movements particularly one must always be very careful of the small pivots. Normally when I work on this type of clock I am very aware of how easy it is to bend or break the tiny pivots and this clock was no exception. After taking apart the movement and reinstalling the gears to determine bushing wear I noticed the front plate center wheel pivot had come off.

Thinking I was careful guiding each pivot in place with a pivot locator I either applied too much pressure closing the plates or it was hanging on like a tread. Regardless, it broke. Compared to a pair of tweezers it is very small.

Broken pivot compared to a pair of tweezers

My experience with pivot repair is limited. I don’t come across broken pivots very often. Compared to an American clock that has much larger pivots these are tiny, perhaps 0.5mm or so. Although I have bushings that fit I do not have pivot wire that size and had to make do with a piece from my assortment of 0.85mm to 1.10mm wire. Not pretty but functional.

First, using a centring bit followed by a high-speed bit on my Taig metal lathe, I drilled 5mm into the shaft, enough to securely anchor the pivot wire. Once the wire was inserted, I applied high-strength Permatex Threadlocker Red to secure the wire in place.

A centring bit is essential when drilling a starting hole in an arbour.

After the 24 hour curing period for the adhesive, I installed a bushing in the front plate and put the gears back together to check the action of the new pivot. It is working okay. I will reserve judgment on the repair until the other bushings are installed.

There is more wear on the time side that at least 3 new bushings are required, two on the front plate and one on the back.

Out of an abundance of caution, I installed an additional 2 bushings. In total are T2, T3, T4, rear plate, and T4, T5, front plate. All bushings are on the time side which tells me that the strike side did not see much action, typical for many mechanical clocks since some folks find the noise of the strike bothersome.

2 new bushings on the front plate, new pivot in the centre of the photo (untrimmed)
3 new bushings on the rear plate using a Bergeon Bushing Machine

Servicing the mainspring barrels was more frustrating than I anticipated. Both mainsprings refused to catch on their hooks when I attempted to install them back into their barrels. The mainspring opening must be precisely on center to catch. Lesson learned; after a few tries, I successfully got them hooked back into the barrels.

Re-assembly

The new pivot was trimmed to fit and given a final polish prior to installation. Now to put it all together and see if the work has paid off.

I was especially careful putting everything back together and very mindful of how easy it is to snap off one of the delicate pivots. All went well. On the test stand, I ran the strike side through its sequence; it is going into warning and striking on the half-hour as it should. Now for the time side.

Repairing a broken pivot. Left on the lathe overnight to cure the adhesive and keep the pivot straight.

At first, the escape wheel would stop after a minute or so but after oiling the pivots including those on the hairspring (minus the jewelled ones, of course) it runs well.

Testing the Forestville movement on a non-standard stand

I will continue with the test of the movement but so far, after two 8-day running cycles, things are looking very good. The next step is to re-install the strike hammers and other moving parts and return the movement to its case.


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