Mainspring barrel tooth damage – how does that happen?

Something causes tooth damage. But what?

The example is a Fleet time and strike mantel clock from the 1930s. Fleet Time Company of Montreal, a company that was operating four short years, sourced movements from Germany prior to the Second World War. It was a very common mantel clock sold through department stores across Canada.

I like the step side design and the general simplicity of the clock.

Fleet Time case
Fleet Time case, refinished

The case was in need of refreshing but the movement looked to be in reasonably good condition and required a good cleaning and I was expecting some wear.

The movement was completely serviced with several new bushings installed. The mainsprings were removed, cleaned, and returned to their barrels.

Fleet time movement
Fleet time movement

In this movement, the mainsprings can be removed without disassembling the movement, handy for such things as replacing a broken mainspring assuming, of course that nothing else has been damaged.

During the testing phase, the mainsprings were partially wound. The intent was to see if the clock would run well. Once satisfied that the movement was running as it should I returned it to its case.

I wound the strike side fully and then wound the time side. Just as I was feeling resistance, CLUNK, the arbour turned freely. If it was a broken click or broken mainspring, either one could easily be replaced.

It has nothing to do with the force of winding a movement. Having a mainspring go bad with winding force from a key is rare, in my view.

But mainspring barrel teeth do not simply fall off.

Fleet time barrel
Fleet time barrel

At times it is a mainspring but sometimes something far worse occurs.

It is not uncommon to find secondary damage to the movement, secondary or collateral damage due to the extreme shock that broke or bent the teeth and teeth cannot be straightened.

The main problem area beyond the barrel itself will be the second wheel and possibly the third wheel arbors, leaf pinions and pivots and/or damaged or missing teeth on the second and third wheels and bent or broken pinions.

Fleet second time wheel
Fleet second wheel, a bent leaf cannot be unbent

Is it fixable? Yes, but weighed against the value of the clock, it is just not worth it. It is much more cost effective to harvest parts from another movement.

Given the right equipment, it can be repaired. Once repaired a mainspring must be sourced and although the barrels may be identical, the mainsprings will likely be different.

The solution is locate a donor movement. In the meantime the clock has been put aside.

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