I had just completed servicing this German Mauthe time and strike wall clock and everything seemed to be going well. It was keeping good time,striking on the half hour as it should and maintaining a consistent an 8-day cycle.
During my regular Saturday clock winding ritual, I decided to begin with this clock. I inserted the key into the strike side arbour, began to turn the arbour and “bang” went the mainspring. The winding key almost took my thumb off.
Ignoring the excruciating pain I just had to investigate the problem. I took the movement out of the case and took the dial off. Of course, I feared the worst. A sound like that is never good. The barrel seemed undamaged, the teeth were intact, no bent arbours and there did not appear to be any collateral breakage.
Aha!, there it is, a loose click spring. The click released when there was not enough tension on the click to hold it firmly to the ratchet wheel.
My fault entirely. When I dis-assembled the movement I bent the click springs out of the way and did not recheck the spring’s tension. When I re-assembled the movement the click on the strike side was evidently loose but it looked tight enough. I wondered why the strike side ratchet sounded “tinny” but I thought nothing of it. Now I know.
I increased the tension of the click spring. To be on the safe side I checked and tightened the time side one as well. Both sides now have that reassuring click-click sound. As you can see in the above photo It is not the best click spring design.
A reminder to anyone working on clocks that potential (or stored) energy in the form of powerful mainsprings can be dangerous. All is well, lesson learned. But my poor thumb!