Expert: Martin Meyer - 10/21/2009

Question
I have a carriage clock which was bought new in the UK about 3 years ago. The maker is the London Clock Company. I have wound it using the supplied key once a week without problem until this week when something snapped and the key now simply turns uselessly. There is a cog at the back of the clock which has a small 'arm' and a spring. I can supply a picture if requested. I hope you can help. Thank you.

Answer
Hi Alison,

Your clock's mainspring either broke or its end slipped off the stud which holds it. You can't see the mainspring because it is in the brass barrel whose shaft becomes square and is where you wind the clock.

I'm not sure what you mean by the "cog", but the only part I can think of that is related to winding the mainspring is the ratchet assembly which keeps the mainspring wound. This consists of a saw-toothed ratchet wheel on the mainspring shaft, the "click" (a pawl) which slips into the teeth of the ratchet wheel, and the clickspring, a bent wire which presses on the click and keeps it in the notches of the ratchet wheel. If the winding key turns freely but doesn't wind the clock, the mainspring is your problem; as long as the winding key will only turn in one direction, the ratchet assembly is okay.

Replacing the mainspring is a major repair. On all but a few clocks, it is necessary to take apart the two main plates which hold all the gears and parts in the movement, in order to remove the mainspring barrel, open it and install a new mainspring. This is a labor-intensive, and thus expensive, repair because of the difficulty of replacing all the gears, some of which have to be indexed very precisely relative to others.

Your clock may no longer be under warranty, but I would suggest contacting the manufacturer about this problem first. Three years, although probably past warranty, is still far too soon for a mainspring to break, unless the clock has been abused. In this case, "abuse" would most likely consist of winding the mainspring extremely hard, that is, with nearly all your strength, which I suspect is unlikely. The London Clock Company is now LC Designs.  http://www.clockmasteronline.com