Why is my clock striking 12 continuously?

[tyl604]

Very odd. My tall case clock has always run perfectly. Still keeps great time. But for the last few days it strikes twelve times on every hour.

Anyone know what might be stuck? And how I can get it unstuck? Old clock from about 1850 as I remember.

Would picture of the clockworks be helpful?

[INSIDIOUS]

Pull out that mouse that got jammed in the gears

[barry12345]

Visual observation of the movement when working might reveal something. It should be repairable. Even just something needing lubrication.

Did you get the lifetime warranty when you purchased it new?

[tyl604]

Will have to ask my mother-in-law.

[Mxfrank]

There are two common mechanisms used for striking clocks.

The first is a counting wheel, which is a wheel which revolves once every 12 or 24 hours. Along the edge, there are notches. As you go around the wheel, the number of degrees between the notches increases. A counting arm will ride around the the outer circumference of the wheel, and allow the clock to strike until it falls into a notch and locks. It's very difficult to get this sort of mechanism to fail in the manner you describe. The usual failure mode is for it to ring until it runs out.

The second type of mechanism is the rack and snail. When it's time to ring, a rack drops onto a spiral cam driven off the canon pinion. A gathering pawl then reloads the rack one tooth at a time until it gets back to it's resting position. In order for the clock to ring 12 times every hour, the rack would need to miss the snail and fall onto some sort of backstop. Which suggests that the snail has become detached, or if that it's gear driven and the gear has stripped. If you can remove the face and photograph the mechanism, I may be able to give you a better idea.

Although this isn't the most complicated repair, it's not something you just go do unless you have experience with clockwork mechanisms and proper tools. Not only are the parts delicate, but the gears have to be oriented properly for it to work. If you don't know a local clock repair shop, try the boards at Welcome to the NAWCC!.

[tyl604]

M - great info. Just what I needed. Will look into it and post some pics.

Much appreciated.

[INSIDIOUS]

Be very careful - do not ask for whom the clock tolls ...

[tyl604]

Mxfrank - OK; here are some pics. Do you see anything?

[Mxfrank]

Nice clock. I'm going to guess British, early to mid 19th century.

You would need to remove the face to get a clear picture of the strike mechanism. From what I can see, you have some loose string caught in the strike train. You can clean this out with a pair of tweezers. I don't think it's causing the problem, but it's not good to have loose stuff in the movement. Also some cobwebs which you should blow out with a pressure duster. The movement appears to be very dry and could use a teardown and fresh oil. I really recommend a professional overhaul. If you want to try this yourself, you would do well to join a local chapter of NAWCC and find someone willing to work with you. You really need to get someone to nurse you through the apprentice stage. I'll talk you through this as best I can if you really want to do this online. Before you do any work, it's best to remove the pendulum and weights.

I'll tell you how to remove the face, but if you are at all uncomfortable, just stop. And remember, anything you break will have to be made from scratch. It's a good idea to cut a piece of cardboard to protect the face as you work. First remove the hands. The seconds hand should just pull straight out. The hour and minute are most likely pinned. The pin may be either straight or tapered. If it's a taper pin, you want to grab the fat side of the taper and pull straight with a pair of pliers. There will be a washer under the pin, and then the hour hand will immediately come loose. The minute hand is friction fit to the cannon and should pull out without much drama. To remove the face, there will be four pins that mount the face to the front plate (don't confuse them with the pins that hold the plates together). When all four pins are out, the face will be free. See the annotated photo below.

[tyl604]

Yes, I have had the face off several times over the past forty years. Will do it later and post some pics.

Appreciate your help.

[Mxfrank]

What I expect you will find is something like the attached photo. When the clock reaches the hour, a follower falls onto the snail and allows the rack to drop a controlled distance. The rack is then gathered up one tooth per revolution of the strike mechanism. The snail may be loose on the pinion, which would require it to be staked, or the follower is out of position for some reason. You can work the mechanism by installing the hands without the face. Advance the minute hand until the strike sequence begins, and observe what happens.

[tyl604]

Will be able to look at it later today; obligations now.

Thanks.

I do kinda remember seeing the snail mechanism in the clock from years back. At that time it would only strike ten times at 11 and again at 12; otherwise it struck the right number of times.

Has struck like that for years (1-2-3-4-5-6-7-8-9-10-10-10-1-2-3-etc) until mysteriously this week it started striking twelve times on each hour. Is an interesting challenge and I like being educated anew.

[Aquaticedge]

Whens the last time you serviced it? could need a good cleaning and oiling, I have 2 down right now for just that, I'd love to see the whole clock, I'm starting a bit of a collection....

[Mxfrank]

Here's an old diagram explaining the mechanism. Each clock is different, but the conceptual mechanics will be the same.

What you're looking for is some sort of problem between the rack and snail. It could be that the snail is loose on the canon pinion. For that vintage of clock, it's probably staked in place and you don't want to attempt that repair without practice. The other possibility is that the cam follower or spring is broken, fouled, or sticky. You fix a clock with your eyes before you fix it with your hands.

[TX76513]

This forum never ceases to amaze me with the depth of knowledge of the membership.