My “new” antique clock stopped running today. This doesn’t surprise me a lot- it has travelled half way around the world, and it is pretty old, so it being a bit out of sorts is somewhat expected. But I had some learning to do in order to figure out what was going on, and to see if it could be “fixed” without major challenges. I’ve collected some of what I found here for future reference.
There are two basic types of regulating mechanisms in mechanical clocks: a pendulum or a balance wheel. Both serve the same purpose: controlling the output of mechanical energy from a spring or weight drive using simple physics (i.e.: gravity). Without this regulation, the spring would spin down and the clock wouldn’t measure time accurately.
Balance wheels are more “modern”, and so of course my older clock has a pendulum. Pendulums  are neat in that, as a result of the mechanisms they inhabit within a clock, produce the wonderful tic-tock (or tic-tic) sound we think of as measuring time. Interestingly, that sound should be precisely even, and if it isn’t, the clock is said to be “out of beat”. Being out of beat is basically a matter of balance: the pendulum is swinging more to one side then the other, or worse yet isn’t swinging straight side to side, but also front to back. It loses energy on each swing, and in most cases will stop swinging entirely in a short while- which of course stops the whole clock. The spring is still wound, so there is energy there waiting to be used, but it is the pendulum that puts that energy to work telling time.
Some pendulum regulated clocks have “auto-adjusting” mechanisms to rebalance themselves, but once again this is generally a feature of newer clocks. But as soon as you realize that being out of beat is mostly a matter of balance, you can start making careful experiments to correct the level of your clock. Without making any changes the mechanism, this can be done simply by lifting one corner or side of the clock a fraction of an inch while the pendulum is swinging. That beat of that wonderful “tic-tock” sound will change and either become more “balanced”, or more erratic. I can attest to the fact that this takes some practice, and the smart thing would be to have a nice collection of finely sized wooden shims to prop the clock corners up as you experiment.
On my clock a shift of about 1 mm on one side was enough to improve the balance: it isn’t perfect, but if the clock runs for more than eight hours I’ll know it is a step in the right direction. If you have to shim up a side so much that the clock looks out of kilter, then the adjustment needs to be made mechanically: that is, the internal balance point needs to be corrected. It is important to note that simply using a spirit level won’t help you here unless the clock is brand new and is already perfectly adjusted: the out of beat condition usually occurs in older clocks or clocks that have been moved recently, and generally “level” isn’t what they need to get back in trim.
I referred to several  different  sources  to get the basic information I’m relaying here. Some of these sources refer to specific ways to correct the beat that may only apply to certain types of clocks (e.g.: those with “auto correcting” balance), but be careful: these may involve moving the pendulum / pendulum crutch to the extremes of their motion and, if the clock doesn’t have auto adjustment features, you can cause damage. Generally, though, if you are gentle you won’t likely be inflicting permanent harm.
I’ve put some bits of cardboard under two of the legs of my clock for now, and keep listening to its tic-tic sounds: if it is still running a day or two from now, I’ll look into a more permanent solution.