Aside from a broken mainspring or physical interference previously by a 'bodger' or someone who simply does not know what he is doing, most clocks only stop working because they need a periodic service or because they've been moved and require setting up correctly again. A longcase or "Grandfather" clock (on which the pendulum swings each way once a second) ticks more than 30 million times a year. A carriage clock ticks close to 150 million times! So it's hardly surprising that any clock over 100 years old may need attention once every few years.
If it runs temperamentally, even a clean-looking clock may still need a proper clean. Don't be misled by a bright and shiny back plate; what really matters is how clean and lubricated are the pivots and their holes - where the arbor (or shaft/axle) of each wheel (or gear/cog) turns in the plates. Dirt and grime accumulate here, attracted and then held by the sticky oil. The build up of dirt gradually increases, thickening the oil and drying it out, causing additional drag which saps the power of the mainsprings or weights. A little too much oil, or the wrong type of oil will often be enough to make a clock run sluggishly and eventually stop. Often, however, it is a chemical reaction between the oil and the brass and steel that causes the old oil to turn to a jelly-like coagulate and this is sometimes manifests itself in the form of a greenish tinge in the pivot holes because over time the oil composition breaks down, especially mineral oil.
Now you'll hear a lot of horror stories about clocks that were left unchecked for years but they're not all just attempts to scare you into paying for your clock to be serviced. If left, insufficiently-lubricated pivot holes will begin to wear oval in shape due to the competing forces of the wheels, and this gradually allows the wheels to drift further and further apart so that eventually only the tips of the brass teeth engage with the steel pinion leaves, and then one day during winding half a dozen teeth are stripped or severely bent. Sorting this out is expensive and results in a clock that has permanently lost some of its value as a collectable antique. Look here for more about how and where to oil a clock.
There's only one reliable way to prevent this and that's by dismantling the movement to separate the front and back plates so that they can be properly cleaned and checked. But before any cleaning is carried out, I normally check the assembled movement for damage and excessive wear before stripping it; cleaning won't do much for a clock with a broken tooth or worn pallets. And if it's really dirty, I might even give it a pre wash to facilitate this important initial inspection and if any serious wear or damage is revealed, I'll tell you first and give you a price.
For speed and efficiency I use four heated ultrasonic cleaning tanks and a robust chemical cleaner for really dirty clocks. One tank is reserved for final rinsing. Through a process of cavitation, the ultrasound transducers create tiny air bubbles in the warm fluid that vibrate and shift the dirt much faster than a long soak. And they can get into tiny holes, cracks and crevices that a brush can't reach. The wheels and other parts are also cleaned in the same way.
Everything then needs to be carefully air-dried (or sometimes in granules of absorbent sawdust) and then handled with gloves to avoid leaving fingerprints; the oils and acids in the skin would gradually tarnish the brass parts leaving unsightly stains after a few months. The parts then need to be checked again as they are reassembled and then lightly oiled in the right places.
If it is important to you that the plates and other parts are brightly polished (say, a carriage clock or a 400-day clock where the movement is under glass and visible), the process of polishing is undertaken before final cleaning so that all trace of the polishing materials are removed in the tank. A finish that suits most longcase clock movements involves brushing French chalk on the cleaned surface - it gives a burnished look, a restrained sheen rather than a reflective mirror-shine, that suits a clock with age. But if the movement is out of sight in a wooden case, the emphasis should be on it being properly cleaned rather than polished at all.
In summary, my 'routine 10-part service' includes:
1. An initial check for correct alignment and proper engagement of teeth and pallets.
2. Dismantling to examine each part including springs for signs of excessive wear and damage.
3. First ultrasonic clean to remove dirt and congealed oil from pivots and pivot holes.
4. Rinsing in second tank and hot air dry.
5. Checking for worn pivots and pivot holes.
6. Checking pallet faces for damage or wear.
7. Checking silk threads, gut lines, suspensions etc. greasing and re-fitting mainsprings.
8. Reassemble loosely for final adjustments to ensure proper operation.
9. Tightening up, and oiling pivots and pallets with the finest synthetic clock oils.
10. Regulation to optimise timekeeping.
Of course, if new parts are needed, like new mainsprings, there will be extra cost but I will ask for your agreement before fitting them. Similarly, if there is any repair needed, like re-bushing worn pivot holes, polishing pivots or re-dressing pallet faces, there will be an additional cost but again I will ask you first.
Some clocks have three winding holes, the most common being vintage, mass-produced, mantel clocks with Westminster chiming on the quarters. They were mainly produced in German factories between the two Wars and might be marked "Foreign" (as Germany wasn't too popular at the time!). Many have cases in the shape of Napoleon's Hat (lovingly referred to as "NapHats" in the trade). Stripping and servicing one of these would typically cost £400, which is more than it's worth, so I offer an alternative to a full strip and clean whereby I remove only some parts (the escapement pallets and strike levers, which all need to be really clean, and the barrels - which contain the carbon steel mainsprings and need to be cleaned and thoroughly dried before greasing and refitting to clean barrels). I then immerse the rest of the movement in an ultrasonic tank of hot, non-ferrous metal chemical cleaner while I remove the three mainsprings from the rinse tank, check, clean and re-grease them. This method of cleaning releases all trace of the congealed oil and dirt etc but won't be quite as effective as a full strip and clean because the pivot holes cannot be pegged out afterwards. After a thorough rinse and dry, I reassemble the movement for testing. It works well for clocks that have little signs of wear but it does not permit any repairs that require separating the plates, like re-bushing or pivot polishing. It does, however, save many of these inexpensive family heirlooms from the scrap heap. If you try this yourself, don't submerse the mainsprings in their barrels because they will very quickly oxidise and then become so corroded that they will have to be replaced.
Often cleaning alone gives a movement a new lease of life so it tends to run more freely and that in turn may mean that it needs regulating again to correct the time-keeping. This is quite easy but for spring-driven clocks it cannot be rushed so if you're in a hurry, I'll explain what is required and leave that to you if you prefer. If you do wish me to regulate it, there's no additional charge but I shall need it for longer and to have the pendulum.
Next, have a look at my clear, easy-to-understand price list.