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Hermle (pronounced "Herm-lee") was founded by Franz Hermle in Württemberg in Germany in 1922. Their clock movements are distinctive and easily identifiable by the rows and columns of light counterpunch marks on the brass plates. Most have the name Hermle on them but occasionally you'll see the initials FHS (for Franz Hermle and Son) instead. I've even seen other styles, too, but they all have the counterpunch marks.

Hermle are now the biggest manufacturer of clock movements in the world, making thousands of different versions for different purposes. The two most common in the Westminster chime versions with a pendulum are the 340 series driven by weights for large wall and floor-standing clocks, and the 341 series driven by springs) for mantle clocks and smaller wall clocks (see opposite, top). Within each range they have two very common alternatives, the 020 with its long centre arbor (33.2mm), which it suitable for deeper dials (or front mounting where it has to pass through the wooden case as well as the dial), and the 021 with a shorter centre arbor (27.6mm), making it suitable for shallow dials (or rear mounting where it only has to pass through the dial). They are not interchangeable.

Hermle movements in smaller two-train clocks that have no pendulum and strike the hours and half hours on a bell (but no quarter-chiming) often have a 130-070 floating balance movement with circular plates.

Dating Hermle movements is easy if you look at the back plate (see the table below right). Up until 1987, they simply added the last two numbers of the year of make - so 77 indicates 1977. But rumour has it that retailers complained about the system because their customers could quickly spot old stock lines. So in 1988 Hermle adopted a letter code starting with A, so the letter 'O' (in the second illustration opposite) denotes 2002, and so on. You should note, however, that it's not completely reliable; in 2012, I bought a new movement with the date letter denoting 2001 so I suspect Hermle are using up old stock to clear it. Nothing wrong with that as they're unused.

Being cost-concious, Hermle's brass plates are thinner than those found in some older clocks and this sometimes leads to pivot holes wearing more quickly, especially in clocks that are not oiled every three years. Worn pivot holes can be re-bushed but some of the pivot holes are so close to the edge of the plates that re-bushing is not safe. Also, mainsprings seem to be less durable so a frequent complaint is that a ten year old Hermle clock will only run for four of five days instead of the usual eight, and that the strike and chime sound sluggish a few days after winding or stop altogether.

Fortunately, however, because of the efficiencies of large scale production, it often costs little more to replace a Hermle movement than to strip, clean, rebush, reassemble and oil the existing one. And if yours has mainsprings that need changing, it will actually be cheaper! The springs themselves add around £40 each to the cost of a service (£150). So a new three train movement will typically cost £200 to supply and fit, whereas the cost of servicing your existing one will be £270. Small striking mantle clocks are also cheaper to replace, typically £160 (as opposed to £180 for a service and two new mainsprings). The existing dial, hands and gongs are all re-used so the clock still looks and sounds the same. And of course it's quicker so you can have your clock back in a fortnight or less.

You could save a bit by buying a replacement movement direct from one of the material houses that supply the trade if they deal with the public but it's not always straightforward. Tthe model you have may have changed and even though the model code is the same, it could now incorporate auto night silence instead of manual chime / no-chime, and that could be incompatible with a moondial feature if your clock has one. You will also need to transfer the old dial, hands and gong hammers and set them up to activate correctly so it's not just a five minute swap.

If these costs exceed what you can afford, there is a cheaper alternative, which is to remove, soak, wash, rinse and dry the movement without first dismantling it. You cannot immerse the mainsprings in the cleaning solution because they will oxidise (rust) and the clock will quickly stop. But like most German movements, the Hermle design allows the mainspring barrels to be removed without separating the clock plates. This is helpful because stripping and rebuilding a clock is time-consuming and therefore expensive, so it can be avoided. At just £50-£70, it all adds up to 50% less than a fully stripped service, though the guarantee is shorter (3 months) because even in an ultrasonic tank with the best cleaning fluids, a fully assembled clean cannot remove every trace of dirt. And of course it won't help if the mainsprings are worn out or if any pivot holes are worn because re-bushing requires dismantling.

In case you're wondering, a three train version is more expensive than a two train even for a fully assembled clean because the underslung chime assembly has to be removed to get the Going barrel out and that means you're faced with the setting up of the chime sequence after you put it back again.

Incidentally, for any repairers reading this, I've found that the simplest way to reset the chime on the underslung unit is first to prise off the circlip holding the lower of the two four-spoke wheels of the chiming train on the outside of the backplate (see third photo opposite); then slide the wheel off a little so that it disengages from the two smaller wheels above and below it. Next, turn the loose bottom wheel until you see a run of four hammer movements in sequential order (1, 2, 3, 4) and stop - the chime train has now run the 'quarter past' position. Now run the going train by turning the centre arbor until it strikes the hour (any hour), and then rotate it through another another 90 degrees until one more chime activation, and stop. Finally, without moving either of the two smaller wheels, refit the four-spoke wheel to re-engage the chiming train again and refit its circlip.

Overall, Hermle movements aren't the easiest to work on but they're decently made and will last the owner's lifetime if checked and oiled periodically. After all, Hermle would not be the largest producer of mechanical clock movements in the world if their products weren't good.

For more, check out the Hermle website.

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2 and 3 train movements

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Dating your Hermle clock

On the brass backplate of your Hermle clock movement you will find either two numbers (pre-1988) or a capital letter (post 1988) which denote the year of make: