Disassembling a Junghans Joker Musical Alarm Movement: Hairspring Removal and Stuck Taper Pin Extraction

The Junghans Joker musical alarm movement — and similar Junghans and Mauthe alarm clock movements from the mid-twentieth century — presents specific disassembly challenges that differ from typical American or German mantel clock movements: a lever escapement with a delicate hairspring that must be removed safely before any plate separation is attempted, taper pins that have undergone metallurgical galling after decades of contact between steel pin and steel arbor, and in some versions an unusually long taper pin whose purpose is not immediately obvious from inspection. Each of these challenges has a solution, but the correct approach for each is different from what works on more common clock movements, and attempting the wrong method can result in a broken taper pin stub that is harder to remove than the original pin, or a deformed hairspring that cannot be corrected without specialist watch repair equipment.

This guide covers the complete disassembly sequence for the Junghans Joker musical alarm movement — how to safely remove the balance wheel and hairspring assembly before any other disassembly, marking the hairspring position for correct reassembly, why Junghans taper pins gall against steel arbors and what the correct extraction approach is when the pins have already broken flush, the dental burr grinding method for removing broken taper pin stubs without damaging surrounding components, the correct orientation of the alarm activation taper pin relative to the arbor collar, the function of the long taper pin on the alarm mainspring post and why it is designed to prevent spring coning into the adjacent wheel, and how to source replacement mainsprings when the originals cannot be removed without cutting.

Removing the Balance Wheel and Hairspring First

Why the Hairspring Must Come Out Before Plate Separation

The lever escapement used in the Junghans Joker and similar musical alarm movements positions the balance wheel and its hairspring between the plates in a location that, if left in place during plate separation, exposes the hairspring to contact with the plate edges, other components, and the technician's tools as the plates are moved apart. The hairspring is a coiled strip of steel thinner and more delicate than any other component in the movement — it can be permanently deformed by contact with anything during plate separation, and a deformed hairspring changes the balance wheel's oscillation period, producing a movement that keeps incorrect time and cannot be corrected by simple rate adjustment. Removing the balance wheel assembly as the very first disassembly step — before touching any plate screws or other components — eliminates the risk of hairspring damage during all subsequent disassembly work.

The balance wheel on these movements is held in place by a taper pin that passes through the arbor of the balance wheel assembly. Before attempting to remove this pin, mark the position of the hairspring's inner coil where it contacts the taper pin with a fine-tipped permanent marker — this mark records the correct angular position for reassembly, saving significant time during the reassembly phase when finding the correct adjustment position can otherwise require extended trial-and-error testing. With the mark made, remove the taper pin using a taper pin remover tool or a shaped punch, and the balance wheel assembly will be free to lift clear of the movement without any further disassembly required. Handle the assembly by the balance wheel rim or the outer edge of the balance cock rather than by any part of the hairspring, and set it aside in a protected location where nothing can contact the hairspring during the remainder of the work.

Taper Pin Orientation for the Balance Wheel

Taper pins taper from a larger diameter at one end to a smaller diameter at the other, and they must be driven out from the correct direction — pushing on the small end drives the pin deeper into the hole, while pushing on the large end drives it out. For the alarm activation taper pin on the Junghans Joker, the large end of the pin faces toward the notch on the arbor rather than away from it, which can be counterintuitive on first examination. The raised collar near the notch provides a seat for the large end of the pin and is part of the retention geometry — the large end rests against the collar and cannot be driven through it, ensuring the pin can only be removed from the small-end direction. Identifying the correct driving direction before applying any force prevents the common mistake of driving the pin deeper by pushing on the wrong end, which compresses the pin more tightly into the hole and increases the galling contact that makes it harder to remove.

Understanding Galling: Why Steel-on-Steel Taper Pins Seize

What Galling Is and Why It Occurs

Galling is a form of adhesive wear that occurs when two metal surfaces in close contact under pressure undergo localized welding at their contact points. When steel slides against steel under the contact pressure of a taper pin in a steel arbor hole, the natural oxide layer that normally lubricates the contact is broken down at microscopic high-spots where the actual metal contact occurs, and the clean metal surfaces at these spots weld together momentarily. As the pin is driven or pulled, these micro-welds shear off and re-form at new positions, progressively transferring material between the pin and the hole wall. Over decades of the pin remaining stationary in the hole, the micro-welded contacts consolidate into a cold-weld bond that is effectively indistinguishable from a continuous material connection across the contact surface. Removing such a galled pin requires breaking all these micro-welds simultaneously, which requires far more force than removing a non-galled pin of the same size.

The use of dissimilar metals prevents galling — a brass pin in a steel arbor hole, or a steel pin in a brass arbor, does not form the same degree of micro-welding because the different crystal structures and surface properties of the dissimilar metals reduce the tendency for material transfer at the contact points. This is why quality clock movements traditionally used brass taper pins in steel arbors. When a steel taper pin is used in a steel arbor — whether from original design where the load on the pin required steel's greater strength, or from a repair where the correct brass pin was not available — galling is eventually inevitable, and the pin that was correctly installed with moderate force may eventually require destructive methods to extract.

Why WD-40 Has Limited Effect on Galled Pins

WD-40 and similar penetrating lubricants are useful for loosening pins held by corrosion — rust that has expanded and mechanically locked the pin in its hole. However, galling is not corrosion-based mechanical locking but rather a metallurgical bond between the contacting metal surfaces, and penetrating lubricants cannot dissolve or break down this bond. Applying WD-40 to a galled taper pin and waiting does not significantly reduce the force needed to extract it. The only approaches that work for a truly galled taper pin are applying enough force to shear the galled bonds — which may require more force than can be applied without risking plate damage — or removing the pin material by grinding rather than by pulling or pressing.

Extracting Broken Taper Pins: The Dental Burr Method

When Pulling and Tapping Have Failed

When a taper pin has broken off with both ends flush or nearly flush with the arbor surface — usually because an extraction attempt applied pulling force that exceeded the pin's tensile strength before the galling bond released — the remaining stub cannot be removed by any tool that must grip or press on the pin's end. The remaining stub material must be removed by grinding or cutting rather than by mechanical extraction. The dental burr method uses a small burr mounted in a Dremel or similar rotary tool to carefully grind away the protruding pin material flush with the surrounding arbor, allowing the components to be disassembled and the remaining stub hole to be cleaned out after the arbor is freed from the plate.

Select a dental burr whose diameter is small enough to work in the confined space around the taper pin stub without contacting the surrounding clock components. Work at low rotary tool speed to maintain control and minimize the risk of the burr jumping off the hard pin surface and contacting an adjacent wheel or plate. The goal is to remove just enough material from the protruding pin stub to allow the wheel or component that the pin was securing to be freed from the arbor — not to drill or grind out the entire pin from inside the arbor hole, which can be done after the arbor is removed from the movement. Once the protruding stub has been reduced to flush with the arbor surface on the side where it was interfering with component removal, test whether the component can now be freed. If it can, proceed with disassembly and address the remaining pin stub in the arbor hole after the arbor is free.

Drilling Out the Stub After Freeing the Arbor

After the arbor has been removed from the movement, the remaining taper pin stub inside the arbor hole can be drilled out with a drill bit slightly smaller than the pin diameter, removing the core of the stub while leaving a thin wall of pin material against the hole walls. This remaining thin wall can then be collapsed inward with a fine pick or scribe and extracted as fragments, or the drill can be progressively stepped up in size until the remaining material is removed. Drill at low speed with a sharp bit and apply light pressure — the goal is controlled material removal, not aggressive drilling that could break the bit or damage the arbor. After drilling, clean the hole thoroughly with a peg wood stick and inspect for any remaining pin fragments that could cause interference with the replacement pin to be installed during reassembly.

The Long Taper Pin on the Alarm Mainspring Post

What the Long Pin Actually Does

The unusually long taper pin found on the alarm mainspring post in some Junghans Joker movements — a pin that runs partway up the movement rather than being a short cross-pin through the arbor — has a specific function related to the geometry of the alarm spring and its adjacent wheel train. In the Junghans Joker, the alarm mainspring barrel is positioned such that a portion of the second alarm wheel sits between the mainspring and the first alarm wheel, creating a configuration where a freely expanding mainspring coil could work its way upward into contact with the second wheel as the spring unwinds through its range. The long pin on the mainspring post extends above the mainspring to act as a physical barrier that prevents the spring's inner coils from coning upward into the space where the second wheel is located.

This pin arrangement is constrained laterally by internal pins and the semi-circular plate attachment that confines the mainspring as it unwinds. The long external pin prevents the mainspring from migrating upward into the adjacent wheel train as the spring reaches the end of its travel. Understanding this function is important because removing or shortening the long pin in a misguided simplification of the assembly would remove the spring's vertical constraint and could allow it to contact and damage the adjacent wheel during operation. When this pin is found galled and cannot be removed without breaking, the safest approach may be to leave it in place and replace the mainspring by cutting the old spring out and reforming the hook on a new open-loop spring of the correct dimensions.

Mainspring Replacement When the Posts Cannot Be Cleared

For movements where the mainspring retaining taper pins are galled beyond safe removal — and where the mainspring access requires clearing the pin — an alternative approach is to cut the old mainspring loop and remove the spring from around the still-installed pin, then replace with an open-loop mainspring that can be installed without threading the spring over the pin. An open-loop mainspring of the correct width and thickness but slightly greater length than the original can be cut to the correct length and the inner hook reformed to fit the movement's barrel arbor hook, without requiring that the long retaining pin be removed at any point in the process. The replacement spring holds the pin in place after installation just as the original did, and the pin's coning-prevention function is preserved without the need to remove and reinstall it.

Reforming the inner hook on a mainspring end that has been cut from an open-loop coil requires annealing the cut end — heating it to a dull red and allowing it to cool naturally — to soften the steel enough to be bent without cracking. Once annealed, the softened end can be bent with pliers to form the hook geometry needed to engage the barrel arbor hook, shaped to match the original spring's inner hook geometry using the removed original as a reference. The annealed section will be softer than the rest of the spring, which is acceptable since the inner hook is not a load-bearing section in the same way as the spring body — the inner hook simply provides the attachment point while the spring body carries the elastic load.

Sourcing Replacement Mainsprings for Junghans Alarm Movements

Measuring and Ordering

Replacement mainsprings for Junghans musical alarm movements require measurement of three dimensions: the width of the spring strip (measured across the flat face of the spring), the thickness of the spring strip (measured across its edge), and the total length of the spring from inner hook to outer tip. These dimensions in millimeters are the specification needed to order a replacement from a clock supply house. The Junghans Joker alarm mainspring is approximately 7.5mm wide by 0.46mm thick by 1190mm long in the time train version, and similar for the alarm side — close enough to a 7.5mm by 0.42mm by 1420mm open-loop spring from major suppliers to serve as a replacement after length adjustment by cutting.

When the original spring cannot be removed intact for measurement — because cutting it out was required — measure from the movement's barrel dimensions using the theoretical formula: spring length equals pi times the difference of the squares of the inner and outer barrel radii divided by twice the spring thickness. This gives the theoretical correct spring length for a barrel of given dimensions and spring thickness, providing a starting point for ordering when the original cannot be measured directly. In practice, clocks are tolerant of some variation in spring length — a spring somewhat longer than theoretical will wind more tightly at full wind and a spring somewhat shorter will not fill the barrel as completely, but both will run the movement satisfactorily within a reasonable range around the theoretical ideal.

Reassembly Considerations

Reinstalling the Hairspring

When reinstalling the balance wheel assembly after servicing, the mark made on the hairspring before removal identifies the correct angular position for the inner coil to be positioned relative to the taper pin. The inner coil position relative to the taper pin determines the hairspring's neutral position and therefore the balance wheel's rate — an incorrect position produces a movement that runs consistently fast or slow and cannot be corrected to the correct rate without repositioning the hairspring. With the mark made before removal, align the marked position with the taper pin hole and install the pin in the same orientation as before. The movement can then be tested for rate and regulated using the normal rate adjustment, with the knowledge that the base rate is correct because the hairspring is in its original position.

After the taper pin is installed and the balance wheel is running, observe the hairspring coils during the balance wheel's oscillation. The coils should expand and contract concentrically — each coil remaining centered relative to the adjacent coils throughout the full oscillation range. A hairspring that shows one section of coils moving eccentrically, or that appears to breathe unevenly, has been deformed somewhere along its length. Very minor deformation can sometimes be corrected by expert watch repair technicians using specialized tools to gently reshape the affected coil, but this is delicate work that risks worsening the deformation if not done with proper skill and equipment. A significantly deformed hairspring that produces erratic rate behavior requires replacement of the balance wheel assembly.

Taper Pin Replacement Material

When installing new taper pins during reassembly, use brass taper pins rather than steel wherever possible — the dissimilar metal combination prevents the galling that made the original steel pins so difficult to remove. Taper pin sets in graduated sizes are available from clock supply houses and hardware suppliers in both brass and steel. For positions where the pin must carry significant load — such as the alarm mainspring post position where the spring force pushes the wheel against the pin — a steel pin may be necessary as described above, but in those cases installing with a very light film of appropriate anti-galling lubricant on the pin surface reduces the tendency for future galling while still providing adequate retention. For positions where the load is minimal — the balance wheel position and most motion work positions — brass pins are the correct choice both for easier future service and for correct practice that matches the original manufacturing standard.

FAQs

How do I remove the balance wheel from a Junghans Joker without damaging the hairspring?

Remove the balance wheel assembly as the very first disassembly step — before separating any plates or removing any other components. Mark the hairspring inner coil position at the taper pin contact point with a fine permanent marker before removing the pin. Extract the taper pin by pressing on the large end (which faces toward the arbor collar on these movements), allowing the balance wheel assembly to lift free. Handle the assembly by the balance wheel rim or the cock edges, never by the hairspring, and store it in a protected location where nothing can contact the hairspring coils during subsequent disassembly.

Why do Junghans taper pins gall and break when extracted?

Galling occurs when steel contacts steel under the contact pressure of a taper pin in a steel arbor hole. At microscopic contact points, the normal oxide lubrication layer breaks down and bare metal surfaces weld together momentarily. Over decades of a stationary pin in a stationary hole, these micro-welds consolidate into a bond that requires shearing force to break — far more than the pin material can withstand in tension, causing the pin to fracture rather than extract intact. Dissimilar metals (brass pin in steel hole) prevent galling by eliminating the micro-welding tendency. Steel pins in steel holes are sometimes used where the load on the pin requires steel's greater strength, making future service difficult.

What is the correct method for removing a broken taper pin stub?

Use a small dental burr in a Dremel rotary tool at low speed to carefully grind the protruding stub material flush with the arbor surface on the interference side, freeing the component the pin was securing. After removing the component and freeing the arbor from the movement, drill out the remaining stub inside the arbor hole with a drill bit slightly smaller than the pin diameter, then collapse and extract the remaining thin wall as fragments. Clean the hole thoroughly after drilling before installing a replacement pin. Do not attempt to extract a flush-broken stub by drilling in the movement — drill only after the arbor is free and accessible from both sides.

What does the long taper pin on the alarm mainspring post do?

On the Junghans Joker movement, the alarm mainspring is positioned with a portion of the second alarm wheel between the mainspring and the first alarm wheel. As the mainspring unwinds, the inner coils could potentially cone upward into the space where the second wheel is located. The long taper pin on the alarm mainspring post extends above the spring level and prevents the spring's inner coils from migrating upward into the adjacent wheel train, protecting both the spring and the wheel from contact damage. This is a design feature specific to the alarm side's unusual gear train geometry, not a general alarm clock feature.

Can I replace the Junghans Joker mainspring without removing the taper pins?

Yes, if the old mainspring can be cut out from around the still-installed pin. Cut the spring loop at the post end, remove the spring from the movement without needing to clear the pin, and install a replacement open-loop mainspring of the correct width and thickness. The replacement spring does not need to thread over the pin — it wraps around the outside of the post with the pin already in place. Cut the open-loop spring to the correct length and reform the inner hook on the annealed cut end to fit the barrel arbor hook. The long pin remains in place, preserving its coning-prevention function without requiring its removal.

Where can I find replacement mainsprings for Junghans alarm movements?

Measure the original mainspring's width, thickness, and length in millimeters if possible — these three dimensions specify the replacement. The Junghans Joker alarm mainspring is approximately 7.5mm wide by 0.46mm thick. Major clock supply houses including Timesavers carry mainsprings in metric dimensions for German alarm movements; an open-loop spring of 7.5mm by 0.42mm by 1420mm cut to the correct length is a workable replacement. If the original cannot be measured because it was cut out, calculate the theoretical spring length from the barrel's inner and outer radii and the spring thickness, and order a spring close to that calculated length.