Amplitude Troubleshooting Guide
Amplitude is the life force of a mechanical watch — when it fades, everything else follows, and most watches simply won’t perform their basic function — timekeeping — accurately or reliably without good amplitude. This brief troubleshooting guide is by no means exhaustive, but it covers some of the more common causes of amplitude issues I have encountered when working on vintage watches, along with potential solutions.
Prerequisites: The Basics
If you can't get a watch movement running with a healthy level of amplitude (across all positions), it will not regulate properly and will not run with consistent accuracy during normal use. If the movement is in good mechanical condition, you generally shouldn't have too much trouble achieving a solid amplitude level (250+ degrees), particularly after proper cleaning and lubrication.
This guide assumes that you have performed a service and have ruled out some of the more basic and obvious source of amplitude issues. For example:
The movement has been properly cleaned and lubricated.
The mainspring appears to be in good condition and you are able to fully wind the watch.
The wheels in the drive train a rotating freely, without excessive friction.
The pallet fork is rotating freely, engaging properly with the escape wheel and demonstrating good impulse response when manually ticked over.
The balance appears to be oscillating freely, with no obvious obstructions.
Occasionally, however, you may find that, even after reassembling and lubricating a movement with no obvious issues, it is still running with low or inconsistent amplitude, either in specific positions or across all of them. If that's the case, more investigation and troubleshooting will be required to identify and address the underlying issue(s). We’ll dive into this troubleshooting process in the following sections.
This troubleshooting process assumes that you have a timegrapher and can use it to measure the amplitude of your movement. While experience will give you the ability to roughly assess the amplitude of a watch by simply observing the balance, you really need a timegrapher to make precise measurements and to ensure you’ve truly fixed any underlying amplitude issues.
Checking the Balance
The balance is the beating heart of a watch. In my experience, in practice a large majority of amplitude issues can be traced to some sort of impairment of balance function, so a careful examination of the balance is usually a good place to start your diagnosis.
The Hairspring
Just as the balance is the most likely culprit behind amplitude issues, the hairspring tends to be the most likely suspect when the balance is the problem. Here are some common issues to look for:
Sticky Hairspring: A hairspring with even a tiny amount of residual oil contamination or magnetism can stick to itself, causing impaired balance oscillation and low amplitude. Try your demagnetizer first to see if it clears the issue. However, be aware that using a demagnetizer can temporarily free contaminated hairspring coils, in which case the problem will likely recur. If contamination is suspected, remove the balance and carefully push the coils together using a pair of (demagnetized) tweezers. Do they spring immediately apart, or do some of the coils stick together? If you notice any tendency for them to stick together, you will need to clean the hairspring more thoroughly. I like to soak the entire balance in clean bench solvent for several hours, which will usually clear up the problem. Of course, this means you will need to re-lubricate the upper balance jewels, unless you remove the balance from the balance cock beforehand, so I will often do this proactively as a preventative measure before lubricating the movement. I keep a relatively large container of clean solvent handy for this purpose.
Improperly Located Hairspring: Make sure the hairspring is properly located following installation of the balance. Is the hairspring sitting correctly in the regulator? In some compact movements with tight clearances, outer coils of the hairspring are designed to sit below the center wheel, but during balance installation it can be difficult to ensure that coils of the hairspring don't end up sitting on top of the center wheel instead, where they will rub and severely impede the balance's motion. If this happens, you can use a pair of tweezers to carefully nudge the hung coils off of the upper surface of the center wheel, freeing them.
Incorrectly Positioned Hairspring Stud: The hairspring stud generally allows for a small range of different vertical positions when held in the stud carrier. If it is positioned incorrectly (too high or too low), it can cause the hairspring to interfere with other elements of the balance assembly - for example, rubbing against the bottom of the balance cock or bottom of the center wheel (when sitting too high), or top of one or more of the balance wheel arms (when sitting too low). These issues may manifest only when the movement is in specific positions. For example, if the hairspring is sitting too high, it may work fine dial-down but start to rub when the watch is placed in the dial-up position. If you suspect this is an issue, you can loosen the stud screw and manually adjust the stud position to try and correct it. However, if the hairspring itself is distorted (see below) this might not work.
Distorted Hairspring: Distortions or kinks in the hairspring itself can cause significant amplitude issues. These can affect the amplitude performance in various ways, either directly (when sufficiently severe), or indirectly, by causing interference issues (much like an incorrectly positioned hairspring stud). Visually inspect the hairspring both from above and from the side. From above, you should observe coils that are evenly-distributed around the balance staff axis. From the side, the hairspring coils should be sitting on a flat plane, perpendicular to the balance staff axis, that is clear of any obstructions. If this isn't the case, hairspring correction may be in order. I perform these corrections with a pair of fine, bent-tip tweezers under microscope magnification. If you undertake hairspring correction, bear in mind that you may need to make deliberate corrections in both the horizontal plane (by bending) and the vertical plane (by twisting), and that most distortions tend to occur near the "fixed" points: the stud, collet, and regulator. While small adjustments — particularly close to the stud — can sometimes be made while the balance "in situ", you will generally have to remove the balance from the cock to make hairspring adjustments. Removing the hairspring from the balance staff can also be helpful, but I have found that it isn't strictly necessary. As you are making corrections, consider all of the elements of the hairspring's geometry: is the stud sitting at the correct distance from the balance staff axis? Is the stud's vertical axis parallel to the balance staff? Does the hairspring line up properly with the regulator pins? There's a lot to consider, and hairspring correction takes a lot of patience and practice; over time you will develop a certain amount of mechanical intuition that help you judge how to proceed and what corrections to make. Frankly, I hardly consider myself an expert, although I have been able to successfully correct problems in many cases. It's often worth a try, however, since the alternative usually involves sourcing an entirely new balance. Keep in mind that hairspring adjustments will generally throw off the beat, so it's best to ensure that the hairspring is in good shape before performing final beat error corrections.
Loose Hairspring Collet: While it's uncommon (at least in my experience), a loose hairspring collet can certainly cause amplitude issues. This isn't something I look for right off the bat, but if the collet is loose, it will almost certainly throw off the beat, and become very obvious when beat error adjustments are attempted. I like to tighten these using a pivot vice, which allows me to keep the hairspring out of the line of fire.
The Balance Pivots
After hairspring issues have been ruled out, the next most likely culprit is usually the balance pivots and/or jewels:
Dirty or Damaged Balance Jewels: Inspect the jewels carefully under magnification for any signs of contamination or damage. It can take a good deal of persistence to get these jewels genuinely clean, so you may have "missed a spot" on your first pass. If one of the jewels is damaged, it will need to be replaced.
Improperly Lubricated Balance Jewels: Double-check your lubrication. While the balance is installed, inspect the cap jewels under a microscope to make sure you see a clear, appropriately-sized oil meniscus under the cap. If the oil level is insufficient, either because you didn't apply enough oil or because you applied too much (which can cause the oil to end up getting siphoned out of the setting), it will negatively affect amplitude, particularly when the watch is in the horizontal positions.
Damaged Balance Pivots: Inspect the balance pivots under a microscope, looking to see if they are nicked, corroded, or bent. Nicked or corroded pivots can sometimes be addressed by polishing (e.g. using a jeweler's polishing stick or burnishing tool). A slightly bent pivot can sometimes be carefully straightened using a staking set, pivot vice, or a dedicated pivot straightening tool, but this is extremely delicate work, so replacing the balance staff may be a better/more realistic option, unless replacements for the movement you are working on are unavailable or excessively expensive.
Loose or Misaligned Jewel Settings: Loose or improperly seated jewel settings can cause amplitude issues, either by allowing misalignment of the balance staff or by allowing excessive vertical play resulting in clearance issues for the hairspring or other components. Make sure shock springs, for shock protected balances, are in good shape and providing sufficient tension to seat the jewels correctly. For older, non non-shock-protected settings, make sure the screws are properly tightened. Lower cap jewel settings in these old movements are often held by a single screw and can sometimes become slightly bent or distorted, which prevents them from seating properly against the hole jewel. Attempts to over-tighten the screw to compensate for this can easily strip these small screw settings (something I have encountered on more than a few previously-serviced movements). Upper settings on these movements are typically held by a pair of screws which must be torqued evenly to prevent the cap jewel from sitting at an angle relative to the balance staff.
The Impulse Mechanism
If the hairspring and balance pivots/jewels appear to be in good shape, the next area to investigate is the impulse mechanism. This is where the watch movement actually transfers energy from the gear train to the balance, so any issues here can significantly impact amplitude. Common issues to look for include:
Debris in the Pallet Fork: Inspect the pallet fork where it engages the impulse jewel. Make sure all of the surfaces are clean and free of debris (If need be you can clean it with some Rodico). Is the pallet fork guard pin properly aligned? If not, it can interfere with the impulse jewel or other parts of the mechanism.
Impulse Jewel Or Roller Table Issues: Check for a loose, damaged or misaligned impulse jewel or roller table/safety roller. Loose parts here prevent efficient energy transfer, while misaligned parts can cause interference issues or prevent proper engagement with the pallet fork.
Banking Pins: Occasionally you will run into a movement with banking pins that are out of alignment. This can sometimes allow excessive travel of the pallet fork, which impairs energy transfer, and carefully tightening/aligning the pins can help address this. Don't go crazy however, you don't want to over-tighten the pins, and the pins should only be serving as a "soft" limit on travel: If that's not the case you probably have an issue with the other end of the pallet fork, where the pallet stones engage the escape wheel, and you may need to adjust the lock by moving the stones.
Pallet Fork Wear: The pallet fork is made of hardened steel, so wear at the interface with the impulse jewel should be negligible under normal circumstances. However, if there is significant wear at that point (possibly from grinding action due to microscopic contamination), it can reduce the efficiency of energy transfer and impact amplitude. Traditionally this could be addressed by installing a slightly larger impulse jewel, although I think replacing impulse jewels in this manner was somewhat rate outside the pocket watch world. Alternatively, as a last resort, before replacing the pallet fork, you can try to tighten the fork end (e.g. with a staking set). This is pretty difficult to pull off without damaging the fork, but it's worth a try if the only alternative is replacement.
The Balance Wheel
The balance wheel itself is a less common source of amplitude issues in my experience, but when you have ruled out other possibilities, it's worth looking at
Out of Poise Balance Wheel: An out-of-poise balance wheel can cause the balance pivots to ride with excessive force against the side of the hole jewel, increasing friction and reducing amplitude. You can observe this by carefully viewing the pivots under a microscope while the watch is running, but if you suspect this is an issue you should check, and if necessary correct, the poise of the balance. This requires a specialized poising tool.
Damaged Balance Wheel: A bent or warped balance wheel can cause a multitude of issues. If the physical tolerances of the balance assembly are tight enough, it can even cause the balance to rub against bridges or other components, which obviously has a great effect on the amplitude. Fortunately, this sort of damage is rare, unless the balance wheel has been subjected to significant shock or mishandling (this can occur, for example, during balance staff replacement). It is generally pretty obvious under close inspection.
Beyond the Balance: Other Sources of Amplitude Loss
Let's leave the balance behind and work our way back up the train toward the mainspring. Once you have ruled out balance-related amplitude issues, here are some other things to check:
Pallet Fork and Escape Wheel Issues: As noted above we're operating under the assumption that the pallet for is demonstrating a strong impulse, or "kick," when cycled. However, since there's no way to really measure the strength of this impulse, it can be worthwhile checking the pallet fork and escape wheel interaction to make sure there are no evident problems. Make sure the pallet stones aren't loose, and that they are aligned properly. In some cases you may need to reposition them, potentially moving them outward slightly (toward the escape wheel) to enhance the "lock" and get a stronger impulse. This can be done by heating the shellac holding them until it softens, but it is definitely delicate work, and something I have only personally attempted a few times. While you're at it, check the escape wheel teeth to make sure they're not damaged or excessively worn. Finally, double check your lubrication in this area (You did lubricate the pallet stones, right?).
Gear Train Issues: If one or more of the wheels in the gear train isn't rotating freely, it will definitely affect the amplitude. That's why it's important to verify that the train is spinning freely after you replace the bridges, and to inspect the pivots and teeth of all of the wheels before you reinstall them. Often, these wheels will exhibit periodic increases in friction as they rotate, which will show up in the timegrapher as an oscillation in the amplitude over the same period. Usually the periodicity of this amplitude change will match the rotational rate of the problematic wheel, but if the issue is being caused by a specific interaction between the teeth of two wheels, the period can be substantially different.
Clearances: Some watch movement designs have elements in the moving gear train that can have very tight clearances, which can cause intermittent friction or binding if there is any dirt, debris, or slight deformation. One example is certain movements with an indirect-drive center seconds pinion driven by a friction fit intermediate wheel attached to an extended 3rd wheel pivot. These often have very tight clearances in order to keep the overall movement as thin as possible, but it means that a slightly bent wheel or pivot, or a wheel that simply wasn't press fit at the correct height, can cause rubbing and friction that impact amplitude. Misbehaving or misaligned hacking mechanisms can also cause similar issues. Inspect the entire movement carefully from multiple angles to look for potential clearance issues.
Sticking Mainspring Arbor: One of the "forgotten" rotating components in a watch is the interface between the mainspring arbor and the mainspring barrel. This is a high-friction metal-on-metal interface which must rotate freely in order for the mainspring to unwind properly and deliver power to the gear train. It's also tricky to assess when you're reassembling the movement, since, when you test for a free-spinning gear train without the click installed, the barrel and arbor can spin together in the arbor pivots. In any event, lubrication of this interface should not be an afterthought. I like to place a bit of 1300 on the circular "lips" where the arbor contacts the barrel body and lid, before inserting the mainspring or the lid, respectively. I also then follow up by applying a bit more 1300 to the arbor interfaces from the outside once the barrel is fully assembled.
Improper Braking (Automatics): Automatic mainsprings have a bridle that is designed to rotate around the mainspring barrel when a level of tension corresponding to a full wind is reached. This is facilitated by application of a small amount of high-viscosity "braking" grease to the inner barrel walls, but if this grease has too much lubricity, or if an excessive amount is applied, it can prevent the mainspring from reaching full wind before slipping, which will naturally reduce amplitude. If you suspect this is an issue, you can try cleaning and relubricating the mainspring and barrel. Use braking grease sparingly; I typically place 5 small spots around the inner barrel wall before inserting the mainspring. If you're still getting excessive slip even after careful relubrication, consider switching to a heavier grease with stronger braking action.
The Mainspring: Swapping the Engine
Finally, if you have ruled out all of the above issues, it's time to consider the mainspring itself. A tired mainspring simply won't be able to supply enough power to drive the movement with good amplitude, even if everything else is working perfectly. Mainsprings are inexpensive and pretty easy to replace, so, while I usually check for other issues first, for some folks it may be more of a first step than a last resort. You can even consider using a slightly stronger-than-stock mainspring to compensate for certain otherwise-intractable amplitude issues, but don't overdo it, since an excessively strong mainspring can cause overbanking or push other delicate components beyond their design limits. In general, it's best to stick with a mainspring that is as close to the original specifications as possible. Just bear in mind that a mainspring will impact amplitude more-or-less evenly across all positions, so if you have position-specific amplitude problems, you will still need to find other methods to address them.
Consider the composition of the mainspring as well when considering replacement. Older carbon-steel mainsprings (typically dark brown, grey or blue, with a single spiral wind) might be worth replacing in a watch that is intended for everyday wear, even if it's still delivering good power, simply because modern "white alloy" spring deliver more consistent performance over time and are less prone to breakage.