Amplitude is the watch adjuster’s friend: we want amplitude of at least 270 degrees in the horizontal positions and 220 in the vertical ones. If we don’t have that, the watch isn’t ready for adjusting.
But you can have too much of a good thing. When amplitude is too high, you get knocking. An amplitude of 270 means that a point on the balance wheel is turning 3/4 of a full circle. As amplitude hits 360, the wheel is making a full rotation, and you’ll likely get knocking.
The balance wheel can only rotate so much. At a point, the balance travels so far that the roller jewel bangs against the other side of the pallet fork. This banging sound is usually audible. Instead of ticking and tocking, the watch sounds like it is galloping.
Knocking is really bad, and we can’t let a knocking watch run for long. The rate will be freakishly fast, as the wheel careens from one end of the pallet to the other, and this is how roller jewels get broken.
So how do we identify knocking, and how do we fix it?
Knocking’s Timing Signature
Knocking is easy to spot on a timing machine. Usually, you’ll see something like this, which is from a 12s Illinois pocket watch:
Notice the clean, parallel lines that get interrupted by staccato, noisy periods. What is happening is that the balance is building up amplitude during the clean period, and then amplitude gets high enough to knock. The knocking reduces the amplitude enough for the escapement to find its footing, and the cycle continues.
When knocking is severe, however, you might see only “timing noise”—the dreaded cloud of dots on the timing machine. So, to properly diagnose knocking, we need to do a second step. Many, many things cause noisy timing traces, and we need to rule most of them out.
For step 2, let down the power from the mainspring, wind the watch to around 20%, and then observe the timing traces as the watch runs. Because the power from the mainspring is much lower, amplitude will be lower. So, if knocking is the problem, the traces should be clean and stable when the watch runs at low wind. If something else is the problem—hairspring rubbing, a bad foot on an escape wheel—the traces will still be noisy at low wind.
Why is Knocking Common?
Knocking is pretty common, perhaps much more common than in the past. Modern methods of servicing watches both reduce friction and increase force, causing much higher amplitude than the old-timers usually saw.
On the friction side, modern cleaning solutions and methods can get jewels and pinions surgically clean. Compared to the old benzene, horsehair brush, and box-of-sawdust methods you read about in the old books, the newer methods are miraculous. Likewise, modern lubricants—especially oils for pallet jewels, like Moebius 9415—will do wonders for amplitude.
On the force side, modern white alloy mainsprings are the real deal. Vintage watches from the earlier half of the 1900s were designed with blued steel mainsprings in mind. These would “set” (lose their elasticity and form into a spiral shape) quickly and break often. White alloy mainsprings, in contrast, don’t become “set,” and they deliver force more consistently. Newer ones are Teflon-coated for even less friction.
A mainspring’s strength is expressed in its thickness. In the old days, repairers could choose from a range of mainspring strengths, from weaker (for a lower-friction 19 jewel model) to stronger (for the 7-jewel brass bushing budget model). The modern adjuster, however, usually has only 1 option, which may be the strongest one.
Taken together, the stronger mainsprings, cleaner watches, and better lubricants can crank up the amplitude, so we’ll see knocking often.
Another reason for knocking, however, comes from past repairer’s fiddling with the escapement. Manipulating the banking pins and the depth of the pallet jewels will greatly affect amplitude. Hobbyists and repairers alike won’t often slide pallet jewels in and out to modify amplitude, but a certain sort of person just can’t resist the urge to fiddle with the banking pins. When the watch reaches you, it might be set up improperly.
How to Unknock a Watch
Knowing the causes of knocking clarifies our options for fixing it. In short, we need to reduce amplitude.
- The first step is to evaluate drop-to-banking of the pallet (see Fried’s The Watch Escapement or Kleinlein’s book for details). If necessary, reset the drop to banking.
- If the escapement is properly set up, the next step is to swap the mainspring for a weaker one, if that’s an option—in most cases, it isn’t.
So that leaves us with some sordid and unseemly methods, ones that are, shall we say, looked upon unfavorably by a large segment of people who hang around the NAWCC message boards. These methods are frowned upon because they introduce a fault or go against good practice.
- remove and clean the pallet, and then underoil it
- use heavier oil for the escape wheel or balance wheel
- lubricate the pallet arbor jewels
These do seem sordid, but we can’t let the perfect be the enemy of the good. A knocking watch is unusable, after all, because it risks breaking the roller jewel. When we have to weigh having a watch we can safely wear against the standards of pure and proper practice, hopefully we can agree to be practical.