It is much easier to work on fine watches than mediocre ones. High-grade watches were made with service and repair in mind, they left the factory in excellent condition, and they are usually expensive enough to discourage beginning hobbyists from fiddling with them.
Enter the Illinois Bunn Special, a classic and charming watch. One of Illinois’s old advertising slogans was Illinois watches are better than they have to be, and that’s certainly true.
I recently picked up this 16-size Bunn Special from a pawn shop. One rarely finds nice watches in such places, but I got an excellent deal on this one. This watch is from 1923. It has 21 jewels and a conventional barrel (i.e., neither 60 hour nor motor). It wasn’t running, but I thought it had excellent potential—the movement looked clean and had a good balance.
Before adjusting a watch, it helps to step back and consider the factors that would make it easier or harder. This gives us a sense of what accuracy level we could realistically aim for.
This watch has many good omens:
- It’s an Illinois Bunn Special, people. It left the factory adjusted to 6 positions by the best adjusters in the business.
- The watch is unusually clean. It has very few marks and scuffs from screwdrivers and tweezers, so it probably hasn’t been fiddled with much.
- There are no timing washers or signs that the balance screws have been modified. (They could have been undercut, of course.)
And there are some dark signs:
- The watch was missing its dial washer and a case screw—classic signs of having been messed with by someone inattentive.
- The dial feet look like a muscle-bound watchmaker tightened the screws in the midst of anabolic ‘roid rage.
- I probably have bad watchmaker karma for being, shall we say, not entirely straightforward with the seller. I got a great deal because the pawn shop employee knew little about pocket watches. He said it wouldn’t wind up, which was true because the mainspring was broken. But he also said the hands wouldn’t set because “the crown is stuck on this one and won’t pull out.” I wasn’t about to tell him that these watches are lever-set, and I made a low offer out of concern about how much it might cost to repair it.
As always, we started with a thorough cleaning and oiling, a new white alloy mainspring, and a visit to the demagnetizer. I set the regulator to the middle of the index and let it run overnight. The watch’s amplitude was excellent: at least 300 degrees in all positions.
The next day, here’s what the rates looked like at full wind. As a baseline, this is really quite good:
- the rates were dead stable on the timing machine—completely clean, parallel, and steady
- the dial up and dial down positions had essentially identical rates and amplitudes, which I don’t often see at the start
- all the positions are reasonably close together
Adjusting Without Removing Weight
For this watch, I wanted to adjust it without removing weight—no undercutting or filing. I am not philosophically opposed to removing weight, of course, but I do view some watches from a historic preservation lens. Unlike filing and undercutting, adding timing washers is reversible. Really fine adjusting—getting all the rates to within a few seconds, such as our Hamilton 987A Bagley and Illinois 12s 405—usually requires removing weight, so we should set our accuracy goals lower. For this watch, I’m willing to trade slightly worse positional rates for keeping the watch in its original condition.
We’ll dig into adjusting without removing weight in a later post. In brief, the only real issue is to ensure that the horizontal and vertical rates don’t diverge. Adding weight will eventually make the watch run slow dial up and down. At this point, we set the watch to run fast again by screwing in the mean time screws. This allows us to add more weight in a way that also aligns the horizontal and vertical rates.
This watch is already running fast, so we start the process of dynamic poising. When amplitude is low, around 130 to 160 degrees, poise errors have bigger effects on rates. Because a watch will run fast when the heavy spot is below the balance staff, we can measure the rates in all 8 positions and find the one that is the fastest. The heavy spot is below the staff in that position.
Here are the rates in all 8 positions. The fastest position is pendant left, +128 seconds a day. (Recall that PL and PR are defined from the dial side, but we’re viewing the movement side.)
So, when the watch is in this position, the heavy spot on the balance wheel is directly below the balance staff.
We can zoom in on the wheel to see the heavy spot. The yellow line shows the vertical line through the staff. The red spot is the heavy spot; naturally, the green spot on the opposite end is the light spot. Conveniently, there is a screw at each spot.
Because the watch is running fast, we will add weight to the light spot. This will improve the balance wheel’s poise while also aligning the horizontal and vertical rates.
We add weight with timing washers. Choosing the right washer involves some intuition and experience. I have been hoarding a huge stash of timing washers—it helps to have a lot. In the assortment below, the washers are rated for different pocket watch sizes.
I have a 16 size watch, but the 18-16 washers would be too heavy. The wheel’s poise is pretty good, and my intuition tells me that the light spot would then become the heavy spot. I decide to go with a washer from bottle 5: the lightest washer available for 12-6 size watches. I remove the screw at the “green spot,” place the washer over the threads, and reinstall it. Curiously enough, I could tell that someone had lightened the screw at some point. The slot was wider and deeper than the others—it was a clean job, perhaps original to the watch.
What effect did our light washer have? I wound the watch back to full wind and measured the rates. Here’s what we got.
Oh my. Adjusting is iterative, but sometimes one round is enough. These are excellent rates across all 6 positions. I could get them tighter if I were willing to remove weight—it is easier to remove a tiny amount than add a tiny amount—but I’m sticking to my “don’t add weight” approach.
I thus slightly shift the regulator to make the watch run at +2 dial up, and we’re done.
I suspect that all I did here was compensate for higher amplitude. When the watch left the factory, with its weaker blue steel spring, its amplitude was probably notably lower. With modern springs and lubricants, the watch’s amplitude is probably much higher now. As we saw in a recent post, this can cause vertical rates to shift when amplitude surpasses the neutral zone of 220 degrees.
And here it is, ticking away happily.
In some ways, this watch is a bad example of what adjusting vintage watches looks like: it was too easy. You rarely strike gold after only one round of adjusting.
But in other ways, it is a good example: fine watches are easier to adjust than mediocre ones. This watch left the factory in excellent shape and probably wasn’t meddled with much since then, so it shouldn’t need more than minor tweaking.