As I work my way through my epic stash of “project watches,” I’m excavating some long-buried watches that I worked on years and years ago with cryptic notes. I packed away a bunch of partly assembled watches with “notes to self” when moving a while ago, but I’m not always sure what I was trying to tell myself.
One of them is this post’s watch: a Hamilton “Clinton” wristwatch, likely from the early 1950s. I don’t have a good pre-picture, but I recall buying the watch in rough shape. The dial was a lost cause, so it was sent off to be refinished. I found the new dial, the case, and the assembled movement in some small containers along with this less-than-helpful note: “cleaned, wavy, runs bad.” Hmm… Let’s see what we can do now that some years have passed.
This watch has Hamilton’s 747 movement, an 8/0 movement released after WWII and the start of their line of men’s wrist watch movements that are “wrist watch-y.” Instead of being small pocket watches, with pocketwatch-y features like mean-time screws and precision regulator arms, Hamilton’s wrist watch movements are small, modern, and in some ways much harder to adjust than the older 987 and 982 movements.
Troubleshooting Wavy Traces
I’m assuming I was telling myself that the timing machine traces were wavy. I took apart the watch to troubleshoot the cause of the waviness. As we have explained elsewhere, unstable rates create wavy-looking traces on the timing machine. There are many causes, but the most common cause is a flaw in the gear train, such as bent pivots, worn teeth, or worn pinion leaves.
Time to scrutinize the gears.
They actually look okay, all things considered.
Next up—time to inspect the jewels. Chipped and cracked jewels are a common cause of wavy traces and positional timing errors. Even tiny “flea bite” chips on the edge of a hole will cause problems. The 747 has modern friction jewels without all those fussy pocket watch-y chatons and settings.
These jewels look okay.
Here we go—the center hole jewel for the center wheel has two cracks.
And the wheel after it, the third wheel, has a small chip on the edge of the hole.
When replacing jewels, you can measure them for replacements by measuring the outer diameter and hole size. For watches from the era of interchangeable parts, however, you can usually harvest some jewels from the boneyard. I have a few 747 cadavers I can exhume for jewels.
Here are the cracked ones, pressed out. With pressure, the center hole jewel started to flake off. Even when a watch “runs fine” (i.e., it ticks) with a cracked jewel, eventually the jewel will send rock hard shards into the movement, so it really ought to be replaced.
And here are the grubby donor jewels, which need a good scrubbing before being (literally) pressed into service.
And there we have it, cleaned up and looking good.
As an aside, while we’re talking jewels, the Hamilton 747 has an interesting upper balance jewel system. (This bridge has some alarming gouges, by the way—who knows what someone was trying to do.) To remove the cap jewel, a screwdriver goes into the slot and unscrews a retaining cam.
The endstone cap is fitted with three posts, which are nudged out. The cap can seem “stuck” when the old oil has dried to hard crust.
And here they all are. It’s a clever system that’s secure and easy to clean and oil, but it offers no shock protection.
Not-Quite Adjusting the Movement
After a thorough cleaning, demagnetizing, and a day to run, the watch was ready for its close-up. How well might this little fellow run? Not great, actually. This watch ran fast—not a little fast, but 8 minutes a day fast in all 6 positions. Hmmm.
When a watch runs super fast, you can do some basic troubleshooting. If the timing machine traces are messy and the amplitude is poor, then there’s an escapement problem—it is probably the usual sorts of things you see with old watches, like endshake problems, sticky hairsprings, or a hairspring rubbing a balance arm, bridge, or wheel.
But if the traces are clean, the amplitude is good, and the watch is super fast in all positions—what we have here—then we funnel deeper into the troubleshooting flow chart.
If poise is horrific, we’d suspect that the balance wheel is missing a screw. It does happen sometimes: watches, like people, can often have a screw loose. This shows up as very slow rates overall as well as shockingly bad poise errors in the vertical positions. But this watch was actually pretty consistent in the vertical rates, and all the screws seemed accounted for.
For this watch, then, a few possibilities seem likely:
- a pair of screws is missing
- a pair of screws was swapped for a lighter pair
- the hairspring was damaged and swapped with a hairspring that was originally vibrated for another balance wheel
I suspect the third because it’s just more likely than the others.
The Screwy Nature of the Hamilton 747 Movement
Time to slow down this freakishly fast watch. In its service manual (available here as a PDF), Hamilton discusses the new screws of the 747 movement at some length. It states:
Balance Wheel Screws used in Hamilton Grade 747 are different from those used in any other
Hamilton movement. Like all other screws used in the movement, the balance wheel screws employ a new thread standard. So that these screws will readily be distinguished from balance screws in other Hamilton movements they have been designed with a dog point instead of the cone point commonly used. Under no circumstances should a watchmaker attempt to substitute balance screws on this movement. He will invite difficulties which, under extreme circumstances, may make it necessary to replace the balance wheel.
In short, don’t even think about sticking a 987A screw on there! Indeed, the screws are pretty different.
The picture doesn’t quite do the screws justice. In real life, the threaded shaft of the screws are slightly conical instead of cylindrical. Notice the taper from the barrel-shaped screw head to the tip.
Why are we going on and on about these screws? Because they are conical, the threads don’t fully grip until the screw is nearly all the way in the hole. This doesn’t matter except that it makes is impossible, in many cases, to add timing washers.
Timing washers, as mini spacers, displace the screw away from the balance wheel. For normal cylinder screws, it doesn’t matter—they will thread normally. For these 747 screws, however, some of them won’t engage the threads—they’ll simply spin and spin as if they were stripped. Even smaller timing washers can displace the screw too far for it to grab the wheel. Weird.
Through a maddening process, I’ve found that some 747 screws, depending on what is probably random variation in their length and tap/die process, will accept timing washers, but many won’t. For this balance wheel, no opposing pairs of screws will both securely hold timing washers. Curses.
So we need to slow down this watch, but timing washers won’t do the trick. An alternative is to replace two current screws with slightly heavier ones. Time to go back to the boneyard and find a scrap balance wheel.
I inspected the screws to find two that seemed relatively heavier. These screws seem to have different screw slot depths, so I picked two with relatively shallow slots and used them to replace two screws with relatively deeper slots.
That did the trick—my guesstimation of screw size was accurate, and the watch was -100 seconds slow a day afterward. I can work with that.
The next day I nudged the regulator and measured the rates in all 6 positions, and here’s what we have—pretty good!
For the 5 main wristwatch positions, all the rates are reasonably close. One rate (pendant right, PR) is way off. As the old watchmaking books say, the timing error appears to have been “thrown into the 6th position.”
I’m going to leave well enough alone. I’m exasperated with this little watch, and this is a good outcome. Time to work on the case, the topic of part 2!