Adjusting a 1948 Hamilton “Dyson” 747 8/0 Wristwatch with Bad Amplitude

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Moving from one house to another is always irksome, but it really hurts when you work on watches. Moving a big couch is easy; moving a dozen small watches in various states of disassembly is another matter entirely.

I moved a year or two ago, and I packed away and stashed a batch of Hamilton wristwatches that were mostly done. One of them is this little watch: a Hamilton “Dyson.” Dan at Hamilton Chronicles, as usual, has a nice overview of the Dyson model, which is ubiquitous on eBay.

I love the dial on this one. I has a nice, even toning that looks great on a vintage watch. There are no refinishing marks on the back, so I think it is original.

The Dyson has the 17-jewel 747 movement, one of my favorite wristwatch movements. It’s easy to work on and attractively finished. This movement appears to be from around 1948 according to the inestimable Pocket Watch Database.

I feel bad picking on Elgin, but there are reasons why people don’t collect Elgins from the late 1940s and early 1950s—their watches just aren’t visually appealing compared to Hamilton’s watches of the time.

I had left myself a cryptic note with the packed-up watch: “cleaned, poise good, persistent bad amplitude.” Apparently I had worked on this watch already. So I fired up the timing machine and found that my note was right: the amplitude was bad.

In the horizontal (or lying) positions—dial up (DU) and dial down (DD)—the amplitude wouldn’t get over 220 degrees. And it was much worse in the vertical (or hanging) positions. But the timing traces were stable and clean, so nothing was scraping or rubbing.

Causes of Poor Amplitude in a Clean Watch

Watch adjusting is all about good amplitude, so we need to fix this before adjusting the watch to positions.

When a dirty watch has bad amplitude, there’s no need to troubleshoot or diagnose: just clean and service it. But when a clean watch has poor amplitude with clean traces in all 6 positions, some pondering is necessary.

Many things cause poor amplitude. A few are obvious:

  • an old, tired, or set mainspring
  • an incorrect mainspring, usually one that is too too weak (doesn’t deliver enough power) or too wide (binds against the barrel and cap)
  • poor balance staff endshake (the bridge presses down against the staff)

A few are more subtle:

The Curse of Endshake

The problem turned out to be unusually subtle—not enough endshake on the escape wheel. The wheels in the gear train should always have a slight endshake, meaning they can be lifted straight up and down, albeit very slightly so.

When the endshake isn’t enough, the bridges bind against the shoulders of the wheel, increasing friction and preventing them from spinning freely. I suspect that the escape wheel was replaced at one point. Parts weren’t completely interchangeable back in 1948, so the new wheel probably didn’t fit as well as the old one.

For this little Dyson, the gear train would spin freely when the center wheel was nudged, so the binding wasn’t huge, but the endshake was poor enough to act as a brake on the escape wheel, reducing the amplitude.

So, to the jeweling set! We can adjust the endshake by pushing on one of the escape wheel’s jewels to make more space. But which one? I could see that the escape wheel’s teeth hit the lower half of the pallet jewels when dial down. Pushing the lower plate jewel would make the escape wheel sit even lower and thus hit the pallets near their bottom edge. So, we should push out the upper bridge jewel instead. This will keep the escape wheel’s teeth near the sweet spot of the pallet jewels. (If you’re just getting into friction jeweling, Fried’s book Bench Practices… is the best place to get started.)

The bridge jewel was 1.40 mm in diameter, so we need a pusher that is nearly as wide. I picked a 1.25 flat pusher.

You start by lightly pressing the flat pusher against the jewel. The pusher must be exactly centered in the jewel. This establishes the jewel’s current depth. Then you rotate the stop collar so that it stops the plunger at that point. In short, the jeweling tool is set up so that it can’t push the jewel in any farther than it already is.

In the photo, you can see the markings on the collar. To adjust the endshake for this wheel, I rotated the collar by 8 units. This allows the handle the move the plunger down ever so slightly, which of course pushes the jewel down ever so slightly. Voila!

Now you can see that the escape wheel jewel, in the foreground, is set very slightly deeper that the fourth wheel jewel. The difference is slight—you would’t notice it if you weren’t looking for it—but it’s enough to give the escape wheel the right endshake.

And that did the trick. When the watch was put back together, the amplitude was over 270 in the lying positions and 220 in the hanging positions. It isn’t as high as I’ve seen on other 747 movements, but it’s enough.

I wound the watch and checked the rates, and the old note to myself was right: the poise was pretty good.

For a small 8/0 wristwatch, these are great rates. No one position is too far from any other. The biggest difference is 13 seconds, and most of the positions are fairly tightly clustered. The timing traces are a bit wavy—common in these old Hamilton wristwatches—so you can add +/- 4 seconds to each rate, more or less.

I don’t remember if I did some preliminary adjusting a couple years ago or if this watch is simply a good watch. After nudging the regulator to set the rate to slightly fast, I decided to leave well enough alone.

Cleaning the Case

The Dyson has a gold filled case, and this one is in nice shape.

There’s a bit of wear-through on the lugs, and the surface has the usual swirls and scuffs.

From a metalworking perspective, there isn’t much you can do with gold-filled cases. The gold is many times thicker than plated cases, but it’s too risky to polish the case as you would a solid gold case or stainless steel case. A compound that cuts the metal, like a tripoli compound, would cut through to the base metal quickly.

The main goal is to remove the haze and shine it up. I first clean the case in the watch cleaning solution, which does a nice job of removing the built-up oils and film.

And then it’s Foredom flex-shaft time. With a small cotton buff and Dialux red compound, it was easy to get this case looking great.

The case is much brighter and sharper.

And with the movement in and a fresh acrylic crystal, this Dyson is looking great and ticking away nicely.

But in a final indignity, when I tried to put a band on it, I realized the Dyson is one of the dreaded 17 mm lug-width cases. 17 mm bands were popular in the late 40s and early 50s, but I don’t have any bands in this oddball size. Grrr.