Where it’s from
This watch was given to me by my aunt-in-law, and used to belong to her father, my wife’s grandfather.
I found what looks to be the exact same watch (in steel, instead of goldplated) on eBay, and it’s listed as from the 1970’s. However, the dial on this watch is radioactive, so it was either made earlier than that, or the dial is tritium instead of radium. The Gieger counter is pretty chatty, so I think it’s actually radium.
What it looked like
The watch seems to be in relatively good condition, with minimal scratching. The hands can be set, and the movement can be wound. I can also hear that the automatic rotor inside is spinning freely, and is also able to wind the movement. It seems to be gaining some time, but the trace is dead straight, so I’m guessing the movement is in excellent condition inside.
This will be the first movement that I’ve worked on with a radium dial, so I’m a bit nervous.
How I restored it
May 6, 2026 8:38 PM
I took a deep breath a couple of days ago, and attempted to open the case. However, try as I could, the back would not come off using the rubber ball. So, I went ahead and ordered a screw-on case back remover tool. Should get here in a couple of days.
In the meantime, I started looking at the bracelet. It seems to be in pretty good shape with just a few loose links, but I notice that there appears to be some kind of bracelet extender that is missing a spring:
I can’t really make heads or tails of this. I took it off the clasp, and there’s definitely no spring inside the narrow box. I bought what looks like the same bracelet on eBay, maybe it will have some clues (and potentially spare parts!)
I also addressed some of the loose links, with the judicious use of a toothpick:
May 9, 2026 7:30 AM
Forgot to put an update here. I bought a cheap two-prong case back opening wrench. Take a look at how it went:
In addition to the wrench breaking, I put a huge scratch in the case back, and a smaller one on the actual case. Under the advice of the watch repair forum, I’m buying a 5700-style case back opener that has a built-in vise holder and handle. Hopefully that does the trick!
May 16, 2026 5:41 PM
The case back tool came in. Success!
Some notes from the opening:
- The case back was really, really tight. Looking at the threads on the case back, I see a lot of what looks like metal shavings. Could it be that it had something to do with it?
- The gasket was very brittle, and immediately crumbled when I took it out.
- No watchmaker’s marks, and the movement is extremely clean. I am betting I am the first one to open this up!
- The dial bezel was actually a separate piece, held between the case and the crystal.
- The movement clearly says “731CA”, but Emmywatch and others show the caliber as the Gruen 730CA. Perhaps there was a short run of the 731CD that featured only the date.
Getting the crystal off was a bit dicey. I tried using the crystal lift, but it wasn’t getting it to release. So, I firmly but gently pushed the crystal from the inside of the case, and it eventually came free. However, it looks like I chipped the crystal a bit with the lift:
Normally this wouldn’t be such a big deal since I would just replace it. But this crystal holds the dial bezel in, so it has a special small rabbet on the inside edge which most crystals don’t have. Sourcing a replacement might be tricky, since the size of the rabbet I am guessing is custom to this watch.
The movement is running pretty well. I think I may not actually give it a full service, and just address the regulation and the case. I have a slight worry that I munged the keyless works somehow though, as the stem no longer engages with the setting lever.
May 18, 2026 6:39 AM
I decided to go ahead and do a full service on this, so I spent some time yesterday starting the disassembly. I’m glad I did, because when I took a close look at some of the jewels, I could visibly see some very old, dried on oil:
I removed the calendar, motion, and keyless works, and then flipped over the movement to the train side. I removed the automatic works, and then realized that I had forgotten to take the power down. Rather than re-install the keyless works to do this, I decided to just call it a day, and let the movement run down on its own. Surprisingly, I had wound it the day before, and it was still going strong, so perhaps the 45 hour power reserve reported by Emmywatch is actually accurate, ha. Here’s some photos of the disassembly:
One other interesting thing to note: it looks like the automatic works only wind in one direction, as I see what looks sort of like a click on one of the automatic winding wheels. And, none of the wheels in the automatic works appear to be reversible. I also had a bit of a scare when taking the cover plate off for it, since I heard a ping. There’s a relatively beefy spring that keeps that first wheel/pinion under tension against the larger wheel, and I think when I released the plate, it pushed it to the side. I see a deep scratch in the plate where that wheel sits, so either it was from me doing this, or it was already there. It certainly didn’t sound violent enough to make that scratch, but given that I’m almost sure this has never been worked on, I don’t know what else could have done it.
I also saw what looked like a dent on the small bridge holding that third automatic wheel in place. It’s possible that’s intentional, since it looks more like a spring than a bridge (there is no pivot), and that it is bent down to hold that wheel in place.
May 19, 2026 6:19 AM
Just a very small update from last night: took out the balance and pallet fork. They both look to be in excellent shape.
May 19, 2026 8:18 PM
Another update, from this morning: I finished disassembly. Everything looks great, although the jewels are definitely grimy:
Jun 13, 2026 7:58 PM
Starting to prep everything for the wash. Some notes:
- The cap jewel for the escape wheel on the 3/4 bridge has a strange retaining ring, instead of a spring. Also, the housing for the holed jewel is fixed in the bridge
- The cap jewels for the balance seem to be ever so slightly different. The cap jewel on the plate seems a tiny bit thinner than the one on the balance bridge.
- There was a plate covering the gear in the automatic works, which seemed to just fall off. I could see some oil there, so I will need to oil that bit.
- It doesn’t look like the gear/bearing on the automatic work is removable, since one side looks like it is riveted in place.
I spent the rest of the evening pegging all the jewel holes and wiping them down with some alcohol on a swab, and trying to address the bracelet. I managed to bend off the last hook link in the bracelet, so that it can attach to the clasp, but it ain’t pretty:
Fortunately, this will be hidden most of the time. I might still try and buff out the scratches on it. Another issue I addressed was to file off the burrs on the holes in the clasp, left over from the factory process that drilled them. They were preventing the links from being able to fully seat within the clasp. After filing, I sanded a bit with a 240 grit sanding stick, and it doesn’t look too bad:
After fiddling around more though, I’ve realized that because that hook link on the end doesn’t extend across the whole width of the band, it’s prone to popping out of the clasp. It’s not a huge deal, but I may end up using the hook link from the other band that I got, even though it doesn’t match as well.
Jun 14, 2026 7:41 PM
I spent the better part of today working on the watch. I used the ultrasonic to clean the case and bracelet, and then the movement. That didn’t take very long in total, maybe 45 minutes. However, I spent the next several hours addressing some of the issues with the case. I spent a long time sanding out the giant scratch in the case back. I used my pen-style sander to good effect, that thing is awesome.
I ended up taking out the brushing on the case back, and managed to add it back decently, with some effort. I tried holding the case back in my movement holder, and sliding it along a surface, but I ended up putting scratches outside the flat part. So, I jury-rigged a cutting head for a hand-held compass to cut a circle out of Kapton tape, and re-polished the banked sides.
I did an initial polish on the bracelet, and got started on polishing the case. There were some spots around the lugs that required a bit of extra work to take out some scratches. I am going to polish the whole case, and try and re-apply the brushing on the front face. It’s gonna be tricky, since it’s a circular brushing that follows the contour of the dial.
Side note: after asking on the forums, it seems I may be able to use a regular armored crystal, and just remove the tension ring. So, I ordered a few from Otto Frei, we’ll see if they work.
Jun 16, 2026 8:42 PM
Talk about fast delivery! I guess because I’m just across the bay from Otto Frei, it was always going to be fast. I actually ordered 3 crystals, one up and one down from the size I thought I needed, but the larger size was incorrect. No worries though, since the size I thought would work actually matched the dimensions perfectly!
No other updates, beyond finishing the polishing on the case. Here’s a picture of the polished case (never mind the stray polishing compound on it), and the armored crystal from Otto Frei:
I couldn’t quite get all the brushing out, but that’s OK since I’m going to re-apply it anyways. So, the next step for the case is to run it through the ultrasonic to remove the polishing compound, and then brush the parts that I want. I’ll brush the case, and also the outer links on the bracelet.
This is maybe the third case that I’ve worked on, and I find that I enjoy it more and more. It requires far less concentration than working on the movement, so it’s a much more “meditative” process, and I find I can relax a bit more.
Jun 21, 2026 3:48 PM
Perhaps I spoke too soon. Absolute disaster: I sanded through the plating on the case. Hard to tell from the picture, but I can clearly see the brass/copper coming through the plating right near the dial opening.
I am incredibly frustrated with myself, because I really should have known to stop trying with the brushing when it wasn’t working correctly. I’m not sure what I’m going to do now. I’ll ask on the forums for some advice.
Jun 22, 2026 7:25 PM
I got some opinions from the forum. I think the verdict is that to truly fix it, I’d need to completely sand it down, and re-plate it. But, I got one other interesting suggestion: sand and polish down just the front facet to the brass, which could give a cool two-tone effect. Given that a proper fix would be to sand down the whole thing anyways, I’m going to give it a try. I’ve ordered a watch case holder in order to better angle my sanding, so we’ll see how I do once it comes in. It’s possible I’ll also want to get some kind of jig or something, to keep the case at a consistent angle while sanding.
In better news, I managed to reassemble the train of wheels. Thankfully, I remembered that I suspected that the cap jewels for the balance had different thicknesses, and probably needed to go back in correctly. I managed to snap a pic that shows the difference:
You can clearly see the cap on the left is much, much thicker. I managed to oil both caps on the first try, and the train pretty much fell into place.
I really like the design of the internal bridge for the center wheel. I also noticed that the tolerances for the spacing between the wheels is incredibly tight: some of them are just barely far enough apart so that they don’t interfere with each other accidentally. I’m always amazed at the precision of these things.
Jun 27, 2026 3:53 PM
I recall that I re-installed the cap jewel for the escape wheel a few days ago, but I never mentioned it above. It is this one, which has a fixed shock setting, attached to the cap stone itself:
(This was before I cleaned it, obviously). Getting it back in was an absolute bear, since that setting makes it very difficult to hold. I ended up putting it upside down right next to the hole, and kind of sliding it and flipping it at the same time to get it to where it needed to be. The oil probably doesn’t look that great, but honestly I was just happy to get the dang thing back in, oil or no.
The case holder came in from eBay a couple of days ago, but I wanted to finish reassembling the movement, because I wanted a win on this watch. So today, I spent about an hour putting it back together, at least everything except the automatic rotor.
I managed to get it running pretty well, too:
I’m going to spend some time designing a jig to hold the case holding tool at a fixed angle, so that I can accurately sand off that front face of the case.
Jul 8, 2026 5:42 PM
I’ve been busy. I designed and built a case-holding jig, and I am quite pleased to say that I was able to very nicely sand down the plating on just the beveled face on the case:
To be honest, I am actually really surprised at how well it came out. I was half expecting this to not be salvageable, but I can definitely proceed now with the case looking like this. It’s actually kind of difficult to tell that the brushed face isn’t gold plated. Since the brushing is such a different texture, it kind of just looks like the same material as the rest of the case. I am 100% sure it will tarnish differently, but I’m hoping it will actually make it look even cooler.
Jul 18, 2026 11:04 AM
Success! I have finally completed this watch! The first thing I did today was try and case the watch. However, when I attempted to put the bezel in the armored crystal I bought, it appeared too loose. So, I ended up sticking two tiny pieces of tape on the inner lip of the crystal, which got the bezel fitting much more snugly:
Then, I got to work finishing casing it. I put the hour wheel and dial back on, and then successfully set the hands. Hand setting is always the most stressful part for me, but thankfully this movement was really well made and they went on just fine:
Then I went ahead and got the movement back in the case. Strangely, I had a lot of issues inserting the stem into the movement, but with some gentle finagling, I managed it eventually.
I am super happy with how well aligned I got everything! Then, I worked on getting the bracelet back on. Because it’s for my brother-in-law who has fairly slim wrists like me, I ended up taking out four links. I mistakenly took them out from the clasp side on one of the bracelet ends, so I ended up having to do a fair bit of back and forth. And here’s where we ended up!
Jul 21, 2026 5:56 PM
I am gifting this to my brother-in-law, who had a complicated relationship with his grandfather. I hope he likes it! Bon voyage Gruen, may you continue to tick for another 50 years!
Amateur Hour Watch Restoration 
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