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Time instruments

This is an article I wrote last year about a restauration of my Seiko 6105 diver watch. Unfortunately my account in the forum I wrote it for got locked over a trifling issue (although the forum in question prides itself on non-oppressive moderation), so I’m having my article again. It is a bit rough round the edges, being re-posted here verbatim, at least until I find time to give it a once-over.

I have reported a couple of weeks ago that I finally got hold of a Seiko 6105. Just what I wanted, all original parts, but with problems that I had to fix. I have fixed the most severe now and she’s in working order. So here’s a bit of a report and some pictures to look at.

I won’t assume you all saw my initial post, so a reminder, this is how I got it:

There is the black slime on the lume particular to Seikos from this period. Weird stuff, seems to grow out and spread across the neighbouring regions. It is corrosive as well, there are marks on the stainless steel hands beneath it. It seems to do this to the chromed indices as well, but to a lesser extent. The bezel insert is a bit scratched, so is the case, but they are in surprisingly good nick when you compare them to the crystal, which is terribly scratched. You can also see that the crystal looks a bit milky – this I found out to be dirt on the inside of the crystal, probably caused by some compound inside decaying and gassing out the stuff that then settled on the crystal. I suspect the lume. But the biggest problem was that it was a non-runner. I was not deceived, I bought it on the SC, the seller let me know exactly what I was buying, and that was exactly and precisely what I got (thanks again David). It was working, but the timing was way off and it kept stopping. So:

Just to see how bad it is:

Well, ra-ther. Both the timing and the beat were horribly out of whack. Well, that was the least of its problems for now, as it was about to be serviced anyway. By me. So on to the disassembly, here’s the date wheel off:

What strikes me with Seikos of this vintage is how well made they look. I don’t have any experience to speak of, but the hour wheel is very nicely machined, there is no friction washer on it – seems like they were so confident in their machining that they thought it unnecessary. Indeed, there is hardly any play in it. Towards seven-ish from the centre you can see the shock protection (diashock), and next to it is a big gaping hole in the base plate. I only figured out what that is for while looking through pictures for this post. It’s to open the regulator pins so you can separate the balance from the balance cock. I did that the hard way. Between the hour wheel and the Diashock there is the reduction gearing and the wheel for the date change mechanism. That one struck me as a bit needlessly complicated. On the wheel there is a spring-loaded finger, the other end of which runs on the eccentrically mounted cam/washer/screw thing:

The purpose of that is to allow the finger to extend when it needs to mesh with the date wheel teeth, and to retract when pointing toward the centre. Which is nice – except that I can’t see what it would interfere with if it did not retract. They were probably just too smart to make it simple.

With that out of the way (I like to remove the vulnerable bits on the dial side first so I don’t have to worry about scratching something vulnerable and visible while putting it in the movement holder) I could start on the time bits.


The balance is out already. That is the next vulnerable bit that I absolutely want to have out of the way as soon as possible. Then I had a look around it. It was quite pleasing. No scratches or marks, bit of wear on the corner of the plates where the rotor would strike them when you bump it. Predictable dirt. But underneath all that a nice healthy looking movement. I could only hope it would look like that all the way through.


It did. I would not be the first to eulogise over Seiko’s magic finger auto winding system, but you can’t pass on it either. Just look at that auto bridge – that’s all there is to it. An eccentric pin moving the magic finger pawls around, the wheel they’re pulling on, the gear on that one rotates the winding wheel – job done. Effectively 3 simple parts resulting in a bi-directional highly effective winding system – that’s pure genius. Now I’m not sure if they actually invented that. IWC uses a “pellaton” winding system quite similar to this, except that it has a heart-shaped cam in the centre instead of the eccentric pin. I don’t know who came up with it first, but I dare say Seiko’s is better – simpler, less surfaces to lubricate, less wear, less to go wrong. IWC’s should be a bit more efficient, irrelevantly.

Below the auto bridge there is a bit of predictable dirt. It either was severely overoiled at some point, or the lubricants from the auto bridge have seeped down, you can see an oil stain surrounding the central jewel. The mainspring barrel pivot jewel is ruby, but it looks black because it is so dirty. Interestingly, despite jewels being generously strewn over the movement, the reduction wheel pivot is metal. Wonder what that’s all about.

Central plate off. Still looking good.

The central second and reduction wheel out. The gold coloured bit is the wonderfully simple hacking lever. When you pull out the crown to set the time, the stem barrel drops down onto the gear below so you can move the hands around, at the same time the lever is pulled along, contacts and stops the balance. Watch hacked.

Not much of interest beyond that. So just the final shot: the broken watch.


Of course, there’s also the most important bit – the balance assembly. I have identified the reason for the watch stopping in the hairspring being dirty. There was a big drop of liquid between the regulator pins, obviously on the hairspring as well. Before I disassembled it I had it for quite some time on the timing machine, trying to provoke it to stop again, different positions, shaking, little shocks. When I finally managed it, there was a faint ringing noise as the amplitude fell rapidly to a standstill, the indication that the hairspring is touching or catching on something. It was stuck on itself, two of the coils on the extremely tightly wound spring were held together by a tiny droplet of liquid. Usually I’d prefer not to separate the balance from the balance cock, it is incredibly fiddly and touchy work, screw that up and you’re in a world of hurt. However it was needed. I rinsed the balance several times in some benzene or naphtha (lighter fuel), then in alcohol. I’m not sure I managed to clean it as thoroughly as I should, after I rebuilt it it stopped once again. It was suggested to me that the hairspring may also be magnetised, so that is the working theory for now. Before I attack it with more aggressive solvents I’ll give that a shot. At the moment however it is working, so the problem might have gone away.

Putting it back together was quite uneventful. Straightforward thorough cleaning, inspection, oiling, more checks… I seem to be getting better at that, I’m glad to say, I managed to clean and oil the shock protection in one go, without dropping or losing anything once. I seem to be getting sloppier as well, I put a bit more oil in the pivots than I intended, but it should not be too much.

This is getting a bit longer than I expected, so I’ll split it up now. I’ll continue in the followup to this, stay tuned if you’re still awake.
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