At about the same time as the first generation Seiko 6105 divers watch first made its appearance in 1968, so did a rather more aristocratic sibling whose bragging rights exceeded those of the humble 6105 in a number of departments: where the 6105 was rated at 150m, the 6159-7001 countered with 300m; where the 6105 was fitted with a 17 jewel automatic 6105A running at 21600 bph, the 6159 could boast not only a much higher jewel count but considerably higher time-keeping precision by virtue of the fact that its movement ran at 36000 bph. Into the bargain, the 6159 also hacks and hand winds.

Those of you thinking I might have auctioned off my children to aid the acquisition of a 6159-7001 are sadly mistaken. Instead, I’ve come up with a strategy to inject a bit of the blue blood from that 6159 into our blue collar diver’s watch, the 6105-8000.

I should preface this account by making the observation that my inclination to scratch the modder’s itch has receded somewhat in the past year or two and when the urge does surface, it is usually as a result of circumstances showing the way. Most recently, for example, what constitute modified watches emerging from this here gaff include a 6218 Seikomatic with a dial/case mismatch and a 62MAS hot-rodded with a high jewel count movement. The former was motivated by the need to substitute a hopelessly past it gold-plated case and the latter by the availability of a spare 39 jewel 395 and an idle pair of hands (doing the devil’s work, some might suggest).

This latest diversion was motivated by the accidental bargain basement acquisition of a 61GS as a source of spare parts. Having acquired it however, the germ of an idea started to form. The high beat 6146 fitted to my scrap yard special is, in essence, a high octane 6105, and a close kin to the largely identical 6159 fitted to that out of reach 6159-7001.

So, the plan would appear simple (and cunning, of course): remove the 6146 movement from the Grand Seiko pictured above; service it; make any adjustments as required and transplant it into a handy 6105 recipient. The extent to which we can exploit all that the 6146 has to offer necessarily favours the choice of the 6105-8000 over the later 6105-8110. The locking crown on the latter for example would immediately scupper any notion of hand winding, although that feature could be accommodated with a triplock conversion. There is one other issue which I had not anticipated upon starting the project and with which I am still grappling as I start to write this entry. We’ll get to that though in due course.

So, we’ve met the donor, what about the recipient? Well, that has a bit of history behind it. It started as a 1969 Seiko 6105-8000 with an excellent case and bezel. The dial markers though were quite badly corroded and a few years ago I had it professionally relumed. This is how is looked 6 years ago (artfully photographed to disguise the ropey state of the dial).

In my search over the years for increasingly better dials for my 6105’s, the dial pictured above ended up being transplanted into another watch (a hand-me-down of sorts) and this watch subsequently ended up with the dial I relumed a year or two back and documented here. The long and short of it is that our candidate has already experienced a degree of movement/dial musical chairs and so another iteration isn’t going to do it too much harm. We’ll set this to one side for the moment and concentrate on seeing what potential the 6146 has to offer.

As with my last 61GS featured here, the 6146-8000 you see above was not interested at all in actually running. But unlike the 6145-8050, the problem in this case was not a broken mainspring but something else. I could wind in power, and the balance wheel would lethargically offer a couple of harmonic cycles in response to a hopeful prod from a bit of spare pegwood, but run it would not. We’d need to delve deeper to discover why but for the moment let’s take in the slightly grim sight of the grubby movement in all its soiled glory. The most obvious visual issue is that the winding rotor is incorrect, this one having been sourced at some point in the past from a 6106A.

The state of the case, dial and hands is irrelevant to this exercise and so let’s get the movement out and start the usual process of rendering it into its constituent parts. The calendar side reveals the first component surplus to requirements:

A day wheel. In removing that, I also plan to replace the day and date driving wheel with a date-only driving wheel and the date dial guard with one from a spare 6105A.

As this movement was designed to be fitted to cases with the crown at 3, the date ring will need replacing too. A quick appraisal of the balance side of the movement reveals not much more than some odd bluing of the ratchet wheel and regulator but it otherwise looks sound.

Pausing briefly to note the sealed mainspring barrel, the state of the centre wheel bridge jewel catches my eye but we’ll return to that shortly.

Back to the calendar side, and we encounter our first fly in the ointment.

The tip of the setting lever spring is broken which means that any grip the lever might have when the crown is set to the time setting position would be tenuous at best. Fortunately, this component is the same as that used in the 6105 and I have a spare. Let’s return to that rum-looking centre wheel bridge jewel.

It is clearly on the verge of disintegrating: I wonder if this is why the movement refused to run? My recent decision to acquire a Seitz jeweling tool seems particularly perspicacious, having had cause to draw on its services twice in as many months. Extraction of the jewel in this case proves a great deal easier than with the 8305 described a couple of posts back but the state of the extracted jewel reveals that the only things holding it together were the hole in the bridge and the centre wheel pinion.

A replacement is sourced from a defunct 6119 and in a jiffy, we are back in business.

With the two obvious problems identified and fixed, we are ready to clean and rebuild the movement. As with the 6145 project described a couple of months back, I’ve elected to perform a substitution of the barrel and mainspring with a donor barrel and arbor from a 6139 and a new mainspring from Generale Ressorts (in spite of the fact that the original mainspring appears to still be functional in this case).

The balance side rebuild proceeds without a hitch.

The next item of business is to convert this day/date movement into a date-only movement. This straightforwardly involves substituting the date and day driving wheel of the 6146 with a date driving wheel from a spare 6105A.

The placement of the printed numerals on the original date ring assumes the movement is fitted to a dial designed for a case with the crown at the 3 o’clock position but the diver has its crown at 4 and so we need to find a suitably configured substitute. The best date ring I have that will work is harvested from a 6309.

And finally, we replace the 6146 date dial guard, complete with its redundant day jumper, with a dial guard from a 6105.

Notice the absence of a tapped hole in the main plate to accommodate the fourth fixing screw, just between the 11 and 12 on the date dial. A minor aesthetic blemish that I can live with because it saves me the trouble and expense of sourcing the correct 6145 part and in any case, it will be hidden as soon as the dial is fitted.

With the service complete, a quick timing check reveals that the movement is running flat with zero beat error and very good amplitude so I leave it to run in for a bit and turn my attention to what I had anticipated would be a smooth run to the completion of the project.

Those of you who recall my 6105 dial relume a couple of years back may remember that the SEIKO logo on that dial was tarnished and my solution at the time was to rub the blackened plating back to the brass.

In my infinite wisdom, I thought that a movement upgrade deserved a better logo and so in a fit of slightly manic fervor, I set about removing the old logo with the aim of fitting one salvaged from a spare dial from a SNZ55: a fine idea as a concept; a complete nightmare in the execution.

The logo fitted to the SNZ dial popped off easily enough with a bit of careful, iterative encouragement with the head of a pin from the rear. No such luck with my 6105 dial. I had to grind out a pair of dished intents at the rear to make any progress to unseat the pins and it was only after a good couple of hours that I finally managed to extract the old logo. In doing so I’d created a small peaked dome to the front in the region of the left hand hole and had to work it flat again with a bit of pegwood.

In the end, the damage was not really too significant but this episode will definitely be filed away in my back catalogue of narrowly averted disasters. Those of you contemplating this with an old dial of any value at all should proceed with extreme caution (or better still, bin the idea at conception).

Having removed the old logo, affixing the replacement naturally requires the two posts to the rear of the logo to align with the holes in the dial. I actually tried several potential donor logos, some of which I rejected on grounds of condition and others because the pins were either just too far apart or too close together.   I ended up settling on the SNZ55 logo partly because it was in perfect condition, partly because its matt finish was a much better match to the original finishing of the correct 6105 logo, but most importantly because its pins lined up almost perfectly. I very carefully pressed it into place and then secured it with a couple of dots of GS hypo cement from the rear.

The next job, rather than an ill-judged flight of fancy, is a necessity born from the requirement for the stem to operate correctly with a clutch wheel and winding pinion rather than just the clutch in the case of the 6105. The 6146 stem looks superficially very similar to the 6105 stem but there are noticeable differences in the dimensions when you look closely.

Replacing the stem is straightforward, other than the need to take care to trim the new stem to the correct length. At the first iteration, we see the stem is still a little long.

A little more off the length and it is just about perfect. Refitting the hands proved slightly problematic in that the seconds hand was loose on the fourth wheel post and I had to tighten the tube with a pin vice before it would seat securely. I am not completely sure whether this is because the post of the 6146 fourth wheel has a smaller diameter or that the tube on my seconds hand had enlarged with repeated refittings. I suspect the former.

The movement is now ready for the case and we can see that from the dial side of the watch, there is nothing to give away the changed configuration beneath (but see later on to what extent this is true from the rear).

The lume in the pip on the bezel insert had noticeably degraded over the course of the 5 or 6 years since its visit to a relumer in Spain and so I took the opportunity to freshen it up.

So near and, as it turns out, still a little way away from a satisfactory completion. The autowinding mechanism slots happily enough into place.

I have to say, it all looks rather splendid and I am feeling quite pleased with myself. Not for long though. The problem with these 36000 bph movements is that they require a thicker mainspring capable of generating decent amplitude. A thicker mainspring requires greater torque when winding. No problem if you are winding by hand but if you rely on the autowinder, as you might reasonably expect in an automatic watch, then the winding weight must be heavy enough to overcome the resistance offered by the mainspring. The winding weight that came with the donor Grand Seiko was incorrect, having been sourced at a previous service from a 6106A. It fits but is not heavy enough to pivot about its axis under its own weight. Fortunately, a want-to-by posted on a watch forum secured the correct part and with it in hand we can see just how different the two weights are.

One problem solved and another created. In fitting a rotor of the correct weight to allow it to perform its function, we now have a movement that sits too high in the case and there is consequently no longer sufficient clearance to allow the case back to be tightened down correctly.

I am going to confess that I was only alerted to the problem when I noticed how quiet the auto-winding mechanism appeared to be. It was quiet, not because of its silky smooth operation but because the rotor wasn’t turning, and it wasn’t turning because the inner surface of the case back was holding it fast. The original case back simply will not work with this movement.

I have been through several permutations trying to come up with a solution, wasting time and a little money in the process and have not yet arrived at a wholly satisfactory solution. The only case back that I have that fits the case properly and has sufficient internal clearance to permit unimpeded rotation of the winding weight is a spare from a 7548-7000.

These are a fair bit deeper than the standard 6309 case back to allow clearance for the battery in the 7548. I have also experimented with a display back from a 7S26 Seiko 5 watch but while it fitted the case, it was not quite deep enough to clear the rotor when screwed fully in.  So for the moment, I am going to make do with the 7548 case back and look into alternative solutions over the next few weeks. I’ll report back with any developments.

Of course, when the watch is being worn, the appearance from the rear is neither here nor there. It is the view from the front that’s important and so let’s conclude with a selection of the usual glamour shots, showing the (more or less) completed watch in its best light.

The only clue from the front that this watch contains a movement harvested from a high beat 61GS is in the way the seconds hand makes its way around the dial.  See if you can discern the difference: