Natural selection: A Seiko 6306-7001 from 1979


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In 10 short years between 1965 and 1975, Seiko had somehow managed to conceive, design and produce three generations of classic ISO-certified 150 m divers’ watches: the first, the 62MAS, was produced between 1965 and 1968 and was a clear statement of intent both in the integrity of its engineering and the originality of its design. The follow-up was the first generation 6105-8000/1, produced from 1968 to 1970, a larger 42 mm watch whose only shared components with the 62MAS were its substantial crown and the hour/minute hands. Both watches used a freely rotating friction bezel but where the 62MAS used an armoured acrylic crystal, the 6105 used a double-domed tempered mineral glass seated in a complex profile rubber gasket. The exposed 3 o’clock crown in the 62MAS had also moved into a partially guarded 4 o’clock position in the 6105. That first 6105 morphed into the asymmetric cushion cased second generation 6105, the 6105-8110/9, produced between 1970 and about 1977 and whose improvements included a 60-click indexed bidirectional bezel turning ring and a locking crown. For some reason, the two 6105 models are routinely categorised as essentially the same generation, but to my mind, they are really quite different watches and should be regarded as distinct from one another, in spite of the fact that they share common movements, dials and hands.

Officially, the 6105 disappeared from domestic Seiko catalogues in 1976 but the model continued to be produced until 1977 or maybe even as late as 1978. With a notional 5 year production span under its belt for the second-gen 6105, in 1975, Seiko charged a young engineer, Ikuo Tokunaga, with the job of designing a replacement. Tokunaga’s new more rounded cushion case design would incorporate many of the features of the older watch, such as the sprung ball-bearing 60 click bi-directional bezel and case construction philosophy, but with a screw-down crown replacing the locking crown design of the out-going watch.

Out too with the embossed dial and coin edge bezel turning ring, replaced with a printed dial and a new, deeper, grippier turning ring. The double-domed Hardlex crystal of the 6105 was also dropped in favour of a beveled flat Hardlex. The lifetime of the 6105B movement had also run its course and the new watch would feature a brand new 21600 bph movement, the 6309A featuring both date and day complications. All in all then, quite a departure from the older watch with one or two aspects of the design hinting at cost-cutting. Nevertheless, this new watch, in common with the three that preceded it has come to be viewed as an absolute classic and wholly original design.

The new watch was conceived at the outset in two slightly different specifications, one for the domestic Japanese market and the other for overseas. Where the overseas version would be fitted with the 17 jewel 6309A fitted with bilingual day wheels appropriate for the target market, the Japan domestic version was to be fitted with the higher specification 21 jewel 6306A that added seconds hacking and which was fitted with English/Kanji day wheel. The 6306-7000/1 made its first appearance in the 1976 edition of the domestic Seiko Catalogue, with the 6309-7040 absent but presumably featuring in catalogues produced for overseas markets.

The received wisdom, which originates from a contribution from Tokunaga himself on a watch forum in 2003 (see here), is that the 6306 went into production slightly in advance of the 6309 but with both models produced from 1976. However, I’ve not seen any examples of 6309-7040/9 with 1976 serial numbers and so it may be that the first 6 to 12 months of production was dedicated to the JDM 6306-7000 with 6309-7040/9 production kicking in from early 1977.

I’ve written on a number occasions about the 6309-7040 (see here, here and here for example), but the present post concerns the JDM sibling, the 6306-7001, a model that has up to this point eluded me (or perhaps I’ve just eluded it). So we find ourselves breaking new ground but also in a sense in very familiar territory. The example shown below dates from May 1979, a little over half way through the production lifetime of this much rarer partner to the 6309.

Face on, this watch makes a pretty decent impression, barring the obvious encroachment of funk on the hour hand. It is clearly wholly original, the bezel insert is in very good condition and the dial looks perfect. The case back is clean and free from the commonly encountered signs of case back opener slippage.

The reason I think that I was able to secure this one without breaking the bank is that the mid case sides have come in for some abuse during the watch’s life. In particular, there is quite a nasty dink to the case edge on the left hand side that has created a small rise to the upper surface where the metal has compressed.

The crown side is better but also worse; no major dents but a criss-crossing of battle scars to mark the passing of time and the fact that this is a watch that has seen some use.

It is therefore somewhat remarkable that the rest of it, particularly the bezel insert, should be in such good condition. The case back was secured sufficiently securely to defeat my attempts to open it by hand and so I brought out the big gun to do the job.

It is common practice for watchmakers to inscribe or otherwise mark the inside of a case back with the date of the most recent service but in this case we encounter the initially inscrutable set of figures 57.6.28SN which to the Western eye reveals little in the way of useful intelligence, other perhaps than that the 6.28 may indicate the 28th of June. However, this being a Japanese domestic model bought and used in Japan, we must remember that the Japanese commonly still use their traditional calendar that references years in terms of passage through a particular imperial era. This watch was made in 1979, which translates to year 54 of the Shōwa era, the period of the reign of Emperor Hirohito. We might therefore interpret the first figure in the case back marking as Shōwa 57, which corresponds to 1982. Three years seems a rather short period between purchase and first service but perhaps this watch needed a repair or some other unscheduled intervention of a watchmaker at this relatively early point in its life.

I can find no other markings on the inner case back and so 1982 was either the last time this watch was serviced or subsequent services have not been recorded. A closer look at the movement in situ, with the winding weight removed suggests that the former may be closer to the truth, the movement refreshingly free from signs of damage that come from repeated de- and re-constructions by less than fastidious watchmakers.

Before liberating the movement from the case, I removed the autowinding mechanism to allow me to wind in some power before taking a pre-service measure of how the movement is performing.

This pair of photos reveals two notable features of the 6306A. Firstly, on the left, we see that the train wheel bridge is fully jeweled, with both the escape wheel and third wheel benefiting from Diafix settings and the fourth wheel from a single jeweled bearing. The 6309 by contrast uses just a single jeweled bearing for the escape wheel, and steel bearings elsewhere. To the right, we see how the design philosophy of the 63 series movements is deviating from the preceding 61 series: the autowinding mechanism makes use of a push-fit plastic retaining plate to hold the pawl lever in position where in the earlier 6105 a screw-fixed metal plate would have been used. To give Seiko the benefit of the doubt, I favour the view that this difference is aimed more at convenience of assembly and ease of service rather than just plain old cost cutting. In terms of engineering integrity, the proof of the pudding of those design decisions is born out by the fact that these parts are still happily performing their duty 39 years later.

With a full wind, the timing machine reveals that this watch is badly in need of a service: -45 s/d, a miserable amplitude of 143 degrees and a substantial beat error of 1 ms.

On the upside, the timing lines are noiseless which suggests that there are no fundamental issues to deal with other than dirt and dried lubrication. Time to get the movement out of the case and set the hands for removal.

The hour hand lume is largely free from discolouration but the same cannot be said of the minute hand, whose degradation means that it will be retired from service when the movement comes back together later on. The dial itself is essentially perfect, as good an example as I have ever seen, with nicely honeyed, even lume on the hour markers.

The imprinted 94 numeral on the rear of the dial suggests a manufacture date of April 1979, one month prior to the date indicated by the serial number on the case back. We’ve met 63 series movements on numerous occasions in the past, and so I’ll simply illustrate in snapshots the disassembly of the movement to highlight particular features. On the calendar side, for example, we note the English/Kanji day wheel fitted to this Japan market watch, and the dulling of all of the plating on the metal surfaces as a result of the long passage of time that has passed since the last service.

The grime is equally evident on the train side of the movement. In removing the Diafix cap jewels, I noticed that the springs were unmarked and undistorted, suggesting perhaps that they had not previously been removed.

It is worth noting one other significant feature of this movement compared to the lesser 6309: the presence of a hacking lever that performs its duty by operating directly on the balance wheel.

The final order of play before cleaning commences is to remove the molybdenum grease-encrusted mainspring.

Into reverse, and we can start the process of piecing our jigsaw back together. I’ll skip through the assembly of the train side, but will pause to note: the freshly cleaned mainspring, barrel and arbor; the need to remember to reinstall the hacking lever before fitting the wheel train; the satisfaction that comes with a neat re-installation and lubrication of the two Diafix settings; and the miracle as the movement springs into life once more.

With the movement running, let’s take a measure of the extent to which it has responded to the attention being lavished upon it. The timegrapher reveals that, contrary to my suspicion in the past that the 63 series movements are not entirely to be trusted to deliver, this one seems rather pleased with itself.

0 s/d, 249 degrees amplitude, 0.0 ms beat error. And not a single movement part replaced. This does make me wonder whether this movement has seen much use at all since that 1982 service, in which case the external wear must have been inflicted in the first three years of its life.  Maybe that dink was the result of an incident that prompted the unscheduled service visit.

The calendar reconstruction proved uneventful and so we arrive at the point of having fitted the dial and needing to think what to do about the hands.

I think perhaps we can postpone that decision and instead turn our attention to the case.

Removing the bezel turning ring sometimes carries with it the potential hazard of losing the sprung ball bearing that provides the click for the bezel. This can happen when the ball bearing has broken free from the crimping of the hole that ensures its capture when the watch was originally made. I raise this point because needless to say, the click ball had done precisely that and in an absent-minded moment, I allowed it to escape.

I am nothing if not methodical and in retracing my steps, I fortunately located the errant ball, my search aided somewhat by the fact that the ball was lightly coated in a smear of dirty grease and had stuck to a surface rather than rolling free. All of the case parts except the turning ring find their way into the ultrasonic bath, the case, crystal retaining ring and case back having first benefited from some manual cleaning first with pegwood. Once dry, we are poised ready to reassemble the case.

From the moment I clapped eyes on the watch, I have been debating with myself what to do about the scarred and dinged case sides. At the time the photo above was taken, I had resolved to leave it alone, to allow the watch’s past experiences to remain on display. My reticence to attempt to smooth away the battle scars was fed in part by my general alignment with the principle that any case work somehow diminishes the integrity of the watch but also by the worry that I might make a bit of a Horlicks of the process. All of that having been said, without any conscious change of mind, I found myself carried into action, having surveyed one time too many the dink-induced lump on the upper surface of the left hand side of the case. I started by working that raised lump with some wet and dry sand paper and once satisfied that I’d smoothed it away turned my attention to the case sides. The shape of the cushion case really does help to minimise the potential hazard of spoiling the sharp lines as long as you allow your hands to cushion your action and so I beavered away, working my way from the coarser to finer grades of paper before working up a polish with graded finishing paper. I like this approach because the end result is a polish that achieves a patinated appearance that complements the condition of the rest of the case.

In taking this approach, you need to strike a balance between achieving a satisfactory finish and eradicating every flaw. In this particular case, to have attempted the latter would have compromised the lines of the case too much and so one or two remnants of the damage remain to act as ghostly keepsakes of its history.

Next, let’s have a crack at the crown. In order to properly clean of the groove in which the crown gasket sits, you really do need to remove the stem, a process aided by a quick exposure of the crown to one of the gas burners on our hob.

A forensic clean of the innards, and we can introduce a fresh crown gasket before refitting the stem, secured in place by a dab of Loctite.

With that done, the reconstruction of the two part sprung stem can follow.

The movement is still awaiting its auto-winding mechanism and so let’s fit that next. The technical manual advises that the transmission wheel should first be set onto the train wheel bridge and so that is what we do next.

The automatic framework is then placed into position but the teeth of the pawl lever will not at this point be engaged with the transmission wheel.

Engagement is achieved simply by opening the pawl slightly with a pair of tweezers, which allows the tips to find purchase on the edge of the wheel. With that done, the framework can be tightened down.

What follows is a bit of a wild goose chase triggered by my uncertainty about what to do with the hands. The position I found myself at this point is not unfamiliar and I like to think that I learn from my historic misjudgements but in much the same way that a somewhat dim-witted dog finds its way thwarted through an aperture by a stick in its jaws until it figures out it needs first to turn its head to one side, so I find myself following a path that leads if not to obstruction then to inevitable dissatisfaction before resolution.

With the original hand set excluded from consideration, we can contemplate either: a) reluming the original hands or b) replacing the hands with something in an aesthetic state in better keeping with the rest of the watch. I quickly discount the reluming option, in part because I’d rather keep the original hands as a momento but also because it doesn’t seem the right course of action for this watch. With reluming discounted, we are faced with replacement. I have two options in my parts stash.

To the left, we have an OEM set of Seiko hands whose lume is still very much alive and kicking; to the far right, a set that I believe may be old OEM replacement stock whose lume is exhausted. The set in the middle is the outgoing original set. Some of you may recall that we considered both right- and left-most sets when restoring the 6309-7040 described in a previous post (or two) and I discount the right set for the same reasons I did then (a powdery quality to the lume). That leaves us with the relatively fresh set of Seiko hands complete with active lume as the only remaining option.

The colour match is actually very good, certainly within the range of what appears authentic when surveying original hand/dial combinations on 6309/6306 divers from this era. With that decision seemingly made, we can assemble the case.

For the crystal, I eventually opted for a coated flat sapphire after a wrong turn or two involving an ill-fitting crystal gasket. Ideally, I would have bought a tempered mineral replacement but the customs charges from the US supplier are just too large to make such a purchase economically justifiable unless buying in bulk and in the end, I am very pleased with how the sapphire looks.

With the case ready and the movement complete, it is time to case up.

In with a fresh gasket, fit the case back and we can prepare to refit the turning ring.

The only minor inconvenience in this final part of the puzzle was to place the errant click ball into position before refitting the turning ring, complete with a fresh bezel gasket. This does not quite bring us to the end of this story and to explain why, we need to survey what we have at this point, paying particular attention to the impact on the package as a whole of our choice of handset.

I know there will be some of you out there shouting at your screens ‘it’s fine’, ‘you are nuts’, ‘get a grip’, ‘see a shrink’. But for me, with the hands in place, in the context of that beautiful dial, it is clear that I have made a misstep. For starters, it is simply wrong to fit a set of hands with active lume to a dial whose lume is exhausted. Secondly, the hands themselves are too rounded, too shiny and, even though they are Seiko originals, just a bit cheap looking. I need to find another option that will do this watch proper justice.

By a stroke of foresight on my part, I just happen to have a rather decent example of a Seiko 7548-7000 with a perfect set of contemporary flat style Seiko hands. They are period correct, the lume is of an authentic shade and it is dead. The plating is a little tarnished but that is easily sorted with Rodico and some gentle work with lighter fluid-soaked kitchen roll. Out comes the movement, off with the rejected replacement hands, and on with the hour/minute hands from the 7548 donor (don’t fret, I’ll figure out an option to replace its hands when, in due course, I get around to its service). Finally, I am happy that we have a handset to do the watch justice and which does not tilt the universe off-axis by emitting photons when it has no good business doing so.

The finishing touch is a vanilla scented Bonetto Cinturini Italian rubber strap of the correct period style.

Every time I find myself owning any watch with 22mm lugs and with a girth larger than about 40 mm, my equilibrium is perturbed and I know that sooner or later, it and I will part company. The truth of that statement is evidenced by the fact that the only watch that fits that description that I own and is fit to wear is the one described in this entry. I have always liked this generation of Seiko 150m diver but perhaps more as a matter of principle than of practicality with the result that inevitably I find myself gravitating back to the first gen 6105 and the 62MAS when the urge strikes to wear a divers watch. I think though that the exception to the rule may have presented itself here.

The Seiko 6306-7000/1 and 6309-7040/9 siblings are in my view the last of the great Seiko recreational automatic divers watches. The contemporary quartz 7548 holds its head high in this company but everything that has followed since has failed to achieve the same heights of originality combined with reflective evolutionary development that followed the path from 62MAS to 6306/9. The second generation 6309 that followed in the mid-1980’s feels compromised and cheap by comparison and further cost-cutting lead to the singularly undesirable 7002 series that preceded the SKX line. The evolution of the species in this case withered as production of the classic 6309 was outsourced to Hong Kong production before settling into the stagnation that followed in the subsequent 150m and 200m diver progeny. That feels like a rather downbeat note on which to finish but rest assured my spirit is lifted by the rather splendid 6306-7001 sitting on my wrist as a type these concluding words.