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This next project concerns what I believe to be the last real classic Seiko mid-tier divers watch, the Seiko 6309-7040, produced from 1976 to about 1987.  I’ve covered this watch before in the blog but not in the sort of nitty gritty detail I’d like to do here. I also thought I’d try a different approach with this one, presenting the process more or less in real time (this is a blog after all) and to use that more measured approach to highlight some of the features and potential pitfalls to look out for if contemplating the purchase of a 6309-7040.

The key then is to find something as original as possible; a bit of grot and patina are fine, welcome even, but above all I would suggest not going for anything which has been ‘got at’.   In other words, try to avoid watches riddled with aftermarket parts, fake Scubapro aspirations, and shiny, over finished exteriors disguising goodness knows what beneath.  The starting point to this project was completely unintentional, triggered by an interesting eBay auction from a UK seller, advertising a Seiko Scuba 150M. The key to my interest in this auction was that it was accompanied by just two small photos, little in the way of description, and importantly no references to the model number


The sparse description meant that the auction failed to attract as much attention as it might otherwise have done and my modest snipe in the end was sufficient to win the day.  Here’s a quick snap taken on my phone shortly after receiving the watch:


The watch certainly bears a few minor scars and scrapes and the hands in particular betray the fact the water has made its way in at some point. You can also just about see this in the photo that there are also some dried opaque globules spattered over the dial, possibly dried spots of saline from sea water ingress. However, the good news is that the watch is clearly 100% original and in good enough condition to make the basis of a good, honest restoration without recourse to third party parts suppliers (other, perhaps than a fresh crystal).

With the watch back home, a proper appraisal of its condition requires separation into its key components

Seiko 6309-7040 case components

From the left, we have the turning ring complete with original insert, the characteristic dished aspect to the insert and grained finish confirming it as pukka. Then the case, which again is really in very decent condition, a few nibbles at the sharper edges to the sides, but that’s actually ok with me. I like a bit of history on display. The ring to the right of the case is the crystal retaining ring, then the movement, dial and hands and finally the case ring, which holds the movement in place against the case back.

A closer shot of the case and case back shows the important presence of the click ball, vital to the operation of the 60 click bi-directional bezel. The completely unmarked case back suggests little in the way of a service history and inside I can find only one inscription indicating just a single service since July 1981 when it rolled off the production line.

Seiko 6309-7040 mid case

Looking next at the dial there is no doubt at all that first impressions were spot on.  With most of the salt droplets cleaned off with Rodico we see that the dial is in very good condition, printing crisp, the orange ‘WATER’ and ‘RESIST’ a tad faded but the bevel around the day/date aperture present and correct. The aftermarket dials produced by the thousand still fail to reproduce this key identifying feature of the original Suwa dial (although there are some sellers selling worked over watches featuring re-printed original dials – a strategy one might view as either better or worse, depending on your point of view).

6309 dial and crown

The Suwa symbol visible beneath the ‘150m’ signifies that the watch was produced at the Suwa factory in Nagano in Japan and was present on watches produced from 1976 to late 1981 when production, or at least assembly, was shifted to Singapore and Hong Kong.

So, that’s where I’ll leave it for the moment. My shopping list is relatively short: new gaskets, a replacement crystal and I think the hands are probably beyond rescue and so I shall do my best to find a set of original hands to replace them (in fact I’ve already gone some way to sorting most of the bits I’ll need).

4th December Update

Hands:  Arguably the most conspicuous component needing replacing is the hands, the corrosion and mold seemingly having run somewhat out of control. However, before considering my options about what to replace them with, I thought I’d have a go at cleaning them up: first a soak in acetone to soften the lume, followed by removal of the lume and as much of the tarnishing and mold-overspill as possible. I then gave them a careful polish with cape cod fluid soaked into a lens tissue and wrapped around a pair of tweezers.

cleaning hands

I have to say I was pleasantly surprised at how they turned out but the right most image suggests they still need one more go to get them to the point where I can contemplate a relume.  The hands at this stage had moved from ‘write off’ to contenders.  However, it is all too often the case that judging the point at which to stop can be tricky and unfortunately, I suspect I might have made a slight misjudgement here.  A final once-over with the cape cod and a clean and rinse in watchmaker’s cleaning solutions bring us a gnat’s whisker past the point at which I should have left them alone:

6309 hands too clean v2

I suspect the corrosion had probably compromised the plating and that final cleaning iteration was sufficient to reveal in places the brass beneath.  It may yet still be possible to use these hands but I think that decision will have to wait until the watch is otherwise complete.  In the meantime, the fall-back position is to choose from one of three sets of hands, two of which (sets 1 and 3) I’ve had for some time, and one of which (set 2, centre) recently purchased:

6309 hands selection

The right-most set are flat style aftermarket hands bought on eBay a few years ago and which I subsequently tinted for a project but never used. The finish on this set is pretty good but the lume hopeless and for this project I’d rather steer clear of aftermarket hands which places them out of contention. I am virtually certain the first set are authentic original hands; the luminosity is excellent, far, far better than anything you’d see on aftermarket hands and so these move into pole position.  The set in the middle are flat enough to be authentic, have the same gentle downwards curve to the hour hand centre hole as the first set and the lume has a granularity about it which makes me think they are indeed an old set of authentic service hands which have aged, having been out of their original packaging. The finish on this set though is a bit on the rough side, and the luminosity all but undetectable so they’ll be the fall back if for some reason set 1 falls out of favour.

Given the decent state of the original seconds hand, I could still reuse that but if I use the NOS hour/minute handset then they probably deserve something similarly blemish free

6309 seconds hand

We’ll catch up again in a day or two with a consideration of the dial before starting to strip and appraise the movement.

5th December

Dial:  The July 1981 production date for this watch places it towards the end of the run of Suwa-produced examples of this model.  At about this time, the dials fitted to these later Suwa watches featured a less pronounced bevel on the day/date window than on the earlier watches.  This style then carried over to the Hong Kong cased watches but without the Suwa symbol and with the alternate wording at the bottom of the dial.  I don’t know exactly when this change occurred but I guess we might consider the watches produced in 1981 as transitional in some sense.  You should be able to see the difference between the dial on this 1981 watch


and the more pronounced bevel on an earlier example


I thought I’d conclude this entry with a comparison of an authentic early 6309 dial fitted to an old watch of mine, now long gone with another fitted with a distinctly humdrum but typical aftermarket dial:

6309 authentic vs aftermarket dial

The obvious, glaring differences between the two are the generally poor quality of print on the aftermarket dial and the complete lack of a bevel on the day/date window.  You may also notice that the original watch on the left is fitted with very ordinary quality aftermarket hands and the watch on the right with the same flat style aftermarket hands illustrated earlier in the hands sub-post post above (set 3).  It is amazing how easy it is to spot the differences when viewing the two side by side but in isolation, the aftermarket dial does a sufficiently decent job to pass superficial scrutiny.  Buyer beware!

11th December

Movement:  Let’s take a look at the movement. We’ll start with the top first, viewed with everything still in place but with the movement removed from the case:

6309 movement topside

As usual at this point in proceedings, you can’t really judge the state of the movement with the autowinder in position but it does show some tarnishing which suggest a fair while since its one and only previous service. Removing the automatic winder framework and taking a look at its reverse shows the first indications that the service interval on this one has been too long:

6309 autowinder

It looks tidy enough but a closer look at the pawl lever pivot jewel shows dried, dirty lubricant

6309 autowinder closeup

most of which I think has migrated from a dried out fourth wheel hole at the centre of the barrel and train wheel bridge

6309 bridge grot

The state of this bridge makes me wonder at the condition of the fourth wheel arbor itself. Here’s a comparison of the current state of the fourth wheel

6309 worn fourth wheel

which may well clean up if the deposit on the end is just dirt, with a spare harvested from another movement

6309 fourth wheel

We’ll see how the original wheel looks post clean, but I am inclined at the moment to use the spare. If the fourth wheel has suffered from the lack of lubricant, I worry slightly too at the state of the hole in the train wheel bridge. Having recently acquired a 6319 for essentially nothing at all, I am thinking a spot of hot-rodding might be in order, four additional jewels in the 6319 train wheel bridge lifting the total jewel count to 21. Here’s the 6309 bridge (left) compared to the potential substitute:

barrel bridges

You can see here the pivot jewel now servicing the fourth wheel and a pair of diafix settings servicing the escape and third wheels. Further evidence of the how dry the movement is can be seen at the barrel arbor hole in the main plate

6309 mainplate barrel hole

and the barrel arbor itself

6309 barrel

The wear to the barrel hole in the main plate looks to have left a rather ragged finish which might need smoothing off before the movement comes back together if the barrel is to turn free from impediments.

Flipping the movement over, we can now check out the calendar side, day and date wheels in excellent, unmarked condition

6309 calendar side

The dismantling on this side starts with the removal of the brass circlip at the centre which secures the day wheel, followed by the removal of the day wheel itself:

6309 calendar

The two plates seated within the date wheel are the date wheel guard (top) and day jumper (bottom), the head on the thin arm directed to 4 o’clock slipping between the teeth on the wheel fitted to the reverse of the day wheel as it conducts its journey and serving to properly align the day wheel with the aperture in the dial.  With these two removed (below), we see a rather complicated-looking assortment of cogs sitting on the setting wheel lever and minute wheel bridge which sits between the setting lever and the hour wheel at the centre of the movement.

6309 setting lever

The minute wheel bridge actually has nothing much to do with the minute wheel other than to prevent it from becoming unseated from its post.  The dual purpose of the bridge lies in the intermediate wheel for day correction at its end which meshes with the star to the rear of the day wheel during the quickset process.  You should be able to see more clearly how this works from the following short video clip of the calendar mechanism in a partly dissembled spare movement:

You can see in the video the degree to which the setting wheel lever with its two wheels

6309 setting lever closeup

plays such a multitude of roles: at the first click on the crown, the corrector wheel (larger, bottom) meshes alternatively with the intermediate wheel for day correction on the minute wheel bridge to quickset the day wheel from one day to the next and in the other direction, swings over to quickset the date wheel.  In the time setting position, the intermediate setting wheel (smaller wheel, top) transfers rotation of the crown via the clutch wheel to the minute wheel which rotates both the cannon pinion on which the minute hand sits and the hour wheel on which the hour hand sits.

So that’s about it for part 1.  In part two (here) we’ll rebuild the movement, clean the case and put it all back together with fresh gaskets as required.