Bell-Matic: The Seiko 4006-7021

Tags

4006, Bell-matic, Seiko, Vintage

In the world of the watch cognescenti, Seiko are routinely not assigned quite the credit that they deserve.  On watch forums heated arguments flare out of nothing at the suggestion, for example, that a higher-end Seiko model might somehow be spoken about in the same breath as watches emerging from the giddy heights of the Swiss Jura. Horological innovation though does not emerge necessarily just from the top of the market:  the position occupied in the public consciousness by Rolex has its roots in Rolex’s record of making no-nonsense, superbly engineered, yet elegant divers and sports watches in the 50’s and 60’s, many of which were widely used as tool watches, instruments designed to serve some sort of purpose other than simply as a status symbol. Firsts widely credited to Rolex include the first waterproof watch, the first self-winding movement and the first watch to display the date.  Equally, brands such as Seiko whose centre-of-mass occupies a market position somewhat south of that of Rolex, are responsible too for their fair share of landmarks, often deriving from innovations made in mass-market watches designed for the every-man and woman. 

The 1960’s were a fruitful decade for Seiko: I’ve documented some of the truly iconic divers watches made by them through the 60’s and 70’s as well as the automatic 6139 and 6138 chronographs, both of which represent significant landmarks in the development of the wristwatch.   In addition then to these more high profile contributions, the Bell-matic slips rather under the radar although to those in the know, they are beautiful, dignified and fantastically engineered watches.

The first Bell-matic, the 4006-7000, was introduced to the Japanese domestic market in mid 1966, fitted with a 27 jewel version of the 4006A automatic movement, the first automatic alarm movement fitted with a centrally pivoted full rotor.  The alarm complication at that time was hardly a novelty though, having been first introduced in a wristwatch in the early 1900’s by Eterna.

That watch though was essentially an adapted pocket watch and the first ‘genuinely operational alarm wristwatch’ was the celebrated Vulcain Cricket of the late 1940’s whose alarm was notable in serving its intended purpose of being capable of waking its wearer from their slumber.  The first automatic alarm wristwatch was the Memovox produced from the early 1950’s by Jaeger-Lecoutre which used a bumper rotor to wind the movement. In its modern incarnation, the Memovox has been hugely refined and features a full rotor, a feature Seiko introduced with the 4006-7000 in 1966.

These days, of course, an alarm complication on a mechanical watch seems a bit prosaic, but one should not underestimate the power to delight of a chime or tring produced from the movement of a hammer on a resonator rather than as the result of an .mp3 file being played through the speaker of a smart phone.  As I have mentioned elsewhere here, my own fascination with the Bell-matic derives from the fact that my father wore one for 20 years or more from the late 1960’s, and it assumed a position in defining who he was at that time as much as the endless chain of odiferous Cuban cigars!

So let’s get to the point of this particular entry.  Over the past couple of years, I’ve accumulated five or six Bell-matics, four of which have been sitting patiently in the ‘to do’ pile.  Having recently tied up a few loose ends needing my attention, I turned to my youngest son for assistance in selecting the next project and he immediately picked out the watch you see below, a 4006-7021 from December 1969. 

This particular watch features a 17 jewel version of the 4006A, a reduction in jewel count over that of the earlier watches made out of necessity, apparently because high jewel count watches attracted a premium import tariff in the US market in the 1960’s making the 27 jewel variant too expensive to sell there.  The 27 jewels were consequently reduced initially to 21 in a couple of models sold into the US market, but by mid-1969, all Bell-matics used the 17 jewel version of the movement.*

This particular example makes a decent first impression:  the crystal is on the tatty side, the case sports a few dings, the bezel in particular a little ragged.  The dial and surrounding alarm ring though both look in excellent condition and so on the whole there is plenty of incentive to make a go of this one.  Closer inspection of the case suggests that a long time has passed since anyone ventured into the interior.  The case back is in super condition, but the backs of the lugs are filthy:

Removing the case back reveals a mid-case bulging at the seams with the 4006A movement.

The movement looks plenty dirty and with what appear to be a few short bristles or hairs distributed fairly liberally about the place.  To remove the movement, we need to release not only the winding crown and stem but also the alarm button.  The former is released in the usual way by depressing the setting lever axle whilst the alarm button requires the push bar to be depressed:

With these two out, we are greeted by the full horror of what lurks in the vacated hollows:

Probably best not to linger here too long so instead, let’s take a closer look at the movement, with rotor removed:

Apart from the grime, it all looks exceptionally nice under the hood and as you can see, with barely any power in the mainspring, it can’t help but lazily swing into action.  Two key features worth pointing out at this point are the alarm hammer and sounding spring, the operation of which we shall investigate in due course.

With the movement out, the first task is to remove the dial, hands and alarm setting wheel.  This unrestricted view of the dial confirms the excellent first impressions – it really is in near mint condition, although the hands slightly less so:

The alarm setting wheel which surrounds the dial is removed by unscrewing the two securing tabs at each side and lifting it off:

With the alarm setting wheel removed, we can gain access to the dial feet screws, remove the dial and hands and take a look at the calendar wheels:

Again, everything here looks in tip top shape.  Removing the day and date wheels reveals the unlocking wheel which plays a key role in the operation of the alarm.

The unlocking wheel sits on top of the hour wheel and in the comparison below you can see that the three protrusions on the hour wheel will align at the appropriate point in its journey with the three holes in the unlocking wheel.  When that happens, the hour wheel lifts, and that action raises the disconnecting lever beneath, which in turn releases the alarm hammer to perform its task.

You can see how this works in the figure below taken from the 4006A technical document:

The calendar plate comes off next, exposing the somewhat intimidating complexity of the alarm and setting components but providing a clear view of the relationship between the disconnecting lever and the alarm hammer and alarm wheel.

The calendar plate on this watch was swimming in congealed oil but you can still appreciate what a nicely finished component it is, the decoration being entirely hidden from view when fitted:

The disassembly of the calendar side requires a measured, methodical approach, with plenty of opportunity to lose key components or forget the significance of triple-slotted screw heads.   Here’s a shot with pretty much everything removed barring the setting components

Over to the top of the movement next, and we can get an idea of how the power is wound into the alarm mainspring and then subsequently transferred to the hammer.  In the photo below we see how winding the crown transfers torque via the crown wheel to the intermediate winding wheel and on to the alarm ratchet wheel, thereby winding power into the alarm mainspring.  When the disconnecting lever lifts, the alarm mainspring power is released via the alarm intermediate wheel to the alarm wheel beneath whose rotation causes the hammer to vibrate back and forth against the sounding spring.

With the mainplate stripped of most of the remaining components, we see how the alarm mainspring sits openly within the mainplate.  We leave it in position for the cleaning step together with the balance cock and balance, minus its diashock setting.

Cleaning, lubrication and reassembly proceeded pretty much without incident, with no parts requiring replacement, nothing getting lost and generally no significant hiccups.

Diashock oiling and fitting to the balance, taking care not to mix it up with the mainplate Diashock setting which has a lower profile

and as you can see from the fourth shot above, she runs!  I am inclined to skip through the remainder of the reassembly process as there is a danger of information overload with as complex a movement as this one, so lets pause only to look at both sides, almost complete; first the top side:

and the calendar side, minus the day wheel

On with the day wheel and film washer

the dial

followed by the alarm setting wheel and hands

The alignment of the alarm ring requires you to wind power into the alarm mainspring, pull the crown out to the first click and rotate anticlockwise until the alarm sounds with the hands set to 12 sharp.  Check the clearance of the hour/minute hands (remembering that the hour wheel lifts when the alarm sounds) and then refit the alarm ring with the pointer aligned with the hour hand.  Fix and check again.  The tolerance is supposed to be plus/minus 5 minutes but I managed to get mine more or less spot on.

With the case cleaned and a fresh crystal fitted, we appear to be heading down the finishing straight

The movement requires a bit of jiggling to seat happily in the case

and with the automatic winding mechanism and rotor fitted, we can run it through its paces.

The only fly in the ointment at this point was a sticky alarm setting wheel.  Out of the case, it rotated with no problems but in the case, it was sticking, eventually refusing to budge.  The culprit turned out to be the crystal, a facsimile made by Sternkreuz but whose inner profile and/or steel tension ring was causing the alarm ring to foul.  A temporary fix for the moment has been to remove the tension ring

while I wait for a couple of original Seiko 325T02ANS crystals to make their way to me from the USA.  I am also waiting for a button gasket to arrive, also from the US but making do for the moment with a generic gasket from Cousins.

As usual then, let’s finish with a few shots of the completed watch:

and three more fitted to a Hirsch Duke

* As I have a 27 jewel 4006-7010 from 1970, I suspect this piece of intelligence may either refer to US market watches or simply to new models introduced from about 1969.