Thursday, September 27, 2012

A short ramble on the caseback transformation of a 1964 Grand Seiko Chronometer

A short ramble on the caseback transformation of a 1964 Grand Seiko Chronometer


The 1964 Grand Seiko Chronometer (caliber 430 / 43999) is a landmark timepiece, introduced by Seiko during the year of the 18th Olympiad in Tokyo. Seiko timed the games flawlessly, and their success at the 1964 Olympic Games gave Seiko international respect and credibility. 

In 1964 Seiko entered the Astronomical Observatory Chronometer Concourse in Neuchatel, Switzerland for the first time and secured a 144th and 153rd place amongst the worlds finest chronometers. In 1967, SEIKO secured 4th, 5th, 7th, 8th and 12th place in the Chronometer Concours, winning 2nd and 3rd place in 1968. In 1969, with the advent of quartz movements, the Observatory contests of Neuchatel ended. During the early 1960s Seiko displayed the 'Chronometer' name on selected, precision watches which had passed the in-house Seiko chronometer standard testing, the equivalent of the BO (Basel Observatory) Chronometer standard, but stopped displaying the ‘Chronometer’ designation in 1966 due to the lack of independent CICC Certification facilities in Japan. Today, precision Seiko watches displaying the simple ‘Chronometer’ designation are a rarity sought after by collectors, and perfectly reflect Seiko’s “finest decade”.

Caliber 430 (43999) Chronometer movement

Concealed below the subdued, pearl silver sunburst dial with faceted, applied steel markers and the modest legend: "SEIKO Chronometer, Grand Seiko, Diashock 35 Jewels" beats a chronometer-grade movement defined by hand-selected and impeccably finished components, fine regulator, self-compensating hairspring, generous jeweling and large balance.

A movement of such significance deserves to be exhibited, and soon after acquiring this "second generation" Grand Seiko Chronometer, I began to examine the possibility of fitting it with an exhibition case back.

The exhibition case back quest begins

First attempts at fitting readily-available exhibition case backs for current Seiko models revealed that the thread diameter of the Grand Seiko was considerably larger than its contemporary counterparts. Searching for other commercially available exhibition backs - such as Invicta and Omega - proved fruitless. 

A custom-made exhibition back for the second generation Grand Seiko appears from time to time on Yahoo Japan, but is prohibitively expensive. For a year the project languished on hold while I pondered the situation. In the interim, a wallpaper of the movement on my iPhone kept the worst withdrawal symptoms at bay...

Finally I turned my attention to the existing case back. The Chronometer movement is cased in a heavily-lugged stainless steel case with threaded caseback.

The case-back shows the original 18k Gold Lion medallion used to denote “chronometer-grade” pieces.  The case back on my example was heavily worn, and I began to consider the possibility of converting it to an exhibition back by machining it to remove the medallion, similar to the 4520-8000 case back that had it's medallion cut out of the original back to convert to a display back: 

With this in mind, I posted a request on SCWF in an attempt to find someone willing and able to perform the conversion.

Months passed, and apart from some PM's offering some suggestions, my search remained fruitless. Until two months ago, when I was contacted by a forum member (who wishes to remain anonymous) who offered his help on the condition that the original case back remain unmolested, in order to maintain the historic integrity of the Grand Seiko. The correct way to obtain an exhibition back, he admonished, would be to source a more common case back with the same dimensions as the original, as a base for the conversion.

The breakthrough

As I had earlier explored the possibility of a donor case back, it had become apparent that the dimensions of the GS case back where not standard, as least not as far as commonly available case backs where concerned. Now encouraged, I borrowed a digital micrometer and was able to measure the following dimensions:

I then googled "seiko case back 31mm" and found a reference to a 7T32 (Quartz) case back. Grubbing through my parts box I found a 7T92 and lo and behold the caseback fitted:

However, due to the thinness of the quartz movement, the case back is a lot shallower than the original, so snugging it down stopped the movement (oops!) while backing off just slightly freed up the movement again. Clearly, not the solution to our problem!

Our next tactic was to consider the case number itself, in order to determine if we could glean some useable information there. Although no case number was apparent, the GS 43999 is identical to the GS 5722-9990/9991, so I assumed the case number is 9990/9991 (and possibly the same case as the King Seiko 44-9990 and 4420-9990 chronometers, although this remains to be confirmed). However, I also found the 9990 case number used on early 60s 6xxx caliber dresswatches, but this is a completely different case. Pretty much a dead end.

What we did have to go on, however, was a small sliver of information: the case back gasket number for the 7T calibers is FH3080B0A, so any non-quartz case back using a XX308XXXX gasket might be a matching fit. On we could see that the Seiko 7009 (5110,5140,5150,5160,5180,5200,511A,520A) also uses a FH3080B0A caseback gasket, and I considered picking up a parts donor on eBay to confirm fit and clearance - the depth of the case back to accommodate the rotor should give plenty of clearance to the hand wind 43999 movement. I was, however, warned that the 700x cases have a different design with respect to gasket fitting, and was linked to Jules Borel instead, who listed the FH3080B0A gasket as being compatible with a number of 6309 caliber dress watches. Reference to a casing guide revealed that the 5722's case gasket number was, in fact, 0C3160B (circular cross-section).  

However, the 7T32 case back had actually fit, although it was too shallow, so I figured the dress 6309s might be worth a shot - maybe I should get a parts donor of one of these? And then... I remembered the 6309 sports watch donor which I used some years ago to replace the balance on a 6309-7040 diver (described here:

The 6309 case back actually fit perfectly, the flange of the GS caseback has the same dimensions ie: 31mm thread, 33mm total diameter.

The caseback screwed on smoothly and snugged down, indicating the threads where matched, and the 6309 case back  was 0.5mm thicker than the GS caseback (3.0 mm vs 2.5mm). 

The transformation begins

We decided to go ahead with a cut-and-hope tactic, as the case back from the 6309 sports watch was expendable and thus an excellent candidate. The next decision to make was whether to cut the aperture into the flat surface (22mm) or onto the slated surface (permitting a 25-27mm aperture). At this stage we where still faced with a number of unknowns, including the feasibility of cutting a crystal seat on the slanted surface of the case back, and the possibility of deformation when machining a larger aperture.

A mock-up started with an approx 22mm cut-out- followed by an approximately 24 and 27mm cut-out. At 24mm there was certainly more shown of the movement, with less of a port-hole effect, and less shadows around the edges. 27mm was considered too large, as this might compromise the rigidity of the caseback. A 0.8mm thin, 25.4mm diameter sapphire crystal was duly sourced, and the 6309 case back was slipped in the post.

The donor case back had previously been gouged, so the decision was made to attempt to machine the gouges out, leaving the surface unpolished in order to highlight the polished surfaces of the chronometer movement which where to be showcased.

Finally, the machining of the aperture took place, and the crystal was fitted with an adhesive that is cured with both heat and UV light - slightly flexible once cured, and not given to discoloration over time. 

The end result, I think, speaks for itself...

The first time I saw that movement with the fantastic apellation "Chronometer" etched in gold, I knew I had to have it displayed. Friends and colleagues (many of them WIS themselves) shake their heads at my passion for this specific GS, but the 43999 movement is so breathtakingly beautiful that giving it the chance to speak for itself, the balance wheel pulsing under sapphire, will certainly open a few eyes. But most importantly, I will have the thrill of enjoying the movement on a daily basis, exponentially increasing my appreciation of this - for me - most significant of watches!

This post closes with my heartfelt thanks to the SCWF forum member who made this possible. In spite of a busy schedule, he took the time to answer my questions patiently and in great detail. The quality of the work done, and the attention to detail are truly outstanding. My appreciation of his extensive help and encouragement are unbounded, and I have got a lot of karma to pass on. This is truly the essence of a great forum… at the end of the day, nothing can ever match the forum members themselves and their fundamental helpfulness and willingness to contribute their - often hard earned - knowledge and experience!


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