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In spite of the numerous potential pitfalls involved in buying a classic Seiko automatic chronograph, I found myself bidding on another eBay auction, this time a black dialed 6139-6012 and winning it. The dial and handset looked mint, the case a little tatty with plenty of grime in evidence, but more problematically (and perhaps predictably), the movement was running very slow, and the chrono function was, more worryingly, out of synch with the rest of the watch. This latter problem is a sign of the common symptom in these watches of a slipping chronograph clutch with the result that the forward momentum of the second hand at each tick, causes the clutch to slip, impelling the hand forward more than it should, with the chrono then appearing to run faster than the watch. I had this same problem on the blue 6139-6005 described in an earlier post, and the watchmaker who serviced it for me (Richard Askham) solved the problem by replacing the chronograph centre wheel. You can see the clutch ring on this cross-section drawing taken from the service document for the 6139A:

With Richard no longer working on these movements (due to the shortage of parts), it looked like I had a paperweight on my hands. I did make enquiries with another recommended watchmaker in Bristol, but their estimate was well into three figures, and so that appeared to be that and at this point I shelved the project.

And then, a month later (July 2010) I spotted another 6012, this time a gold faced dial.  I figured it might be worth a shot to see if the movement could be transplanted into the black dialed watch and so I bid, and won this one too, again for peanuts, and in due course it arrived.  But luck was not on my side and the movement in this second watch was barely running at all. So, I now had two paperweights. Here they are:

At this point, the two watches assumed a rather forlorn position in my parts drawer, where I would encounter them from time to time over the following few months as I foraged for other parts.  But slowly my courage gathered itself up and, with nothing whatsoever to lose, and everything to gain, I started to wonder how much more difficult could a 6139 be to service than a 6309, 6119 or 6106, all of which I had stripped and rebuilt on numerous occasions.  The base calibre of the 6139 is, after all, a 6106. I decided to attempt a service of the movement fitted to the golden dialed watch because there was the possibility that the chrono centre wheel on this one was ok. I would then fit the black dial and handset assuming all went well. Cosmetically it also looked the cleaner of the two.

I started the process expecting it to be no more than a learning exercise, and to have a movement at the end that might run, assuming I could reassemble it, but not realistically expecting the chronograph to function correctly. So, we start, having removed the hands, with the top of the movement, auto-winder removed, revealing the pawl lever seat, the pawl lever and the transmission wheel, all part of the automatic winding mechanism:

With these parts removed we get a better view of the chronograph bridge which supports the hammer click (the mechanism that provides the resistance you experience in pressing the reset button) and which I’ve unhooked from the nipple on the hammer, and the minute recording jumper:

Next, we remove the chronograph bridge and get a good view of the minute recording wheel (the cog on the left), the intermediate minute recording wheel (next to it on the right) and the centre chronograph wheel (north north east from the intermediate wheel. To the left of that you can see the reset hammer that snaps the second hand and minute recording hand back to their zeroed positions when you push the reset button:

With the coupling lever spring (top above) and hammer spring (left above) and hammer all removed we see the two coupling levers whose job it is to lift the clutch ring off the fourth wheel when the chronograph is stopped (see diagram above). When it restarts (by pressing the upper chrono button) the clutch ring is released and is pushed down onto the fourth wheel by the clutch spring. The slippage I was experiencing with the black dialed watch may have been due either to a weak spring, or perhaps to clutch slippage due to muckyneddy on the clutch surfaces and/or fourth wheel.

Now, with the minute recording and intermediate wheels, plus the levers removed, we have a better view of the chronograph wheel. You can see here the chronograph finger curving round at the bottom of the wheel whose job it is to transmit the instruction to the minute wheel to turn one click, once per revolution of the chronograph centre wheel. For this to work properly the chronograph finger has to be properly aligned with the teeth on the intermediate minute wheel.

Here’s the chrono wheel out of the watch:

With the barrel, chrono wheel, balance and centre wheel bridge removed we have just the pallet cock, fork and staff and escape wheel to go

Here are all the bits and pieces

ready for this:

which contains ammoniated watchmaker’s cleaning solution.  While that’s doing its thing, we can turn our attention to the case

which needs a jolly good clean, as you can see here:

After the toothbrush, toothpaste and if memory recalls a go in the ultrasonic bath it is looking a bit better

With internal bezel, bezel ring, crystal gasket back in place

the case is ready to receive its lovely new crystal, courtesy of Sternkreuz via Cousins

A nice view of the internal dome here:

Onto the case, looking good

on with the external bezel

and we hit a snag. I cannot get the bezel to seat properly, no matter how much force I exert with the crystal press. In the end I realise the problem lies with the crystal. It is too deep and the bevel is fouling on the inner diameter of the bezel. I fitted one of these to the 6005 discussed earlier without any such problems but had heard from others that sometimes they don’t fit. The solution required simply sanding down the bottom edge of the crystal until it fouled no more.

With the movement bits clean and shiny, the movement reassembly and oiling proved reasonably straightforward, with the exception of one issue that I’ll get to in a moment.

With the hands test fitted, the problem that revealed itself was that neither second nor minute register hands were resetting properly.  Perusal of the service sheet for the 6139A does not offer much comfort to an amateur such as myself, suggesting polishing the setting surfaces of the hammer to get it to contact properly with the minute and second hearts, located respectively on the minute register wheel and chronograph centre wheel. However, this is not a 6139A but a 6139B, and those clever chaps at Seiko had installed an eccentric screw to allow you to change the balance between the two registers. You can see it in the photo above just below the pillar wheel. I suspect that at some point in the disassembly process, I had tampered with said screw upsetting the balance between the two registers. A 180 degree turn was all that was required to effect a cure. You will note also in this photo that the minute register wheel has changed colour as has the hammer. This is because in attempting to find a diagnosis for the problem I substituted these two components from the other watch.

In this shot, I am depressing the reset button which impels the hammer to impact upon the two hearts, resetting the two registers.

A close-up of the chronograph bridge shows the chrono finger and minute recording jumper correctly seated in relation to the teeth on the intermediate wheel and minute wheel respectively.

You can get an idea of what is involved in setting this up properly from the following

I hasten to add that it all simply worked when I reassembled the movement – no adjustment required on my part, which is just as well.

At this point, we are ready to pop the hands back on, having swapped the dials between the two movements. First, on with the hour hand, the movement temporarily housed in the other (uncleaned) case:

then the minute hand

and then the minute register hand

At this point another hurdle. The red second hand originally fitted to the black dialed watch is effectively dedicated to the chronograph wheel fitted to that movement, but we have swapped movements. Fitting the hand to the replacement movement resulted in it being misaligned when zeroed. This happens because the shaft on which the hand is seated on the chrono wheel, is profiled thus

to prevent slippage when zeroing. And there is no guarantee that the shaft will be oriented in the same way on every movement. So a new chrono wheel requires either a new hand or for the old impression to be filed out from the inside of the tube with a cutting broach – something which can often still leave the hand insufficiently well secured. Unable to source a replacement hand of the correct colour, I resolved to paint the yellow hand originally fitted to the gold faced watch

As it had originally been mated with the chrono wheel now fitted to the black faced watch, it should align correctly when zeroed. After much experimentation, the correct colour and consistency of paint was obtained by mixing some red railway modellers emulsion,

with some GlasArt blue transparent paint, to get the correct brownish tinge to the red colour, all thinned out using lighter fluid. The resulting finish is excellent and the colour match almost spot on. The hand re-seated without further trouble (remembering to depress the reset button when fitting). Next up, remove the gaskets from the crown and pushers

fit new, greased gaskets (fiddly as hell)

and we are on the home straight.

and a wrist shot

Those of you fed up with every watch ending up on the ubiquitous NATO strap might hanker after a bit of steel.  These watches would originally have been fitted with a bracelet such as these:

Mine came with one, in slightly tired condition, but a bit of elbow grease soon had it looking decent once more:

In spite of its ordeal, in the week following its reconstruction, it gained a total of 12 seconds.  Not bad I reckon.

Post script:  For more on this 6139 see here.