Seiko 6159-7010 ‘Tuna can’

Seikos professional range of dive watches started in 1968 with the introduction of the 6159-7001, this was a traditional type of divers watch albeit with a monocoque case and was water resistant to 300m. Now the Japanese at this point were excellent at taking design cues from other manufacturers and incorporating them in their own watches, but in 1975 they released the 6159-7010 which was a truly unique and original design of their own. It included several industry firsts, the first titanium case, the L-shaped single crystal gasket and of course the ceramic-coated titanium shroud. With a 600m depth rating, the 6159 dispenses with a helium release valve in part due to very consistent and tight manufacturing tolerances, but also due to the one piece case and screw down crystal retaining system. This means that the crystal cant blow out as atmospheric pressure drops in a decompression chamber as it’s physically restrained by a locking ring. It’s not hard to see how this watch earned the nickname ‘Tuna can’! The watch featured came in for a movement service.

Seiko 6159-7010 tuna

As can be seen from the back it has a production date of April 1976.

Seiko 6159-7010 tuna

The first job is to actually get the movement out of the case, for this to happen I have to remove the titanium shroud….

Seiko 6159-7010 tuna

….then the rotating bezel. This leaves the locking ring accessible….

Seiko 6159-7010 tuna

…which is undone in my 5700 opener. It’s important to use a decent tool to undo these as once the edges of the notches are worn they can be almost impossible to remove!

Seiko 6159-7010 tuna

Here’s a shot of the different components from the chapter ring upwards.

Seiko 6159-7010 tuna

I still can’t remove the movement yet as there’s a seal that cushions the movement against the case, this needs to be removed….

Seiko 6159-7010 tuna

….to give access to the stem release button.

Seiko 6159-7010 tuna

The movement is now released so the dial and handset can be removed.

Seiko 6159-7010 tuna

With these out of the way the date disk can be seen, it also allows me to flip the movement over….

Seiko 6159-7010 tuna

….into a Seiko 45.61.70.09 movement holder so I can remove the oscillating weight!

Seiko 6159-7010 tuna

Once this is off it tells a story, the weight has obviously been contacting the movement as can be seen by the wear marks on the plate. This will have to be addressed later on but I will say it holds the honour of having the most worn rotor bearing I’ve ever seen that’s still in one piece!

Seiko 6159-7010 tuna

With the autowind bridge removed I saw that the plate was soaked in oil, it had probably been applied to the rotor bearing at some point and too much had been used. This movement is a calibre 6159b as opposed to the earlier 6159a. Crucial differences are the rotor bearing is pegged and screwed on the earlier model and is held by a slot and a single screw on the ‘b’. The balance also received a bit of work, they both have micro adjustment but the ‘b’ has the addition of adjustable curb pins which can be seen added to the regulation arm on the balance. Both ‘a’ and ‘b’ are 36,000bph, 25 jewel automatics, both with hand winding and hacking.

Seiko 6159-7010 tuna

The balance is removed in this shot revealing the pallet fork and rhodium plated bridge.

Seiko 6159-7010 tuna

With the balance off I turned the movement over to start on the calendar side.

Seiko 6159-7010 tuna

The keyless work has seen some corrosion at some point, particularly the lever with the wig-wag on the end of it, but it seemed to have been stabilised at some point in the past. Everything worked as it should do which was great.

Seiko 6159-7010 tuna

This side was soon stripped ready for me to continue on the motion work side.

Seiko 6159-7010 tuna

The power was taken off and the ratchet wheel removed, then the pallets could also be taken out.

Seiko 6159-7010 tuna

With the bridge removed the train is now visible, there’s lots of teeth on that 36,000bph escape wheel!

Seiko 6159-7010 tuna

The rest of the components were removed and the observant amongst you will have noticed the legend ‘Do Not Open’ printed on the barrel cover. This should read ‘Cannot open’ as the barrel wall is flanged over the cover to prevent it being taken apart.

Seiko 6159-7010 tuna

I’ve been practicing a method of getting these open on a barrel kindly donated by a collector from Thailand, and more importantly getting them closed successfully after cleaning! Having do not open on the barrel is fine when replacement barrels were still being manufactured and you could just drop a new on in, however these haven’t been produced for at least 25 years now and I’ve only ever seen pictures of NOS ones! One of the most important jobs when servicing a watch is cleaning the barrel and mainspring so I can now say I’m able to do so on the 6159!

Seiko 6159-7010 tuna

And if there were any doubt as to why you shouldn’t ignore a mainspring here’s what 39 years of muck looks like.

Seiko 6159-7010 tuna

Seiko 6159-7010 tuna

This is my essence jar, it’s so called because it’s used to keep essence of renata in which is a horological degreaser. I clean off very dirty components in the jar before they get put through the cleaning machine, this way the cleaning fluids in the machine last a lot longer. This jar of eor was fresh before I put the barrel and spring through it!

Seiko 6159-7010 tuna

With that the watch was fully dismantled and ready for it’s trip through the Vari-Matic.

Seiko 6159-7010 tuna

Seiko 6159-7010 tuna

Whilst the components were being cleaned I turned my attention to the case, I refitted the crown and crystal and gave it a 6bar leak test.

Seiko 6159-7010 tuna

Seiko 6159-7010 tuna

Seiko 6159-7010 tuna

Not that this vintage piece is going to be going to 300m anytime soon but it’s nice to know it’s safe to swim with. Once the parts were cleaned the re-assembly began starting with the mainspring.

Seiko 6159-7010 tuna

Using my patent method the cover was successfully re-fitted!

Seiko 6159-7010 tuna

The train and bridge were fitted….

Seiko 6159-7010 tuna

….then the ratchet and balance. The power was wound on and the timing could be roughly set.

Seiko 6159-7010 tuna

The calendar side was fairly straightforward….

Seiko 6159-7010 tuna

Seiko 6159-7010 tuna

Seiko 6159-7010 tuna

….which meant I could then concentrate on that worn rotor bearing. The actuall bearing is the same dimension as those used in any 61xx calibre so I found a good one from a 6139 and decided to try and transplant it into the 6159 framework. This is taking a risk as once the old bearing is punched out inevitably some of the tabs break off and compromise the strength of the framework. However as the bearing was absolutely shot I had little choice.

Seiko 6159-7010 tuna

The bearings were punched out using my ex Ministry of Defence staking set!

Seiko 6159-7010 tuna

The replacement bearing was staked back into the 6159’s framework and appeared to be holding firm. Good stuff!

Seiko 6159-7010 tuna

The rotor was refitted and it now turned smoothly with no catching anywhere….

Seiko 6159-7010 tuna

….this meant I could now refit the dial and hands and recase the movement.

Seiko 6159-7010 tuna

The crystal was refitted and the watch was put on the final test machine to check for problems. There’s no point putting the bezel and shroud back on if the regulation needs any further adjustment!

Seiko 6159-7010 tuna

When I came to check the watch 24 hrs later I could hear the rotor rubbing on the case and movement, unfortunately the framework couldn’t hold the bearing tightly enough and over the initial 24hr test period the rotation of the weight had loosened it enough to allow the rotor to start catching again. To my dismay this meant I needed to source a replacement 6159 auto framework which is no easy task, but to my astonishment I actually managed to track one down! However my excitement was short lived, when the NOS framework was delivered it was for a 6159a and if you remember one of the differences from the ‘b’ is the way the rotor attaches to the bearing.

Seiko 6159-7010 tuna

After discussion with the watches owner (who makes the most fantastic watch straps by the way!) it was decided that as a search for a replacement could take months, the pragmatic approach would be to fit the framework from a 6119 which is identical apart from the engraving. This would allow for the watch to be worn and used whilst the search continued.

Seiko 6159-7010 tuna

The transmission wheel, cover, pawl and screws were swapped over as these are slightly thinner on the 6159 – no, I didn’t know either until I tightened the bridge down and the movement stopped!

Seiko 6159-7010 tuna

The 6159’s rotor was also replaced as after closer inspection I noticed it had been ground down slightly, obviously to try and increase the clearance between it and the movement to compensate for the worn bearing. This ultimately affects the weight and the winding efficiency so a new rotor was fitted, apart from the 6159a these are thankfully identical across the 61xx calibre range so I had a few good ones in stock.

Seiko 6159-7010 tuna

The movement was recased and no further scraping noises were heard on test so the bezel and shroud were refitted and the job was done. A fantastic historic Seiko, in the condition I love (wearable!). I want it 🙂

Meanwhile if anyone has a 6159b auto framework with bearing in serviceable condition, contact me please!

Seiko 6159-7010 tuna

Seiko 6159-7010 tuna

Seiko 6159-7010 tuna

2 comments

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