Seiko is well known for getting their 6139 chronograph to market in February 1969, the first automatic chronograph available to the public at that time. The story goes they wanted to release the twin register 6138 first, but because of the extra layer of components for the hour recording wheel it’s a more complicated watch than the single register 6139 and it wasn’t moving forward as fast as they’d like. Consequently they focused their energy on getting the 6139 to market to try and beat the two other contenders who were also developing automatic chronographs, namely Zenith-Movado group and a joint effort from Breitling, Hamilton/Bren, Heuer/Leonidas and Dubois-Dpraz. The arguments are still being done to death as to who actually was the first to market but my take is Seiko takes that accolade, your views may differ! This 6138-3002 came in for a full movement service as it wasn’t running correctly and a new crystal.

As can be seen from the caseback it has a production date of May 1977.

Once inside everything looks to be present, even the casing spring which is good.

With the movement uncased the dial and hands look to be in great shape now we can see them clearly.

Behind the dial you can see the smaller day indicator ring used in these models, that’s because the sub register pinions exit between the date and day rings.

With the rings removed you can see the extra layer which contains the drive and reset levers and hammer for the hour register.

This layer adds to the height of the movement.

With the top plate removed you can see the hour register wheel and heart along with the associated levers. The register is driven directly from the mainspring barrel arbor.

A view with all the components stripped.

The motion work side with the autowind bridge and rotor removed, you can see the column wheel at the top of the movement. As the start button is pressed this component rotes one click and denies the reset lever from being operated whilst the chrono is running. When the stop button is pressed it rotates one more click and a gap in the wall now allows the reset to be fully depressed.

With the bridge removed you can see the reset hammer and start/stop levers more clearly.

The movement was fully stripped ready for cleaning and inspection.

Once everything had  been through the vintage Vari-Matic the components were inspected, as suspected the running issues were down to a completely shot centre chrono wheel. I’ve talked about these before but the upshot is the clutch section should remain tightly shut when the levers aren’t operating on it, this disconnects the drive from the pinion. As can be seen from the original wheel on the right the clutch plates aren’t even touching each other rendering the component useless.

The rebuild commenced with the new centre wheel.

And continued until she was ticking away merrily.

The date rings were added….

….and the dial and handset were refitted. One complication with changing the centre wheel and keeping the original hand is that the pinion that the pipe of the hand fits onto isn’t round it’s actually a “D” shape. When the hand is pressed on, the pipe takes the shape of the pinion and this prevents any slippage occurring. Unfortunately when a new wheel is fitted the pinions are very rarely in the same position at rest as the one it’s replacing, so the hand has to be forced on in a different position which can mean splitting the pipe if you’re unlucky. Fortunately this one went back on relatively smoothly.

The crystal was the next issue. Original crystals for these come as a unit with the chrome surround because they are bonded to it, unfortunately NOS crystals are very hard to source these days. The only solution is to force the crystal out of its surround and clean the old adhesive off.

Once this is done you can buy a correctly sized crystal and bond it back in. The profile is slightly different as the crystal is slightly thinner but it’s the only choice unless an original can be found.

The new glass was glued and cured…

….then fitted in place and she was finished. Another iconic chronograph back in the land of the living!