Seiko 7A38 - by the numbers



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Forum Home > Bend it, Mend it - Mods & Wreckers > Those 'just-jobs'

Sir Alan
Posts: 458

With a choice between the Wimbledon mens final (Murray vs. Federer) and the British Grand Prix on tv, I thought I'd catch up on some of those little jobs I've been putting off while playing couch potato.

First up was the 7T27-7A20 I've just bought off ebay. Badly scratched glass, case in good condition but movement sold as not working. I replaced the glass (with an XMF320.927) and then took a look inside to see if I could coax it back into life. Unfortunately not - it was dead though there were no obvious sign as to the cause. :(

So, onto something I'd been considering for a week or so, when I saw this come up: 

A nice looking 7T27-7A10. I'd meant to bid on (and win this), but didn't - one of those in hindsight mistakes.

I already own one, really liking the dial (very colourful) but finding it just a bit too small to wear. So, time for a bit of mix-n-match.

The movement in the 7T27-7A20 was a 7T27B. It came out easily (I'm very familiar with the 7Txx movements) and then I had the prospect of removing the hands (easy), the dial (tricky, it was on tight) and then the date ring.

I'd not done one of these before, but figured as the movement was dead, I had nothing to lose. The date ring is held in place with a very thin plate, part of which is a finger spring (see below at the number 30 mark) - much like the assembly on the 7A38. Unlike the 7A38, this plate is held in place by two plastic 'screws', which are released by a quarter turn. Once the plate was free, the date ring (white on black) was free.

Now I had to dissassemble the good 7T27-7A10 (risky but I'd decided I was going for it). Inside I found a 7T27A movement. This is (I think) a first generation of the 7T27 movement - very very similar to the 7T27B, but with some differences (such as no PUSH hole for the crown release). I've seen very similar differences on the 7T32A/B and 7T34A/B movements.

All dimensions looked the same and the dial fixing holes were in the same place.

So, it was off with the date ring (black on white) and the swap. Then on with the grey spacer (between movement and dial) - this was smaller than the one from the 7T27-7A10, and on with the dial.

I put those little rubber finger tip protectors on for this, I needed to press the dial firmly onto the movement and didn't want to get oil/grease on the dial.

Finally, on with the hands.

I'd not fitted hands for a while but really took my time trying to line them up on the marks. I think I did a pretty good job. Then, it was in with the battery and back in with the crown and that moment of truth ................

Tick, tick, tick and all is good.

I just need to get it a nato strap and we're away.

Given this had gone so well, I decided to do another. Next up was my 7A38-701B 'vulcan'. The hands (and in particular the chrono second hand) weren't hitting their marks, but more importantly (and annoyingly) the chrono second hand was reluctant to start at times. The seller had pointed this out, so it wasn't a surprise but I couldn't keep it like this.

So, it was time for a donor movement, and out with the tools (again!!). The only tricky part here was the day and date ring swap (the donor movement was black on white) but I have to say it went perfectly. I've got the technique for doing this sorted, including moving the finger spring aside for the day ring. Then it was back on with the dial, the hands - paying special attention to the chrono hand and voila:

and, all the functions work as they should. 8)

(I also replaced the chrono second hand - the 'original' was slightly bent, and all the sub-dial hands)

Finally (I was on a roll), I decided on the job I've been putting off the longest.

One of my first 7A38's was a 7A38-7070, which came with the lume on the hour and minute hands quite badly degraded. This along with the polished edges made them quite hard to see which was a shame given how legible this dial is.

Paul very (very!!) kindly sent me some hands as a gift. Well, I wanted to do them justice - here they are:

a real improvement, and a very nice gesture. :D

That's it for today.

July 8, 2012 at 2:31 PM Flag Quote & Reply

Site Owner
Posts: 14381

Glad to see you finally put them to good use, Simon. ;)

As you know those hands came off a water-damaged 7A38-7070, sold to me by DaveS, back in August 2010, which I later re-built.

They're not mint, by a long way, and you can still see the tarnish on the polished edges of the minute hand in your first photo ....

But I think they work pretty well with the aged lume on your dial - and like you say, they're a real improvement on the previous set. :)

July 8, 2012 at 3:42 PM Flag Quote & Reply

Posts: 18

Hi Sir Alan! Quick question, I'm having a nightmare releasing the stem from my 7T27B movement. I'm starting to think I'm doing it wrong. Can you please confirm how you release it? I've been applying pressure to the hole which says "push", directly above the "Japan" graving, but there seems to be no give. Any advice/tips would be appreciated. Many thanks!

December 23, 2013 at 6:16 PM Flag Quote & Reply

Site Owner
Posts: 14381

Pull out the crown to the first click / setting position. A tiny release lever should magically appear in the hole. Press down on that. ;)

I'm pretty sure that 'rule' holds good for all Seiko 7Txx movements. (Crown stem release in a 7Axx movement it's the second click).

December 23, 2013 at 6:38 PM Flag Quote & Reply

Posts: 18

Ahh, that worked, with a bit of force. Many thanks, you're a beautiful man :)

I did initially try releasing it after the first click, but it didn't withdrawl effortlessly, and I didn't want to force it, just in case it wasn't the right method.

Regardless, my efforts were in vain, because the movement seems to be dead. I've been Googling around for a new 7T27 movement but to no avail. The only results I get when Googling that particular movement is the RAF Gen 2 watch. Was that the only Seiko watch that had that movement? I was trying to find a cheaper, less collected watch, and replace the movement with that.

Thanks again!!

December 24, 2013 at 6:26 AM Flag Quote & Reply

Site Owner
Posts: 14381

December 24, 2013 at 6:51 AM Flag Quote & Reply

Site Owner
Posts: 14381

To me, those 'just-jobs' often include those that I deliberately put off tackling - because of the potential for screwing up and actually making them worse. This is one such simple job I've been putting off since before Christmas - and quite frankly been dreading. 

If you've read the last few posts in the Racer J39 thread, you'll know that the tip of the sweep second hand in my recently acquired J39027-70 was slightly bent. It was already like that when I received the watch, but if you've taken one of these Orient / Racer J39's apart you'll know how easily it can be done. On most J39's, the Tachymeter spacer ring sits directly on top of the dial plates. It isn't sandwiched between the watch case and bezel as in most conventionial Seiko 7A38's. This means that as you remove the movement, it drops down. But in an Orient / Racer J39 it doesn't come all the way out, because it fouls on the ends of the pushers and the crown tube. To remove a plastic Tachymeter ring from one of these watches safely, without risking breaking it, you first need to remove the pushers. What this means, is that if you don't remove the pushers (which of course you can't do without first removing the movement) the Tachymeter ring often drops part way down into the watch case and hangs - stuck diagonally. So if you're not careful, it can very easily foul that vulnerable sweep hand. Here's how that sweep second hand looked when I first photographed the movement:

Because the distortion to the sweep hand was limited to just the very tip, I'd decided that I wan't going to pull the hand, but attempt to straighten it in situ. My original plan of attack had been to find a piece of transparent rigid polythene tubing (like you get with some scientific aerosols) with a bore just slightly larger than the width of the tip and try to slide it down over it, levering gently as I went.

A real steady hand job ! Luckily the smallest bore tubing I could find was a shade under 1.00mm - which was way too big. :roll:

So I resorted to Plan B - which was to massage the hand between two pieces of pegwood (read a coffee stirrer and cocktail stick):

Getting there. 

January 19, 2014 at 7:32 AM Flag Quote & Reply

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