Seiko 7A38 - by the numbers

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Forum Home > Parts Info, Tech Tips and Tinkering > Yema N7 / N8 (Spationaute III etc.) specific case-back tool anybody ?

Seiko7A38
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Posts: 10554

I suspect most of us who change their own batteries in Seiko 7Axx's are quite happy (and reasonably competent) with the Jaxa (copy) 3-prong adjustable screw-down case-back opener. If you haven't already got one, then I strongly recommend you do. They can be picked up on eBay for around a Fiver, and once you've done your first couple of battery changes, the thing will have paid for itself - compared to the Fiver a time (minimum) charged by most high street jewellers.


But what about Yema N7's and N8's ? Not so easy. Sometimes you can get them undone with a 'Sticky Ball' - but not always.

Whereas Jaxa tools can be used, the various pins they usually come supplied with aren't the right size for Yema case-backs:




I saw Bry listing variations of his case-back tool on eBay a few months ago: http://www.ebay.co.uk/itm/251255886363




That particular tool is meant for use on Seiko 6119-xxxx case-backs. Yet those watches have 6 rectangular slots around the periphery of the case-back (the same as on Seiko 7Axx's). So I had my doubts about how well such a tool might work. But it did give me an idea.


So I've been talking to Bry, and yesterday gave him the dimensions: 6 pins - 1.85mm diameter on a 24.5mm P.C.D..


Anybody who's recently purchased a Spationaute III interested ? 


April 8, 2013 at 12:58 PM Flag Quote & Reply

Seiko7A38
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Posts: 10554

5 years on from my original post, we may finally have got a step closer. :)

Earlier today, this came up in my saved eBay favourite search notifications:


http://www.ebay.co.uk/itm/253565425362



I notice Bry is also now listing a dozen other variations of his tool for other watches.


I personally now own over two dozen Yema Spationaute III and N8 Flygrafs, plus numerous other various assorted Yema N8 models, like the dressy N81W63 (which springs to mind) that could certainly benefit from such a tool, specifically designed to fit the Yema 6-hole case-back. Hint. ;)


April 16, 2018 at 4:25 PM Flag Quote & Reply

Seiko7A38
Site Owner
Posts: 10554

I suppose I ought to mention that Bry has reduced the price of his 7Axx case-back tool a couple of times: from the original £12.99 (which I thought was a bit steep) to £9.99 and currently on 'Special Offer' for £7.99. ;)


http://www.ebay.co.uk/itm/253565425362


I haven't succumbed and ordered one yet - still quite happy with my old Jaxa. But I'm looking forward to receiving the first sample of Bry's Yema N8 case-back tool.


May 3, 2018 at 9:33 AM Flag Quote & Reply

Seiko7A38
Site Owner
Posts: 10554

Which I received in the post at lunchtime today. :)


First impressions are generally favourable. It does what is says on the packet. Only slight criticism is that the pins could have been a shade thicker (I mic'd them up at 1.78mm ∅, rather than the 1.85mm specified), they don't need to be quite as long and they could do with finishing off better. Wet and Dry paper beckons ....



I quickly tried it out on a N8 Flygraf (the first one that fell to hand, that didn't have a protective sticker on the case-back) - it unscrewed it and tightened it up again, with the watch just held in my palm. Also tried it for size on an L5 (ana-digi) case-back I happened to have lying around (same P.C.D.) - it fitted just the same.



May 5, 2018 at 7:52 AM Flag Quote & Reply

Seiko7A38
Site Owner
Posts: 10554

I'm not sure yet whether Bry plans to 'productize' these Yema specific case-back tools (and list them on eBay like his latest 7A28 / 7A38 tool). But he told me he'd had a drilling template made, so it's a distinct possibility. So if you're interested, I suggest for now that you add a reply to this thread saying so. ;)

May 5, 2018 at 8:58 AM Flag Quote & Reply

Seiko7A38
Site Owner
Posts: 10554

Not all Yema N8 case-backs use the 6-hole design. Some have 6 rectangular slots around the perimeter of the case-back (à la Seiko 7A28 / 7A38, etc.) So I'm going to start compiling a list of the Yema models that I know this tool will specifically fit.


Yema N7:

N71X31, N71X32, N71X33 Dress Chrono's.

N71Z36 and N71Z396 America's Cup.


Yema N8:

N80P76 Spationaute III.

N80A66 and N80A696 Spationaute III 38mm 'reduced'.

N80P896 (a.k.a. N8 OP8 96) 'Pseudo Plongeur'.

N80Q16 Flygraf.

N81W43 Dress Chrono'.

N81W53 Dress Chrono'.

N81W63 Ditto - Breguet Classique lookalike.

N8YX53 Dress Chrono'.


Yema N9:

N90T296 Moon Phase / Calendar


Yema L5:

L5 OQ4 6 Ana-digi Yachtingraf

L5 OQ6 6 Ana-digi Spationaute


May 5, 2018 at 9:02 AM Flag Quote & Reply

Seiko7A38
Site Owner
Posts: 10554

I haven't ground down the pins on Bry's prototype Yema case-back tool yet - for a good reason. ;) Here's what I meant about them being unnecessarily long. Fitted to the case-back of that same N8 Flygraf, there's nearly 2mm of daylight.



I'm thinking along the lines that those pins could be greatly shortened (to less than 1mm), which would allow the nylon body of the tool to actually sit on the case-back. But first I want to fit some larger diameter brass pins. Hence the reason for not shortening them yet - to give me more purchase when I come to pull them out (probably using my Mole grips).


May 12, 2018 at 7:23 AM Flag Quote & Reply

Seiko7A38
Site Owner
Posts: 10554

In the meantime I did relent and buy one of Bry's 7Axx case-back tools. I like the concept, but I'm still not entirely happy with the execution. To me, a round peg in a square hole is just plain wrong. I tried it on a 7A38 case-back. Initially it was a bit ponderous getting all 6 pins to fit at once. So I rotated it a couple of times and like the Yema tool it does work. But the fit could be better. :/




Incidentally, the pins on this 7Axx case-back tool are 2.0mm diameter, compared to the 1.8mm (or in fact less) that Bry used on the prototype Yema tool. It doesn't really inspire confidence though, particularly when you can see half the pin sat outside the rectangular cut out - doing absolutely nothing. I have a niggling urge to replace Bry's round pins with 2.0mm square brass bar. It's going to require a bit of tricky machining to get them to fit in the existing round holes.


You may have noticed that I didn't have a handle fitted on the 7Axx tool. That's because at the time I ordered it, last weekend (as a 'head only'), Bry had run out of stock of handles. I told him not to worry, because in the interim, I'd already found something I considered better quality. :)


May 12, 2018 at 7:58 AM Flag Quote & Reply

Seiko7A38
Site Owner
Posts: 10554

After searching on eBay, without success, I googled 'Knurled Aluminium Handle' and more by luck than judgement, searching on images, found something that fitted the bill (and Bry's tools) almost perfectly. Cheap too. 8)



They're available from here. I ordered them through their UK website (because it said 'IN STOCK'), but they still shipped from Sweden. :roll: The handles arrived in this morning's post. Next week I'll drop by my local fastener store and pick up some M6 brass studding. I've measured the depth of the drilling / tapping in both handles and it's 39mm, rather than the stated 35mm. So two 50mm lengths should suffice.


May 12, 2018 at 8:33 AM Flag Quote & Reply

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