Seiko 7A38 - by the numbers



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Forum Home > Parts Info, Tech Tips and Tinkering > Crystal for a 7A48-5000

Rob Benham
Posts: 269

Arrived from the quickest dispatcher in ebay history I should think. 

Didn't expect much for 55 quid but when I opened it, it was like new-ish.  All pushers were filled with impacted dirt but only one switch needed cleaning.  But there's always a however . . .

 . . . or two.  The band is doable, but only in the workshop I had.  Living in penury I'm back to very basic engineering and hand filing a link out of SS plate and then forming it is a bit beyond my scope.

The other issue is the unique? way the crystal is fitted.  Had me fooled. I can't see a seal at all.

I have read through this site's old discussion about the model and taken note of the Seiko, Cousin's and Sternkreuz numbers.  I have to confess, if the dome was VERY slight, I might have missed it, but I'm fairly sure it was flat.  The bevel was raised above the Bezel, so by about .5mm or less.

I note that there are crystals with seals combined.  This would make sense.  It would make a lot more sense if such a seal went down as far as the thread-like rings below, but to get that height it sits on a ridge just above.  Puzzling, to say the least.

Anyone know if the lens - 315W22GN00 - has a seal?

The vendor did send a spare he mentioned in the ad.  .65mm thik and very scratched.  Nowt so queer as folk.

October 21, 2017 at 7:29 PM Flag Quote & Reply

Site Owner
Posts: 12380


Going by your description, I presume this is the eBay auction for a 7A48-5000 that you won recently.

Though it's not easy to see clearly in the seller's photos, this watch appears to be fitted with a flat round crystal with a small bevelled edge (not slightly domed - you may be confusing it with another 7A48 model), retained by a clear nylon crystal gasket. Which is exactly as it should be.

The Seiko part number for the crystal is 310W62GN00 and the clear nylon gasket (should you need to replace it) is p/n 86179152. That crystal measures 31.0mm Ø by approx 1.5mm thick. I'd recommend you replace it with a Cousins 'cheapie' p/n F150CMH310 or Sternkreuz MSM310 (the latter doesn't have a bevelled edge).

October 21, 2017 at 8:30 PM Flag Quote & Reply

Rob Benham
Posts: 269

Thanks, Paul.  The above numbers are slightly different (one digit each) to the blog from the past.  That may however not have been a 7A48-5000.

I find I have another 7A48-5000 which I paid way over the top for without a band.  I was under the impression they were highly sought after but reading your blog noted you and the members were not that excited about them. :(

It too has a scratched crystal which is flat and less than 1.5mm I'd think.  Still, I feel more confident now, not least of all because of your input. 

With my desk tidy and a spotlight in my Anglepoise, I see there IS a seal in there. Small and clear plastic. 

It appears to have an L section (may have been caused by crush) so that a very small part of it will lie under the crystal - contained within the inner bevel I hope as I'm inclined to use existing seals where I can get away with it.  I had a miserable time with new ones in the US.  $11 each and ruined the first one.  We'll see.

Talking of difficulty in fettling the seals, when I popped the inner bezel off, there was a residue of fluid! Nothing like a bit of oil to make things slip on . . . and off.  There was enough to have bubbles in it.  No sign of it on the movement thank goodness.

I'm not sure whether to remove the crystal gasket and apply it on the glass with the lip underneath.  I can't heat the brass with it in there. 

Both an Esslinger and Sternkreuz offering I have here are both marked 31.0/310 but both show a tad over 31.08  The surface of the seal offers 30.9 or somesuch. 

On the Pilot's forum we are finding Photobucket is rejecting our photos without full fees.  I see your site requesting the URL so I'll have to find a way of overcoming that.  Yes, a picture is worth a thousand words and despite getting a load of kit to extend my old Nikon, my phone is turning out much better pictures.
They're not as good as the cameras used by you and some other members, but not at all bad.

October 22, 2017 at 12:20 PM Flag Quote & Reply

Rob Benham
Posts: 269

Well, this was via the Bucket.  Time will tell.  One can't see the surface of the surround but the extended case was burnished to what I thought was a nice compromise.  The sides are polished bright. 

Having quite a bit of trouble with PB, but at least it's working - eventually.  

Case came up quite well, and the new crystal is in.  Certainly having the brass ring under a spotlight - 1" away - heated it well.

October 23, 2017 at 8:00 PM Flag Quote & Reply

Rob Benham
Posts: 269

7A48-5000 #4 arrived okay and was a pleasant surprise. The tainting of the dial seemed much better than the picture.  However, the band was one devil of a job to get off.  The spring bars, while being nice and thick were unbelievably tight. 

I'd noticed in the ad that there was a twist in the early part of the 6o'clock end band.  Easy?  NOT.  Any pressure on the early links would lead to the disaster simmilar to the one on the band mentioned earlier.  I feel sure that's how it got broken. 

Back to that one for a moment.  The band was strong with the small connecting link in place, but that was the probelm.  The tiny tab holding it in had vanished and that stops the link from easing out and unhooking from the chain.

I sent it to a pal that makes jewlery.  He welded it on argon arc kit which looks at the work through a binocular microscope. Nice.  Waaaaay out of my price range.  But also, the bar of gold was bent.  It's steel with gold perhaps rolled onto the face surface.  He could think of no other way to repair it than to use a rod of pure gold.  Good job he was a good pal. 

Back to the current one.  After a lifetime of getting mechanical things to fit, I could find no way to make the band fit easily onto the watch case.  The first link (the gold bar) was pressed hard against the watch case forcing it down into a greater curve than I'd ever seen.  Not suitable on a large wrist.  Even using skinny spring bars would only ease the situation sligtly.  Nowhere could I grip the ends without risking another ripping of the spot welds, though altering one side at a time allowed gripping on the other side.  It was very, very difficult to get them the same.  Finally in desparation, I milled a bit of the case off bringing the first gold bar nearer the holes by a few thou'.  Better, but what a crazy situation. 

Have any other memebers noticed this restrictive fit of B1406 bands onto this case?

The curvature.

March 19, 2018 at 1:29 PM Flag Quote & Reply

Rob Benham
Posts: 269

A better picture of the twist in the band. 

March 19, 2018 at 1:40 PM Flag Quote & Reply

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