Seiko 7A38 - by the numbers

Those of you who stick purely to collecting Seiko 7Axx's will probably never encounter this little problem. I think I can safely state that all Seiko 7Axx's use tension-fit crystals - i.e. the crystal is held in the watch case / bezel using a nylon gasket which is compressed during fitting. However, there are other brands of watches based on 7Axx movements, that use glued in crystals: for example the Cartier Ferrari Formula Cal. 531's and 532's and quite a few of the dressy Orient J39's.

Therein lies my latest dilemma. I've just received an Orient J39908-70 thanks to help from Italian forum member Fabio (fmc000).

See this thread and a couple of Fabio's photos showing the scratched and chipped crystal:

It obviously needs replacing.

Thing is, I've done one of these before - the very first 'beater' Orient J39908-70 that I got from eBay Australia in August 2011 (the one with the battery acid damaged movement). I pressed out the old crystal 'cold' (unwittingly treating as if it were a tension fit crystal) and it shattered into a million tiny shards. I then spent ages scraping the old glue residue and shards of glass off the inside of the bezel. 

So there's gotta be a better way of removing a glued in crystal, right ? 

Well, according to Esslinger's ever-helpful website there are three ways:

http://www.esslinger.com/howtoremoveagluedcrystalwithhandpressure.aspx

http://www.esslinger.com/howtoremoveacrystalwithheat.aspx

http://www.esslinger.com/howtoremovegluedcrystalwithchemicals.aspx

Thing is, I'm a bit wary about using heat or chemicals on this particular watch case, because not only does it have a glued-in crystal ....

But it's also one of those (thin) metal skinned resin watch cases. Hmm. 

More on the subject here:

http://groups.google.com/forum/#!topic/alt.horology/n7k_MfoRYrg

http://mb.nawcc.org/showthread.php?46814-Removing-dried-crystal-glue

Anyway, before I go pressing out that scratched crystal I need to find something that fits better and looks closer to the original crystal.

According to Boley.de's database (if that information is to be trusted) the Orient part number for the J39908-70's crystal is 16-4085C.

http://www.boley.de/en/case-parts/orient?x=9&y=9&search=J39

At least there's no crystal gasket shown against the J39908-70, so it looks a possibility. Doesn't make it any easier to find though. 

I couldn't remember exactly what I'd used before, so I thumbed back through my file of Cousins' invoices around late 2011 ....

and the two Cousins' crystal part numbers I found tied in with what I'd written in this post in the old Orient J39 thread on the RLT forum.

Notice also the crystal is glued in - there's no nylon gasket visible in that photo.

Bit of an odd size too - approximately 31.5mm Ø x 1.27mm thick, with a polished bevel edge.

As you can possibly see from that photo, the crystal has started to shatter around '250' on the Tachy scale.

Sourcing a suitable replacement crystal was just one of the set-backs I encountered which delayed the rebuild.

I pressed out the original crystal, which didn't come out particularly cleanly, leaving glass fragments to clean up.

My first thought was to order a Cousins' 'cheapie' replacement crystal - 31.5mm Ø x 1.30mm thick.

That didn't want to fit, let alone be glued in, so then I ordered another - 31.4mm Ø - which was a bit loose.  

Paul, would this work on  say  a Seiko 7A     Go a couple sizes up on the crystal and glue it in--- instead of using a nylon gasket Have you ever tried it on a 7a ?   I think if your going to glue it in --a little loose will allow the glue to cushion the crystal just like the orig. nylon gasket.   I have glued in many plastic crystals, not trusting the tension to hold.   As the glue is setting up , you have to keep pressure on crystal and keep it centered.  Thats my two cents worth

Of course it would, Don.  Though why anybody would want to go that route bemuses me. 

Dunno if you've ever done one before, but glueing in a mineral glass crystal - and doing it neatly is a tricky job.

I've never done it to a Seiko 7Axx myself - no reason to, but I have done a couple of glued-in replacement crystals on watches for work colleagues - including a fake Tag Heuer Carrera. 

You are right about getting it "neat". Yes I have glued in glass. On some "dress" square Seiko's and mostly on American  Railroad pocket watches.   The trick is to use a good quality two part optically clear epoxy after cleaning everything with acetone. The trick is to get any air pockets out.  But that crystal will not pop out and it's water tight. 

This is what I've used previously (on that fake Tag Heuer Carrera), and assuming it hasn't gone off in the meantime, will be using again on this Orient J39908-70, once I've sourced a more suitable 'correct appearing' replacement crystal:

http://www.cousinsuk.com/catalog/consumables/watch-glass-adhesive/adhesives-uv-ultraviolet-sternkreuz

It comes in a syringe applicator which means you can get a nice even fillet of cement in the crystal recess (and no air bubbles).

The only real 'knack' is finding the correct curing time (dependant upon the strength of your UV lamp / distance from the target). 

Hint: don't pay Cousins or Esslinger's silly prices for UV curing lamps. Look on eBay for a failed home beautician / nail technician.