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Discussion Starter #1 (Edited)
Hi All,

I intend to replace the mineral glass watch crystal (which is broken to pieces) on this old Seiko (7009-3119). The thickness is 1.25mm, but how do you properly size the diameter for pressure fitting tolerances ?
With the calipers I measure 29.4mm. Should I get a 29.5mm crystal ? Do you size it 0.1mm over ?

Then I am reading --> here 29.2mm and I get confused. Is this the manufacturer's recommendation ?

SOLUTION:
This model has a removable gold-plated coined bezel. The bezel has a plastic o_ring on the outside that pressure fits to the case. The bezel also has a hard to see plastic o_ring on the inside (in a groove) where the crystal sits and it is pressure fit with the crystal. The correct sizing for the crystal is 29.5mm diam and 1.2mm thickness.
 

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Discussion Starter #6
Or + 0.2 if it is a plastic friction fit and you order from cousinsuk.


Sent from my iPhone using Tapatalk Pro
On my Seiko 5 the crystal is bare fitted against the metal bezel; there is no plastic gasket between them.
There is a plastic gasket fitting the bezel to the case (since the bezel itself is removable).

BTW, I am ordering the crystal from Esslinger.
 

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Hi All,

I intend to replace the watch crystal (which is broken to pieces) on this old Seiko (7009-3119). The thickness is 1.25mm, but how do you properly size the diameter for pressure fitting tolerances ?
With the calipers I measure 29.4mm. Should I get a 29.5mm crystal ? Do you size it 0.1mm over ?

Then I am reading --> here 29.2mm and I get confused. Is this the manufacturer's recommendation ?
In my experience, Seiko crystals are sized in steps of .5 mm. 29.5 would be the correct diameter. Someone mentioned glue. There are some Seiko models where the crystal, assuming it is glass, is cemented directly into the bezel with epoxy. This does not appear to be the case in this instance. Seiko uses either a gasket or epoxy, never both.

For general knowledge, the only plastic crystals that are correctly glued are the fancy shapes, never the rounds. Plastic crystals with internal metal rings (tension ring crystal) are pressed in which a 0.1 interference fit. Plastic rounds without the tension ring, usually known as waterproof or WP, are fitted with either a tool or press fixturing the constricts the outside diameter sufficiently to make the crystal enter the bezel opening and the released to expand tightly into the opening. These two types are not interchangeable. The T-ring crystal fits a case with a straight bezel wall, the WP fits a case with a tapered bezel wall.

James Sadilek -- ccwatchmaker
 

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Normally i try and find the GS cross reference number if i can but there does not seem to be one. I dont believe this has a tension ring but if it does then it will need to be pressed in and i usually get better results on -.1/.2 crystal. if there is no tension ring i go +.2. And use the jaw type crystal remover. OEM crystals go by .5 so makes sense that it was a 29.4 most likely a replacement. I go a bit less because when using a press its spreads out the crystal a bit while pressing and it will not get in and in some cases tension ring falls out. Not the best solution if you’re worried about water resistance but you could always buy a nice glass crystal and get the 29.5 size.
 

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The OP will really have to do that in this case seeing as that model was a flat Hardlex (mineral) crystal from new.
that is the best option, i hate when i see 6139’s with domed plastic crystals when the original was a flat hardlex. I also get a replacement from Spencer Klein but doubt he has one for this Seiko.
 

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Discussion Starter #11
Thanks all the comments and ideas !

Here is what it really looks like. It's a gold-plated bezel that comes off. There is a white plastic O-ring between the bezel and the watch case. The glass crystal itself was flat and had no O-ring at all (there was nothing between the crystal and the bezel). Should I use some type of bonding compound there ?

I am am getting this crystal for replacement (29.5mm flat mineral glass 1.2mm thick from --> Esslinger). It's a 6009A movement and I didn't want the crystal to be more expensive than the insides:) Do you think I should consider something else ?

Gwlrfy.jpg
 

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what are you using to install the crystal? If it is a plastic crystal then you need to get a 29.7 And need to get the jaw type crystal remover. There is instructions right on Esslinger on how to use it to install a crystal. It compresses the crystals so it’ll fit then when you release the jaws the crystal expands Making it tight in the case. If you don’t plan on doing it this way and you just want a ham and egg it by gluing a crystal in then get a 29.4 and the $2 bottle of super new glue, but If you do it this way then I would make sure that watch doesn’t go anywhere near water. Even though their is a bezel gasket.
 

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The original Crystal was flat mineral glass.
Should I heat the bezel with a heat-gun to expand it and then fit the crystal ?
No, just clean all the old glue and bits out (make sure it's ALL gone) and glue the new one in.

UV setting epoxy is ideal - a UV lamp is convenient but sunlight will set it just fine - or you can use "normal" 2-part epoxy but that tends to get a bit messier because most off-the-shelf versions are quite viscous.
 

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Discussion Starter #16
Under the microscope, I discovered there was plastic O-ring inside a groove where the crystal sits. This means it was pressure fit.

The crystal is now in. Thanks to all for your help !
20200107_183351_HDR.jpg
 
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