Crystal with Nylon Gasket - what is the trick ?

[Garfield]

Does anyone have any tips how to get a crystal to fit into a bezel where a nylon 'seal' is present - this is on a Seiko 7A38. The crystals I'm buying are MSM Sternkreuz 31.0, I have the correct crystal gaskets 8617.9152 - I have yet to get one of these crystals installed successfully, I really struggle to get them to start square. When I have got them to start square the crystal gasket has deformed and prevents the crystal seating so again the crystal isn't square.

I've broken a couple of crystals now and destroyed one gasket, I have tried to lubricate with soap solution, I have just ordered 3 more crystals but two of them I went down to a 30.9mm instead of 31.

Any tips for installing this kind of crystal - first crystals I've really broken and I've put some pretty thin ones in my pocket watches - I don't like breaking things so I must be doing something wrong.

 

[praezis]

What is essential?
- a quality press (upper/lower insert in one line, not tilted)
- the right size gasket
- the right size crystal

Crystal + gasket must be 0.1 mm bigger than the case opening.
E.g.: Sternkreuz gaskets are 0.35mm thick. A 31.0 mm crystal plus 2x 0.35mm gasket = 31.7 mm
This will fit a 31.6 mm case opening.

Frank

 

[Al J]

Few things to keep in mind when setting crystals of this type...

The crystal gasket goes in the case first, and often (depending on the brand/type) there will be a chamfer on the gasket that helps the crystal get started:

You need a good press, with dies that line up properly - for thicker dive watch crystals a good quality rack press works well:

Don't press too hard or too fast - gentle pressure, and rotating the case under the top die can help, so press a little, then rotate, then press, then rotate - this can help work the crystal in without damaging the gasket.

When the crystal is fully seated, you aren't done yet. Often the gasket will push the crystal back up over time, so I always let the case sit for 20 to 30 minutes, then go back and seat it again. You will often hear a distinct click when the case seats the second time, like this:



Once you are done check the crystal from the inside of the case to make sure there is zero gap, so you don't want this:

You want this:

Always have spare gaskets on hand, because even with the best equipment you can sometimes get it lined up wrong, and once the gasket in pinched, it's garbage.

Trying to do this with a cheap press is going to be very difficult.

Hope this helps.

Cheers, Al

 

[Garfield]

There's a common theme here - decent press and dies, thought mine was - clearly not decent enough so I've invested in a present to self - a rack type press - more tools to add to the clutter of essential but little used.

 

[Al J]

I just pressure tested a dive watch yesterday and it failed in the machine - the crystal had popped right out of the old seal. I could put the crystal back in with my fingers, so I have a new seal on the way. I didn't remove the crystal during service, so it appears that someone else has used the old seal over again, and it's not the first time this has happened on a watch I've serviced.

Passed the vacuum test, but failed the pressure test as the crystal had popped out:

These seals are meant to be one time use only.

Cheers, Al

 

[Al J]

Did you put a new crystal in before putting it on the tester?

No, as I said in the post above I didn't remove the crystal during the service.

 

[Al J]

Ah. Well it is something I have never seen happen on any watch I've pressure tested..

As I said, this is not the first time I've had this happen - here's another one from a few years ago:

Oddly enough it had just gone through the leak finder program, and said that it was okay to be checked in water. Before the chamber opened, I heard the pop, and the crystal had come right out as you see above.

We all have our own risk tolerance I guess, but for me I won't use these gaskets over again - if the crystal is removed during the service, I always replace the gasket.

Cheers, Al

 

[Al J]

I only used the old seals on Citizen because there was too high a failure rate attempting to use the provided new seal. Even though I have the Citizen press.
I have had issues with Omega seals. Which is why I purchased a box of them.

What issues did you have?

 

[Garfield]

Just shows how appearence can bite you, looks fine but looks are deceiving. I need to study the process of testing a watch - if you pull a vacuum and the case is sealed then the air is going some place - so I'm not surprised if the crystal blows out - same too if you pressurise the case then equalise it suddenly - I've always wondered how the testing works without destroying an expensive dive watch.

I have new crystals and gaskets, ordered a new press but I doubt it will arrive before the new year.