Vintage Omega Seamaster Cosmic watch crystal advice

Hello Omega family,

I love my vintage omega, come on who doesn’t?
Surfing the eBay, I came across a vintage seamaster cosmic. The crystal is completely nackered and will need replacement.
The crystal is 32.95mm. I found a replacement but it’s $435aud and it’s for the day date version (longer cyclops).
My question is this, I found a crystal that an omega replacement but not genuine omega. It has a date cyclops and is 33.07mm. Is the extra that much where it won’t fit or is that close enough to fit well?
This crystal is $34aud so significant price difference.
I work on watches as a hobby so installing it is easy, it’s more about the extra 0.12mm.

Looking forward to any help you can provide.

So you think the minute difference will matter

It's hard to say without the watch in front of me to measure precisely, and even then I'd need to see the crystal It might not just be a matter of diameter, the maybe a different profile that may bring you unstuck.
But my guess ( and it is a guess ) is that with a little very careful fettling you might get away with it.
It comes down to rolling the dice.....do you feel lucky?
If it was me I'd take a punt on it. but I'm a fitter and turner so I'm used to making things fit with precision. I don't know your skill level, so I can't really say how doable it is for you.
Of course there maybe someone who knows for sure and if so don't listen to me, go with their advice.

Those front-loaders have a rebate cut in the tension ring that that dial seats into. GS may have cut this correctly for your watch. If not, it’s sometimes possible to swap the tension rings between crystals.

435aud for an acrylic crystal seems obscene to me. I’m sure you can find cheaper than that.

Bear in mind also that Omega outsourced parts like crystals, so it will still have been made by one of the larger fabricators like Sternkreuz….. or maybe even GS!

Thanks guys, I think I’m going to have a crack at it for its price. I’m pretty good with smaller details so if it takes a little bit of fiddling to get it in, I’m ok with that.

Yeah the price for a genuine is crazy. Most of the other models of omega I could see crystals for at 1/8 the price and all genuine articles. Just with the cosmic it was not.

The other issue with the genuine one is that it had a cyclops for a day/date dial.

Of course it should go without saying that if you can get it in, you would be well advised to get it pressure tested to see if it conforms to whatever specification factory water resistance it might have had, before you risk getting it wet.

Good advice, I have numerous vintage pieces from a variety of brands. I pressure test them but only consider them splash proof regardless of the results.

The only vintage piece I have really pushed to have meet its original rating was my vintage Tudor 7934. It still retains its 100m rating.

I forgot to add photos.

Yes the water shot was after successfully testing.

They is a way you might be able to swing it if it seems pretty close, though it may not be without problems further up the track, given that the original crystal looks to be a poly type in the photo, and a lot of plastics have a fair bit of thermal expansion, you could perhaps chill it to shrink it down a smidgen and whilst that is chilling you heat the watch a little, I don't mean bake it, no you would just put it in the sun, and you wouldn't want to chill the crystal to much either as you don't want to break it because it is too brittle, you would also want to make sure there is low humidity as you will only trap moisture in the watch as it condensates on the crystal, you would need to move quickly before the temperature differential equalises, but not use any force, if it just doesn't all drop into place, stop and try the process again.
What are those aforementioned further problems I hear you ask? Well the potential condensation problem that I've already mentioned is one and the other one is once the temperature has equalised it wont be possible to get a temperature differential of the components you want to separate, so it may well be difficult to pull apart again if and when you might need to in the future, which is why you don't want to apply any force during assembly, it just wants to drop in to place.
This is just me throwing up possible solutions, if anyone knows better for sure then please say so, I won't be offended if you can poke holes in my theory. Indeed please do so.

The temperature difference seems like a decent idea if nothing works. If it ends up seating too tight when the temps regulate, the only thing that will happen will the micro cracks in the crystal will appear and render it ruined. But if that happens, it wasn’t going to fit anyway so no harm no foul.

It’s an idea I didn’t think of. Moisture would be the biggest issue I can think of. But if it doesn’t work I can remove it. Etc.

I wouldn't be relying on the temperature differential to compensate for the full 0.12mm though, maybe from 0.02 to 0.06mm it might get you in
The problem is you won't be able to get a sufficient temperature difference as you can't really heat the watch beyond what it may experience in normal use and you can't exactly use something as brutal as liquid nitrogen to chill the crystal, like I do on the stuff I normally work on.
Liquid nitrogen, dry ice, the induction bearing heater and the oxy torch are my work buddies! but not for watches!

We are talking about 0.1 of a mm here as well. I’m hoping it goes in well. Only one way to find out now I guess. It’s coming from overseas so it will take some time to get out here to Australia. When it does and I have tinkered I’ll post photos of either triumph or failure. That’s way in future, anyone attempting the same thing will know whether or not it will work.

If possible I’d like Archer’s experience and or opinion depending on if he has done the same thing in his time of working on Omega.

I dare say he would have access to genuine parts at a more reasonable price.

Well we're at the start of summer so pick a low humidity sunny day, pop the watch in the sun to warm it and burn off any water vapour that might be lurking in it and give it a go......what can go wrong?........Famous last words!

My air conditioning can dehumidify as well as cool etc. let’s see what happens next

In my experience, by far the worst culprit for moisture ingress on watches like this is via the crown / pendant tube. If the crown is not a recent replacement with supple gaskets then it will not be waterproof. When you have a new crown fitted it will have a very slight grip on the pendant tube which is a good sign that it is sealed. Old crowns with hardened/perished/shrunken gaskets often don’t grip whatsoever or even feel loose on the pendant tube.

My guess (without the case ref - is it a 136.017?) would be a PZ5123.

Gleaves sell a clone without the magnifier for £9.

https://gleave.london/glass-omega-pz5123-steel-ring-xac-330-553-generic/

Other option: buy and gilt “PX” and swap the ring for your white one.

https://www.ebay.co.uk/itm/11442656...kuojgsyswq&var=&widget_ver=artemis&media=COPY

I haven’t received the watch yet it’s still in transit. I’ll be able to make a better assessment when it arrives. I’ll post some pics and comments in here when it does.

I did order the other crystal yesterday and I’d like to see how it goes. It was cheap in comparison and comes with the tension ring. I think the watch comes with the ring too. I’m hoping to use the original ring and the new crystal.