Question re crystal and crown for ref 2490

[Amadeus]

Hello,
I recently acquired this dual signed bubble back. I’m having difficulty sourcing a crystal and crown. Unfortunately I can’t find this case reference number in any Rolex crystal reference chart. Any advice?

[Amadeus]

Correction: the case reference is actually 2940 rather than 2490 and has a second reference number of 4919

[TimeToGo]

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Wow - Serpico y Laino / Very Nice!
I have a couple reference books, let me see what they say.

[TimeToGo]

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Since I am not familiar with the model number, here is what each reference says:
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[TuRo]

That's ∆ brilliant data ✓

[Amadeus]

Excellent! Thanks @TimeToGo
Now on to the other half of the battle: sourcing them...

[TimeToGo]

Originally Posted by Amadeus

Excellent! Thanks @TimeToGo
Now on to the other half of the battle: sourcing them...

Drop R.W.T. a PM.. He specializes in these types of restorations.

Would love to see other pictures of your watch. Whatever you have available.
These are rare.

[Amadeus]

Originally Posted by TimeToGo

Drop R.W.T. a PM.. He specializes in these types of restorations.

Would love to see other pictures of your watch. Whatever you have available.
These are rare.

Will do once I get it serviced

[R.W.T.]

Originally Posted by Amadeus

Correction: the case reference is actually 2940 rather than 2490 and has a second reference number of 4919

No it is NOT a 2940.

Where are you getting your reference numbers from?

4919 is the reference. If the back says 2940 it has been changed.

You won't make any sense out of the crown references. It's long forgotten lore.

That is basically a standard bubble back crown.

Crystal will be trial and error. You have to use aftermarket. If that were me I would get the crown you want.

Get the gaskets sussed and see if the crystal leaked. If it doesn't leak. Polish it. If it does...well...

I hope you have a sympathetic watchmaker or you are happy to not have it waterproof, because it can

be a time consuming process. The size measurements are a close guess that are shown in the R-20 but that is

for Rolex BP crystals and they are long gone...and even if you have the correct ones...a good friend who plays with such things says...you will break 5 to get ONE in that works.

And you could easily get a GS crystal PHD PK LT whatever the right dimensions...and put it in and have it leak like

the titanic.

It's trial and error.

[Amadeus]

Thanks for the info Tommy. I’ve attached a photo of the caseback. As can been seen both reference numbers are stamped on it. I don’t know if the caseback has been replaced but I suspect that a 2940 caseback was used at the factory and stamped with 4919. So I shall assume to use the 4919 specifications. It looks like I’ll likely have to accept a crystal that won’t be waterproof. However considering how scratched the original one is it’ll still be an improvement. Btw is the bezel on these press fitted or cemented in place?

[R.W.T.]

I would say that this is one of those instances where...no 4919 case backs were available and they just added the reference to the 2940 back, on the line.
Same size.
When asked about those things if memory serves Rolex stated..."no one is meant to see in there but our watchmakers."

The back does not look like a later service part to me. That is certainly one of the period engravings of the marque.

It can be water resistant...it's just a bit of a job. The gasket in the crown is lead and has to removed and replaced. I don't see how that EVER worked, honestly. If anyone works on cars...you know that a head gasket gets one torque and you're done. You can't re-use them. There is not enough space in there for rubber too. Often the lead gaskets are corroded...messy stuff. It has to go. That's a little bit of a trick as well. This was all taught to me by George H. Kiser - Certified Rolex Watchmaker. RIP. He was the go to guy in the Southern part of the USA for these watches for decades after Rolex stopped working on them. Rolex Dallas often recommended him to their clients when they would not service watches themselves.

I fit crystals in these, on many of the ones that come in and I water proof every one of them. On RARE occasion...after exhausting every option I have with full disclosure, added a tiny film of clear silicone to the leading edge. After curing it is inert and so minuscule and compressed between the crystal and the rehaute that it would likely never fail. The idea is to keep it from taking on moisture under normal circumstances. It's 70 years old.

If anyone has ever gone diving in a pool with a high platform..that is roughly five meters...to touch the bottom of that pool you are working very hard and it is a lot of pressure. It also takes a bit of effort to reach the surface...no one is going deeper than that without tanks. No one is going in with tanks...and this watch. :-) Properly set up if you fell into to a normal pool or went swimming in the ocean just splashing around...you're not going to have to worry. I've been in the surf in Honolulu in my bubbleback...no issues.

The bezel as I mentioned in my reply is press fit. It is MERELY decorative. On the earlier style 2 piece, steel and gold cases,
the solid gold bezel screwed to the case middle, semi-permanently, with a lead gasket. I think this was just another weak point in the design for them and also more costly from a gold content standpoint. These later 2 tone cases are 2 piece with the mid case being solid stainless with a "false" bezel underneath the gold appliqué. It doesn't NOT come off...or rather there is no necessity of it coming off. You see a LOT of these for sale with no bezel as they were removed for melt. The crystal replacement is not affected by the bezel. It is an expanding type like the earlier ones and expands into the steel rehaute flange.

[Amadeus]

Tommy I appreciate your wealth of knowledge on this. I just noticed "4919" is indeed engraved between the lugs at 12 o'clock. Ideally I prefer the watch made waterproof but the only diving plans I have while wearing it are desk diving. Hopefully my watchmaker can find a proper fitting aftermarket crystal and I can post photos of the finished product soon. Btw after reading about George H Kiser, I realize he was a remarkable watchmaker who is world renowned for his vintage Rolex restoration...what a loss to the community.