Mechanical WW Mystery Back Case Back Removal

fijidad

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The Stainless steel back says, among other things "Dustproof, Shockproof."

What it doesn't say is "Removal Proof." And this is where I'm stuck...can't get the back (or the crystal) off.

So is this some secret model that was designed just to give future watch mechanics headaches, or what? There is no discernable lip on the back upon which one could work a removal tool. I cleaned up all the gunk that was residing in the crevices, but still no leverage.

Any suggestions would be appreciated. Best, Dan

Benrus.JPG
 

fijidad

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It doesn't open, it comes out the front after removing the crystal. It will have a split stem.
I am unfamiliar with the term "split stem", please explain.

I attempted to remove the crystal with my crystal lift and, after the first unsuccessful attempt, stopped not wanting to do any damage. Is there any special tool that is needed to remove the crystal? Thanks, Dan
 

fijidad

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The crystal is pushed off with compressed air, using a syringe type of thing via the stem tube. A split stem is a two part stem that pops apart- so you just pull on the stem till it comes out, then pump air in.
VERY interesting indeed. I would have never known, so thanks very much for the input. The crown and presumably part of the stem are missing, so I'll have to track those down, but first I'll give it a go with compressed air. Thanks again.
 

viclip

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Can someone provide an indication of the psi level for the compressed air used to pop such crystals?

Thanks !
 

Rick Hufnagel

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I use a plastic tipped syringe from the kids old science kit. Lol. Not the top of the line tool, but perfect for this use.

Get a piece of plastic ziplock bag and poke a small hole in it, place it over the hole in the case and press the syringe over it. Makes a gasket. Then just press the syringe down and it pops right out.

Works for me
 
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karlmansson

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The two-tone appearance of the case makes me wonder. Have you tried turning it? Some older cases are smooth yet have a threaded back. You can use a dedicated rubber suction tool or a case ball to try and turn it. The orientation of the lettering on the caseback makes me unsure it’s a monocoque as well. Usually you would find writing oriented in the same plane as the dial.

But as for popping the crystal off of monocoque watches I can vouch for the syringe method. Usually a 5ml syringe will suffice.

Regards
Karl
 
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4thdimension

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I think this case opens by pushing the crystal down through the case front. The crystal is then removed from the case back by prying it up with a thin blade. You can tell it is one of these cases because there is a slot below the stem post that allows it to push through. The case front is actually friction fit to the crystal and case back. Benrus made a lot of these cases. You can usually open them using just your fingers.-Cort p.s.- you can't turn the case back or remove the crystal with a crystal lift.
 
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Peter John

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I think this case opens by pushing the crystal down through the case front. The crystal is then removed from the case back by prying it up with a thin blade. You can tell it is one of these cases because there is a slot below the stem post that allows it to push through. The case front is actually friction fit to the crystal and case back. Benrus made a lot of these cases. You can usually open them using just your fingers.-Cort p.s.- you can't turn the case back or remove the crystal with a crystal lift.
Yup, that’s it
 

karlmansson

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I think this case opens by pushing the crystal down through the case front. The crystal is then removed from the case back by prying it up with a thin blade. You can tell it is one of these cases because there is a slot below the stem post that allows it to push through. The case front is actually friction fit to the crystal and case back. Benrus made a lot of these cases. You can usually open them using just your fingers.-Cort p.s.- you can't turn the case back or remove the crystal with a crystal lift.
Sorry, I don’t get it... Pushing the crystal down through the case? Wouldn’t that bottom it out against the dial?
 

4thdimension

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Sorry, I don’t get it... Pushing the crystal down through the case? Wouldn’t that bottom it out against the dial?[/QUOTE
When the crystal is pushed out, it is still attached to the case back which contains the movement, split-stem and crown as a single module. The case front is friction fitted over the crystal. Without the crystal the two pieces do not stay together. Simpler to do than explain. They are nice cases though and fairly water tight.-Cort
 
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karlmansson

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When the crystal is pushed out, it is still attached to the case back which contains the movement, split-stem and crown as a single module. The case front is friction fitted over the crystal. Without the crystal the two pieces do not stay together. Simpler to do than explain. They are nice cases though and fairly water tight.-Cort
Aah right, so there is a “sub case” within the circle with the lugs on it?
 

fijidad

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When the crystal is pushed out, it is still attached to the case back which contains the movement, split-stem and crown as a single module. The case front is friction fitted over the crystal. Without the crystal the two pieces do not stay together. Simpler to do than explain. They are nice cases though and fairly water tight.-Cort
So, more specifically, the "push" part of this method is conducted how? Pushing on the crystal...with one's thumb, or some tool? I've tried the thumb method, with no movement at all. Just wondering how much force to use in attempting this method.
 

4thdimension

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I support the lugs with my forefingers and mddle fingers of both hands and push down with both thumbs. You'll get it.-Cort
 

fijidad

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I went to the US Patent Office site and looked up the patent number inscribed on the case back and came up with this:
Patent Images.

Based on these images, this case does, indeed, open from the back, with an inner case. Still working on opening mine.
 

fijidad

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And now, the rest of the story: I put some Sili Kroil around the perimeter of the back of the case and let it sit for several hours. Then I devised a tool made from an aluminum parts container that was just larger than the outside diameter of the stainless steel back, and cut an opening about the size of the stem housing in the case, then pushed the crystal toward the bottom of the container, and out it came. Among the reasons it was not forthcoming was that there was corrosion between the two cases, so the penetrant was the correct move. I've attached several images so hopefully you can more fully understand the sequence of events. Now I have to deal with the part of the split stem that is rusted into the movement...with more penetrant. The balance is good, which is a relief. Take a look...and help me celebrate the revealing of the mystery!
 

fijidad

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And thanks to all who guided me through this...much appreciated. Now I have to source the "other" half of the split stem, and a crown. Any suggestions on that?
 

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