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Benrus - Open Through Crystal - Waterproofing?


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Hello all. Again, I'm a novice and new vintage watch collector. I've acquired a few Benrus watches, several of which are the "Open through crystal" models. I understand they are one-piece cases, how to open them, and have bought a crystal lift, and ordered some NOS Benrus crystals. But before I open them up I prefer to understand how to do everything once I'm in there. So...with respect to being "waterproof", does anyone know what needs to be done (if anything) to ensure the watch is waterproof? Do  the crystals seat themselves tight enough to be waterproof? Is any type of gasket or sealant used on the outer circumference of the crystal? And what about the two-piece crowns? Are there any gaskets there?

For reference, I have Benrus watches series 3021 and 7001.

Thank you in advance, David

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Those case #'s are from the 3rd and final iteration of the Benrus waterproof design. They had some other case designs in their final years as the quartz crisis came on, but by that time US legal restrictions made them change to advertising only as water "resistant.":

There is no gasket, glue, sealant, crystal ring or separate bezel, just a tight fitting flexible crystal meant to fit the machined groove on the case and be installed (and removed) from the front with a crystal lift or wrench.  There is a gasket in the crown. Their waterproof guarantee always included the disclaimer that the case, crystal and crown needed to be intact for this functionality. 

Not sure how these did on a pressure tester, but it was good enough to secure multiple government contracts for a series of military watch models.

Most of the civilian cases cover the joint in the split stem, so you can't manipulate them to slide in and out from the side (as you can with some of the military models), you just have to trust the system and yank on the crown! 

I enjoy working on that era of Benrus watches. Their ETA movements are reasonable to service, they have parts that can still be sourced, and most were tritium lumed so the dials have nice patina without radium burn marks. 

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JJenkins...thank you for the response. I don't believe these models have a bezel that tightens down. The crystal is removed/inserted into the top of the case using a crystal lift/remover, and fits in tightly. Once the crown and crystal are removed, the movement can be removed out the front of the case. 

 

Geotex...thank you very much for your response. Thank you for sharing your knowledge of how the watch parts fit together, and for the tip about the groove in the case, and the washer on the crown. I'll post back on here whenever I can find the time to work on the watches. 

 

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I realized I left out one additional component that could easily be confused as the ring from an armored crystal if you come across one during disassembly. Depending on the movement, some of their watches in this style had what Benrus called a dial frame. These came in gold and silver (toned) and were for specific case/movement combinations. For the series #7001, two movements are listed as requiring the dial frame, the DR (ETA 2370) and EM (ETA 2390). It is also listed as possible for the automatic FE (ETA 2451) but with the caveat "use a dial frame only if it fits easily over the dial".  These rings were the same diameter as the crystal and sat between the crystal and dial inside the case, so they didn't really play a role in waterproofing but were a spacer to secure the dial. 

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JJenkins...thank you for the response. I don't believe these models have a bezel that tightens down. The crystal is removed/inserted into the top of the case using a crystal lift/remover, and fits in tightly. Once the crown and crystal are removed, the movement can be removed out the front of the case. 

 

Geotex...thank you very much for your response. Thank you for sharing your knowledge of how the watch parts fit together, and for the tip about the groove in the case, and the washer on the crown. I'll post back on here whenever I can find the time to work on the watches. 

 

Geotex, thank you for the additional information. Would you be able to share where you were finding this information? Was it online or do you have your own resources? I any case, thank you!

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Benrus Waterproof Case Series Crystal Info.pdfThe manufacturer's info on this era of cases/crystals/stems/crowns is included in the set of repair/replacement parts Benrus sold at the time. I'll attach that insert. There was also a 3-ring notebook style catalog, parts list and instruction manual that was sent out in the 1950's and updated a few times. These come up for sale on eBay every now and then, and if you are truly interested in Benrus it's worth grabbing one or more (to cobble together a complete set). Some of that information has been shared online in various places so you can also do a web search for Benrus-associated pdf files. A few of those manuals sold last week:

https://www.ebay.com/sch/i.html?_nkw=benrus+repair+manual&_sacat=0&LH_Sold=1

Benrus Waterproof Case Series Crystal Info.pdf

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