How tight to screw down a 100m caseback?

[JeremyLaurenson]

I have an Oris BC3 that I have successfully serviced and now I need to get the thing “water resistant” again.

I tightened the caseback down with a bench mount tool but the o ring came squishing out the side.

New I rings in order from cousins, but what is the rule of thumb for tightening these things?

[RichardHarris123]

To start with, I  thought you had a massive case back. Hehe. Was the gasket lubricated? 

[AndyGSi]

I Rings are for crystals, not case backs.

What gasket/o-ring have you ordered and can you post photos.

[JeremyLaurenson]

Yup, the gasket was lubricated with silicon grease, it is flat with an external diameter of 35mm. Its .6mm thick and .8mm wide.

Not at a place to take a pic at the moment.

[JeremyLaurenson]

Here are pics. Obviously I didnt measure the diameter of the ring like this, I measured the case. I did measure the ring thickness and width using the digital calipers.

So this is a flat ring, rubber.

The question is, when my new ones come in, how much torque should I be using to secure the casebook?

[Knebo]

I'm curious about the answers of others, but I'd use the rubber 8-ball and go as tight as I can with it.

I think that would hit the sweet spot between tight enough and being able to open it again in the future...

[AndyGSi]

Is that the same as what came out?

Can you post a photo of the case as I would have expected an O-Ring to sit in a channel for that rating.

If no channel then I'd have expected a flat ring.

[nevenbekriev]

The force/torque of tightening has nothing to do with watertightness. You tighten the back untill it lays on the case firmly. Tightening it more would only tear the thread, but will not get the back closer to the case.  There is space for the O-ring in a groove made specially for it between the back and the case and if the size of the ring is correct and the surfaces of the case and back that form this groove are clean and smooth, then watertightness will be OK.

[JeremyLaurenson]

1 hour ago, AndyGSi said:

Is that the same as what came out?

Can you post a photo of the case as I would have expected an O-Ring to sit in a channel for that rating.

If no channel then I'd have expected a flat ring.

Yup - that is the one that come out.

 

[AndyGSi]

And is there a channel for it to sit in?

[HectorLooi]

I am really confused.

You say the case measures 35mm, yet the oring shown is 40mm.

You say it's a flat oring, yet in your photo it looks like a round oring.