Gruen case back removal - snap or screw?

[rjenkinsgb]

Hi all,

I've just received this after a long time in transit. It tries to run, but obviously needs a service.

OK, open it up .... But how?

It's a plain round back, very thin edges, with no sign of a grooved area anywhere for a case knife. It also looks like someone has been trying to pry it and slipped a few times.

Is this a snap on type or a screw on that needs a friction drive to turn it?

 

[RichardHarris123]

I don't know but I suspect it's a snap back, nothing to get a grip on for a screwed back.  Try the nut method, if it's not a screwed back, it won't do any damage and you could insert a bolt and pull on that. 

[ManSkirtBrew]

I just finished servicing this exact watch, and it is definitely a pry off. The divot for your case knife is hard to find, but it's definitely there. Look under good light with strong magnification.

The movement will most likely stay in the caseback, as it's kind of a tub. Let me look around and see if I have better pictures of the caseback for you.

No luck on better photos. If you're still stuck later, I can take pictures when I get home. Good luck!

Edited May 22, 2024 by ManSkirtBrew

[RichardHarris123]

Haha, posting at the same time. 

[rjenkinsgb]

Thanks guys, you are spot on correct - the notch is minuscule & I could only see it with magnification.

It's so small I had to use a sharp knife tip rather than a case knife. Oddly enough, it's at the end of one of the clusters of scratches!

I was slightly concerned when I took the strap off and saw "Hong Kong" stamped on the edge of the case - but's it's all OK.

 

I now [hopefully] have two good N510 movements, this sub second and one I posted previously with centre seconds; and both have rather tatty cases. The other is a somewhat similar that was once chrome & I was considering trying to nickel plate that, but in the meantime saw a listing for a supposedly NOS Gruen 510 case.

I got that as well, it's the one on the left below. "Vacuum" marked, octagonal recess screw back printed Gruen Guild, with a machined movement ring. I suspect it needs a special dial to suit, as the internal diameter is somewhat smaller than either of the dials on the movements I have (~28.3mm).

 

.... I got distracted/carried away and stripped the movement before I posted the above part! It all looks good, the only point with any visible wear is under the crown wheel edge. There is a tiny nick on an edge of the train bridge, but other wise excellent.

 

[rjenkinsgb]

I'm having difficulty finding an exact match to the spare case & what movement it originally had?

The nearest I can find are the Power Glide, with a 560RSS movement and Borgel case - though that model has a deep case back for the automatic works, while my case has a flush back.

https://gruen.watch/?product=gruen-geneve-23-precision-power-glide-560rss

https://www.birthyearwatches.com/product/c1959-gruen-power-glide-automatic/

The case shape and crown detail are identical to that, and dimensions match except for depth.

 

The 560 appears to be the same diameter as the 510 and from the same era, so it does seem possible that it's for a less common 510 version? I just have to find an appropriate dial to suit it.