Hermle 130-020 "Bim-Bam", plate separation

[Moose]

Hello.

I am needing to re-bush the main and strike barrel arbor pivot holes on a Hermle 130-020 (know as "Big-Bam Strike" I think).  This is one of those with a vertical, free-sprung balance wheel. But this is my first Hermle movement and I need a little bit of guidance please.

The issue I have is that I can't see how to separate the rear plate from the front plate. I have removed all of the nuts and stripped the strike hammers and escapement away, as well as the plate holding the twin barrels in place. But how to get the back plate off and get access to the gear trains for re-bushing is currently a mystery to me. 

Hopefully the photos are fairly self-explanatory, but the blacked posts seem to be riveted into the back plate, so that it won't come off. It may just be that they are on extremely tightly and need to be levered off, but I don't wish to damage anything, if it is something I have missed.

I hope someone can give me a little bit of a steer on this one.

Many thanks in advance.

Edited July 20, 2023 by Moose
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[watchweasol]

Hi Moose I think the last one I did the posts unscrew releasing the plate.

[Moose]

33 minutes ago, watchweasol said:

Hi Moose I think the last one I did the posts unscrew releasing the plate.

Ahh… I had not considered that. I’ll have a look tomorrow and see. Thanks.

[oldhippy]

10 hours ago, watchweasol said:

Hi Moose I think the last one I did the posts unscrew releasing the plate.

watchweasol is correct. These movements are not made with strong brass or hard steel so the wear a lot and the springs are to strong for the metal a bad design. You will find how soft the brass is when you re-bush its like a knife going through butter. 

Edited July 21, 2023 by oldhippy

[Moose]

Thanks, Oldhippy. That’s good to know. I’ll be more careful when reaming etc. 

[oldhippy]

I forgot to mention. From your description it sounds like it is a floating balance. Just clean it in Ronsonol lighter fluid then dry it with your bench blower. at each end of the balance where the wire goes through it should have a jewel, a tiny drop of oil at each end then move the balance up and down a few times so as to lube the wire, I always used a pocket watch oil, but Windels clock oil is fine for the job. Always use that oil for general clock repairs its the best and it is not expensive. Here is a photo of a floating balance I'm hoping it is something like this, if not can you post a photo of it.

 

[RichardHarris123]

I didn't know what a floating balance was, I found this article https://antiquevintageclock.com/2016/04/04/floating-balance-no-longer-floats/

Don't know if it's of use. 

[watchweasol]

Used on quite a lot of 

Hermle clocks. And also Smiths.

[Moose]

Thanks for everyone’s help and tips.

Got it finished today and now just running it for 7 days or so, to gauge the rate and power reserve.

No issues to speak of; the wise words of Oldhippy regarding the softness of the brass plates saved me from being over-aggressive with the reamers!

Oldhippy, I did not lubricate the balance, but after reading your tip, I will go back and do it, as the amplitude seems a little low, although it it is keeping good time.

Edited July 24, 2023 by Moose

[oldhippy]

Nice re-bushing on the barrels. I would certainly oil the balance tips.  I don't see any oil on the escape wheel or the pallet pins.

[Moose]

Thanks Oldhippy. I don't have a purpose made tool, so I had to do it by hand. I have done it a few times previously, but not on such a large hole (6.5mm with a 4mm pivot hole), or on such a soft plate!

I took the balance out again and re-cleaned it and used some clock oil on the jewels/wire, as you suggested.

I was considering a grease on the escape wheel teeth/pallet pins, such as Moebius 9415 (as per watch escape wheels). What do you think, would this be too light for this escapement?

[oldhippy]

I would use oil on every other tooth of the escape wheel it will attach to the pins of the pallets. I know there is hardly any oil sink for the pallet pivots so can only oil the pivots direct. 

[Moose]

Thanks, will do that.

G.

As a matter of interest and not having worked on this type of balance before, what is an acceptable balance amplitude?

I seem to be getting around 260 degrees - or thereabouts - based on a slo-mo video capture. I would regard that as OK given the age of the thing.

[oldhippy]

That is good but after you have gone through what I said you might get a little more. When the rotation is around 20 degrees that is the time to worry which I have seen, but that is before a service. 

[Moose]

All complete now and sitting for a long term test till I give it back. 
Cleaned and lubricated the balance jewels and also lubricated the pallet-pins and teeth.

Now seems to be achieving around 290 degrees amplitude (by eye) and keeping time to within a minute or two over 12 hours. The extended test will give a result over 7 days and I can make further adjustments as required.

Many thanks for all the suggestions for repairing and servicing this interesting (for me) movement.

Photo during re-assembly. New bushes fitted, partial reassembly. Just prior to the barrels being refitted. Then the strike hammers and escapement on the other side.

And a before pic.

Edited July 26, 2023 by Moose

[oldhippy]

The time keeping should be better then that it should be down to seconds per day.

[Moose]

I’m sure it will be better than than that over a longer period, as that was just for the first 12 hours. I had to put in a big adjustment on the balance adjuster to get it to come into reasonable time. I suspect that it had not really been adequately serviced for years, if at all, since it was assembled. So I have not yet had time to measure the going rate over an extended period, as it arrived non-working.

I have high hopes it will settle down well.

Edited July 26, 2023 by Moose

[oldhippy]

I'm sure you will get it right. 

[watchweasol]

Hi Moose   here is some information i have from the Hermle manual regarding the floating balance unit. it might be useful for future reference.   cheers

Herm-1.pdf Herm-2.pdf Herm-3.pdf Herm-4.pdf Herm-5.pdf hermle_floating_bal_summary.pdf