The register mechanism of the Buffet Crampon 1180 Bass clarinet

The register mechanism of the Buffet Crampon 1180 bass clarinet is completely different from any other. I don't understand why. It is not easy to understand and when a wrong part is used, as in my case, it is impossible to get it work well. But I figured it out.

The mechanism is shown in the figure below.

A is the register lever. It pushes up part C that holds a rocker that can open both the registers keys E and D and when things work well only one of them depending on the use of the upper Bb key.

The first thing you have to do is to adjust the spring under register key E at position H.
The spring must just be able to open key E when the register lever A is used.

The strang part is the flat spring in position G.

It is very important that this spring has the right strength.
I once had the issue that a 0.4mm spring was mounted. It would not work.
The original spring is aa blue steel 0.25mm. Any other size won;t work.
You can order them from Buffet Crampon of course but there service speed is not at a nice level.

You have to adjust the tension of the spring so that the tip always toughes the arm F connected to an intermediate connection F to the upper Bb key.

By the way the connection F is provided with a needle spring. It is hard to figure out why that spring is there! The reason could be to prevent metal ticks when the Bb key is released. 

On top of the arm G there is a little adjustment screw. When you are lucky it still works.
I sometimes remove it and replace it with a M2.5 nylon screw after tapping new thread in the hole.

The screw can be used to prevent E from opening when D is open.

So finally the E nd D keys can both be opened but never at the same time and switch when the upper Bb key is used in combination with the register lever.