The motor“a depression”, vacuum type of the 7A works by a membrane in leather material inside the motor box.

The membrane has the same shape of the inside surface of the box (box composed by 2 identical shells).
The main operation is to fit a piece of leather (taken from a shoes remaker) to the oval inner profile of the box.
First, a piece of wood has been cut and fit to the oval shape of the inner side of the box. Then, after wetting completely the leather, the leather has been placed between one shell of the box and the wood; then close the box and bolt it with its screws.
After one week so closed, the membrane took the required oval shape.

After taken out the wood and covered the membrane with proper grease, the box with the membrane placed inside, has been closed and the motor ready for working. How to test it and verify if the work is made in the good way? Unfortunately only when the engine is running....after several months, at the end of the restoration....it works properly

At the purchase, the original membrane was still present but broken in some of its corners.

membrane thk 1 mm