Need help - press drill spring

[rendoman]

Hi all!

I'm searching for good advice about how to install the coil spring in my press drill.
I bought this spring, the internal diameter is 22mm, perfect size for the shaft. The trouble is the external diameter, the round seat for pin prevents the spring from going into place.
The spring has enough force, it's quite hard to turn by hand, it's even difficult to use the left threaded alu case.

I'm thinking to build a sort of frame jig in order to compress the spring and then tie again with wire, but maybe there is a better way

Any advice welcome, thank you for your suggestions