hadrien_dugas, I figured it out, change the state of the outer tube to no collision, it will work like you want.
I drew two concentric tubes and grouped then individually. I then connected a motor to the outer tube. When I ran the simulation I had the same problem, as you, the outer tube rotated but moved up until the bottom inside surface came in contact with the inner tube, outer surface. So thinking like a logical person, I tried to make a "bearing" on the end opposite the motor, then grouped the bearing with the outer tube, with the inner tube running through it. I then started thinking about what was happening. I tried static state for the outer tube, well of course it didn't move at all. I changed the SP properties shape to sphere, no change.
I found the no collision state and changed the state of the outer tube to no collision voila' it worked. Video to follow (as soon a get time)