A mechanism (1) comprising a driving element (4) for rotationally driving a winding shaft (2) for a closing or sun-protection installation of an opening (0) and at least one spring (5) for compensating a weight of the installation. The spring (5) is mounted around the driving element (4) and is jointly associated with a sub-unit (10), which can be at least partially introduced in a unitary manner inside the shaft (2). The spring (5) includes a first end (51) kinematically linked to said driving element (4) so that the first end (51) is immobilized in rotation abut an axis of rotation (X-X′) of the shaft (2), and a second end (52) kinematically linked to the shaft (2) when the sub-unit (10) is placed inside the shaft (2) so that the second end (52) rotates about the axis of rotation (X-X′).