Torsion damper comprising: - a disc rotating about an axis of revolution and provided with at least one housing opening delimited by walls including an interior wall (42.2) facing radially towards the outside, a concave exterior wall (42.1) facing radially towards the inside and towards the interior wall and two end walls, these respectively being a direct and a backwards end wall (42.3, 42.4) extending radially between the interior wall (42.2) and the exterior wall (42.1), - at least one main spring housed in the opening, the main spring comprising two end portions each including an end turn (16.1, 16.2) and an intermediate portion comprising one or more intermediate turns (16.3) and situated between the end portions, and - at least one guide washer (20, 22) rotating about the axis of revolution with respect to the disc on each side of a median reference angular position in a direct direction as far as an end-of-direct-travel position and a backwards direction as far as an end-of-backwards-travel position, the guide washer (20, 22) being provided with at least one direct abutment face (34.1) and with a backwards abutment face (34.2) which faces are arranged in such a way that when the guide washer (20, 22) moves away from the median reference position in the direct direction, the main spring is compressed between the backwards abutment face (34.1) and the walls (42.1, 42.2, 42.3, 42.4) of the opening, and when the guide washer (20, 22) moves away from the median reference position in the backwards direction, the main spring is compressed between the direct abutment face (34.1) and the walls (42.1, 42.2, 42.3, 42.4) of the opening, the said torsion damper being such that: - in the end-of-direct-travel position, the direct end wall (42.3) of the opening is parallel to the backwards abutment face (34.2) and the main spring is unbent and bears against the backwards abutment face (34.2) and against the direct end wall (42.3) of the opening, the said torsion damper being characterized in that: - the main spring is a coil spring which is straight when unloaded, - when stationary, in the median reference position in the absence of torque, at least one of the intermediate turns (16.3) of the main spring bears radially against the interior wall (42.2) and the main spring is bent about the axis of revolution. - a disc rotating about an axis of revolution and provided with at least one housing opening delimited by walls including an interior wall (42.2) facing radially towards the outside, a concave exterior wall (42.1) facing radially towards the inside and towards the interior wall and two end walls, these respectively being a direct and a backwards end wall (42.3, 42.4) extending radially between the interior wall (42.2) and the exterior wall (42.1), - at least one main spring housed in the opening, the main spring comprising two end portions each including an end turn (16.1, 16.2) and an intermediate portion comprising one or more intermediate turns (16.3) and situated between the end portions, and - at least one guide washer (20, 22) rotating about the axis of revolution with respect to the disc on each side of a median reference angular position in a direct direction as far as an end-of-direct-travel position and a backwards direction as far as an end-of-backwards-travel position, the guide washer (20, 22) being provided with at least one direct abutment face (34.1) and with a backwards abutment face (34.2) which faces are arranged in such a way that when the guide washer (20, 22) moves away from the median reference position in the direct direction, the main spring is compressed between the backwards abutment face (34.1) and the walls (42.1, 42.2, 42.3, 42.4) of the opening, and when the guide washer (20, 22) moves away from the median reference position in the backwards direction, the main spring is compressed between the direct abutment face (34.1) and the walls (42.1, 42.2, 42.3, 42.4) of the opening, the said torsion damper being such that: - in the end-of-direct-travel position, the direct end wall (42.3) of the opening is parallel to the backwards abutment face (34.2) and the main spring is unbent and bears against the backwards abutment face (34.2) and against the direct end wall (42.3) of the opening, - the main spring is a coil spring which is straight when unloaded, - when stationary, in the median reference position in the absence of torque, at least one of the intermediate turns (16.3) of the main spring bears radially against the interior wall (42.2) and the main spring is bent about the axis of revolution.