Electric motor of the type comprising: - a casing arranged along a main axis, comprising: a side wall; and first and second end walls, also called first and second flanges, arranged transversely to the main axis - a rotor and a stator forming a rotor-stator assembly, the stator being integral with the casing, - an output shaft integral with the rotor, coaxial with the casing along the main axis, and - a first and a second bearing, configured to keep the output shaft free to rotate with respect to the casing about the main axis, each of the first and second bearings being mounted and second bearings being mounted between the output shaft and, respectively, a first annular cage attached to the first end wall, and a second annular cage attached to the second end wall; the electric motor being characterised in that: it comprises a first, a second, a third and a fourth radial surface; said first, second, third and fourth radial surfaces having the form of rings (37, 38), continuous or fragmented, the first and second radial surfaces being of identical diameters; the third and fourth radial surfaces being of identical diameters; - the second radial surface is supported by the side wall of the housing and the first radial surface is carried by an impeller integral with the output shaft and arranged along the main axis between the rotor and the first annular cage; - the third radial surface is carried by a first outer ring of a deflector integral with the output shaft, said first ring being arranged along the main axis between the rotor and the second bearing; and the fourth radial surface is carried by a second ring of a seal integral with the second end wall of the casing and arranged along the main axis between the rotor and said second bearing, at least one of the third or fourth surface forming a radial projection with respect to the first or second ring bearing said third or fourth surface; - in an operating position of the rotor-stator assembly, the first and second radial surfaces as well as the third and fourth radial surfaces are spaced apart (25, 43) along the main axis; - the output shaft has means (29, 30) for guiding it relative to the casing translationally through a stroke (25, 43) along the main axis; and - the electric motor is configured so that a movement of the output shaft translationally through said stroke (25, 43) along the main axis, guided by said guiding means (29, 30), brings the first and second radial surfaces and the third and fourth radial surfaces into contact with each other, so as to radially retain the rotor relative to the casing. - a casing arranged along a main axis, comprising: a side wall; and first and second end walls, also called first and second flanges, arranged transversely to the main axis - a rotor and a stator forming a rotor-stator assembly, the stator being integral with the casing, - an output shaft integral with the rotor, coaxial with the casing along the main axis, and - a first and a second bearing, configured to keep the output shaft free to rotate with respect to the casing about the main axis, each of the first and second bearings being mounted and second bearings being mounted between the output shaft and, respectively, a first annular cage attached to the first end wall, and a second annular cage attached to the second end wall; the electric motor being characterised in that: it comprises a first, a second, a third and a fourth radial surface; said first, second, third and fourth radial surfaces having the form of rings (37, 38), continuous or fragmented, the first and second radial surfaces being of identical diameters; the third and fourth radial surfaces being of identical diameters; it comprises a first, a second, a third and a fourth radial surface; said first, second, third and fourth radial surfaces having the form of rings (37, 38), continuous or fragmented, the first and second radial surfaces being of identical diameters; the third and fourth radial surfaces being of identical diameters; - the second radial surface is supported by the side wall of the housing and the first radial surface is carried by an impeller integral with the output shaft and arranged along the main axis between the rotor and the first annular cage; - the third radial surface is carried by a first outer ring of a deflector integral with the output shaft, said first ring being arranged along the main axis between the rotor and the second bearing; and the fourth radial surface is carried by a second ring of a seal integral with the second end wall of the casing and arranged along the main axis between the rotor and said second bearing, at least one of the third or fourth surface forming a radial projection with respect to the first or second ring bearing said third or fourth surface; - in an operating position of the rotor-stator assembly, the first and second radial surfaces as well as the third and fourth radial surfaces are spaced apart (25, 43) along the main axis; - the output shaft has means (29, 30) for guiding it relative to the casing translationally through a stroke (25, 43) along the main axis; and - the electric motor