An assembly includes a first structure, a first bearing assembly, and a second structure. The first structure has a first predetermined stiffness, and the first bearing assembly is mounted on the first structure. The second structure, which has a second predetermined stiffness, is mounted on the first bearing assembly, whereby relative motion about a first rotational axis is allowed between the first and second structure. At least one of the first structure and the second structure distort when a force is supplied thereto along the first rotational axis, and the distortion of at least one of the first structure and the second structure imparts a first preload force on the first bearing assembly.