A tiltrotor aircraft may be provided and may include a mast assembly, in which the mast assembly may include a mast; a bearing system; a housing; and a housing cap secured to the housing, wherein the bearing system is between the mast and the housing. The bearing system may further include a first bearing assembly including a first inner race, a first outer race, and a plurality of first tapered roller bearings; a second bearing assembly including a second inner race, a second outer race, and a plurality of second tapered roller bearings; an inner spacer and an outer spacer in which the inner and outer spacers are between the first and second bearing assemblies; and a retaining device in which the retaining device and the housing cap provide, at least in part, pre-loading for the first and second bearing assemblies.