Nonlinear behavior of a multirotor system supported by oil film bearings is investigated theoretically by calculating loci of centers of disks and journals of the system using a time marching method. The oil film force of bearings is obtained by solving the Reynolds equation at each time step by a rapid solution presented previously by the authors. It will be shown that a two-disk/four-bearing rotating system operated under the linear stability limit but above twice the first critical becomes unstable when sufficiently large external shocks, an artificial sinusoidal shock and real seismic waves are given to the system. The effect of misalignment of bearings is also examined closely in this study. Presented at the 47th Annual Meeting in Philadelphia, Pennsylvania May 4–7, 1992