In this work, using finite element method (FEM) the effects of preload factor on the dynamic stability of noncircular two lobe hydrodynamic micropolar lubricated journal bearing based on the linear and nonlinear analytical dynamic models are presented. Assuming that the rotor is solid, the governing Reynolds equations for incompressible lubrication of journal bearing have been modified using micropolar theory. Later, the linear and nonlinear dynamic models, including a certain harmonic disturbances and time dependent trajectory of rotor center are applied to obtain the stability performance of bearing. The 4th order Rung-Kutta method has been used to solve the time dependent equations of rotor motion. Finally, the numerical results for the critical mass parameter and whirl frequency ratio of rotor as the stability characteristics of bearing are evaluated for different values of preload factor and compared together. Results show that the stability performance of two lobe bearing enhances by increasing the amount of bearing noncircularity in terms of the critical mass parameter increase and decrease of the whirl frequency ratio. Also, by comparing two dynamic analysis methods, it is obvious that the results of linear dynamic model are more cautious in different investigated cases. The results of nonlinear dynamic analysis reveal that by increasing the value of preload factor the dynamic response of rotor center involves return to steady state equilibrium position, limit cycle periodic motions and contact between rotor and bearing's shell.