Vibration behavior of a crankshaft in operation is complicated and difficult to simulate because of oil effects on journals, coupled vibration of crankshaft system parts, combustion and inertia acting on the crankshaft. Particularly, the stiffness and damping of oil film vary with crank angles and thus the numerical analysis must deal with nonlinear vibration. This oil film effects also diversify the vibration modes of the crankshat; the vibration modes in an actual operation differs from that in statically experiment modal analysis.This paper describes a new method developed by the author to analyses, predict, and reduce noise and vibration using several techniques including numerical simulation, finite element method, Sommerfeld concept on oil film effects, and modal frequency response. The results of this work, that is, noise order analysis, vibration order analysis and stress analysis, showed a good agreement with respective measurement data, which demonstrates the validity of this new method. This method was then applied to optimizing the dimensions of the crankshaft system to suppress noise and reduce stress. Accordingly, this method has significantly contributed to determining the best mean journal clearance and the best thrust bearing location pecurialy.