Large axial displacement at the edge of a flywheel causes a clutch to fail to disengage in high-speed rotation. To find out the root cause, a numerical procedure is proposed to investigate the vibration source and to understand dynamic behavior of the crank-train system. A simulation of the whole engine system including block, crankshaft, piston, and connecting rod was performed with AVL/Excite. The resulting CAE baseline model had good correlation with measurements. A comprehensive study was conducted for a set of flywheel and crankshaft models with different materials and unbalanced masses. The contribution to flywheel wobbling of each vibration order was carefully investigated, and an optimal design was presented.