To clarify the mechanism of torsional and lateral bending vibration of the cylinder block which has a large affect on engine noise, an analysis was conducted of the influence of crankshaft torsional vibration on cylinder block vibrations. There were two main results. The first is that the lateral forced vibration of the crankshaft by the fluctuation of the lateral inertia force generated with the torsional vibration of the crankshaft directly causes the vibrations of the cylinder block. The other is that the level of cylinder block vibration varies according to the condition in which the frequency of the fluctuation of inertia force approaches the resonant frequencies of the cylinder block. Further, noise reduction can be achieved by optimizing the resonant frequency of the crankshaft torsional vibration.