The article presents the model of the crankshaft taking into account the coupling of bending and torsional vibrations. In engineering practice the simplification which is omitting this phenomenon is commonly used. Authors using more complicated model show the influence of bending torsional coupling on the frequency structure of the crank system.At the beginning of the article the problem of vibrations in combustion engine is generally discussed. Then there is presented the analysis of forces distribution in a crank system with the assumption that there is no friction in bearing nodes. Further chapters present two approaches to modeling torsional and bending vibrations in crank systems and indicate the application area of the proposed methodology. In the last but one chapter there were discussed the results of numerical simulations of the proposed model of the crank system. The whole was summarized with synthetic conclusions and plans regarding further research.