High levels of dynamic loads in a modem diesel engine take place at low frequencies and are connected with the forced vibration of the engine under the action of excitation gas and inertia forces. The lower range of these frequencies are equivalent to the speed of the engine (two stroke) and half engine speed (four stroke). They lead to high stress levels and deformations and often cause internal damage or component failure as well as increasing vibration transmitted to the foundation. One of the most important factors in improving the reliability and durability of engine components and reducing the level of vibration is providing sufficient rigidity for the engine housing. Careful choice of the main dimensions and design parameters will greatly influence engine performance. An engineering approach to the Finite Element analysis of low frequency forced vibration is proposed for the elastic system including crankshaft, engine housing, elastic mounting and foundation. This approach is applied to the analysis of medium speed marine diesel engines with particular attention being paid to the analysis of the rigidity of the engine housing. A solution procedure is proposed to define the loads transmitted from the crankshaft to the main bearings. The procedure takes into account the reciprocal influence of elastic and inertial characteristics of the crankshaft and the engine housing mounting on the elastic foundation, alteration of load amplitudes according to the angular position of the crankshaft, and hydrodynamic behaviour of the lubricating oil film in the contact zone.