The moving parts of internal-combustion engines endures the highest and the most complex stresses. The tensile compression, bending and twisting stresses appear under the action of gas pressure forces and inertic forces in the elements of the crankshaft. One to the bending stresses, the crankshaft is the strained compromising the coaxiality of necks and bearing bushes. Taking into account these points (considering the points), the determination of the stresses to witch it is put, becomes a defining element for designing and testing to strength. This work presents a numerical modelling (MathCad program) for determining the stresses to which the moving parts is put for the marine two-stroke engines.