The high alternating dynamic loads on the crank mechanism set for diesels challenge improve operational reliability connecting rods and crankshafts, which can not be solved without a large complex of scientific research. As the experience of JSC «Volzhsky diesel them. Mama's "study the stress state of the connecting rods in a factory bench tests are expensive, require additional time and cost deadlines constrain the development of serial production of diesel engines. Solve the problem can be analytically using numerical methods of strength of materials, theory of elasticity, finite element. However, this approach is real only if the disposal of researchers of modern computer technology and software, corresponding to the level of complexity of tasks. But even then it prompt decision possible under the condition that the design of the new part of the crank mechanism is not very different from what a mathematical model which is already there. Otherwise, the time and labor costs increase appreciably. So often cheaper and faster to determine the stresses arising in the details, experimental methods - on physical models.