In this study, we have developed a mathematical model, which formed the basis for the development of a digital diagnostic model, for the question of the relation between the engine torque (and therefore power), and the clearances in the basic and secondary bearings of the crankshaft, to diagnose clearance values in these bearings, /which will inevitably affect on the torque and the vibrations of the engine/, where multiple and various grand-scale case experiments were carried out through simulation and arithmetic experimentation on a diagnostic model, which constituted the first and main phase (the instruction phase) of the full diagnosis. And at the end we discussed the results and put some conclusions and recommendations to complete the work in the future.