In the present study is shown how to change the main indicators of torsional vibrations of crankshaft, in case of changing its masses. In the study it was taken the crankshaft of diesel engine with 4 cylinders in line with 5 main journals. Previously the crankshaft was without counterbalance , and later there are added four counterbalances, to eliminate the large and no homogeneous consumption of his intermediate journals. For this crankshaft, it was performed the study of free torsional vibration of the crankshaft system, for both cases. To study the torsional vibration of the crankshaft system, the first it is carried the construction of equivalent reduced scheme with five discs connected to four flexible shafts . Reduced inertia moments of disks are determined for each crank of crankshaft, for case without and with counterbalances, by received and the impact of group connected rode and piston mass. Results show that the reduced inertia moments of disks for the case with counterbalances grow to 24% . Reduced rigidities of crank are determined by theoretical methods through empirical formulas Zullcer Zimanjeko, recommended to the tractor engines At the end, it is calculated free frequency and vibration forms, using Tole-Holxer method. From calculations, it results that the frequencies are 10% smaller, while the vibration form varies slightly. Most charge part in torsion is shaft 5. In this case that first frequency to be in the area of revolutions of engine and the level of torsional vibration can worsen, therefore it should check the resonance areas and vibration amplitudes.