The static, dynamic and inertial loading characteristics of the slider crank mechanisms were studied and the necessary equations were also deduced. The torques and the loads acting on the crankpin were analytically determined. The static and dynamic loads were analyzed analytically which, results in the load applied to crankpin bearings. When this load was applied to the FEM in ANSYS the boundary conditions were determined according to the engine mounting conditions. The analyses were doing in different engine speeds the results are the critical engine speed and critical region on the crankshafts. Stress variation over the engine cycle and the effect of torsional load in the analysis also investigated. The pressure, which calculated from the engine specification, was used to calculate the load boundary condition in both static and dynamic simulation model, and other simulation inputs were taken from the engine specification Table 3.1. Basically the main objectives of these researches were to modeling, meshing the crankshaft and investigated the static and dynamic characteristics with the help of software. The results of all stresses were shown by the static and dynamic structural analysis in the methods of FEM analysis with the help of ANSYS software. Finally weight optimization was applied using geometric or shape reduction methods. In static load the maximum bending force applied on crank at angle of 180° and 360° and the maximum torsional load developed at an angle of 90° and 270° in one full rotation of cranks. The maximum dynamic loads occurred at crank speed of 1600 rpm and 3200 rpm. The radial force on the connecting rod end (crank pin center) was decrease when the crank speed increase. Similarly in dynamic loads the maximum radial load developed at angle of 360° at first full rotation and 720° at second full rotation of crankshaft and also the maximum tangential load developed at an angle of 270° at first full rotation and at 630° at second full rotation. The optimization resulted in 20.63 % weight reduction of the forged steel crankshaft, which was achieved by changing the dimensions and geometry of the crank webs while maintaining dynamic balance of the crankshaft.