In this paper, there has been conducted the stress analysis of cylinder, piston and engine head of the HATZ 1D81 internal combustion engine. The engine, that is located in the Laboratory for engines and vehicles, will be subjected to higher loads than those for which it was originally designed. The aim of this study was to determine the distribution of stress in the models. At first, it was necessary to create CAD models and then using the finite element method, conduct the stress analysis. CAD models were generated in software Solidworks and the stress analysis was conducted in software Abaqus using the finite element method. One part of data necessary for the analysis was given from the University and other parts of data had to be taken from literature or calculated. The stress analysis had to be done for three angles of crankshaft, 0°, 360° and 372°. Loads and boundary conditions had to be simulated so it could describe the real condition those elements were subjected to. All elements were subjected to pressure from gases inside the cylinder and forces that came from other parts of engine. Places of contact had to be replaced with adequate boundary conditions. Stress analysis that was conducted using the finite element method revealed that the most stressed element was the piston, as we could have expected. Highest values of stress and deformation were at 372 degrees turn of the crankshaft, during which is the highest pressure in the cylinder.