A simple model from first principles has been developed to estimate the heat transferred from the piston rings and skirt to the cylinder wall. The model considers the various forms in which heat is transferred from the combustion gases to the containing walls, namely, convection and radiation between the gases and wall surface, and conduction from piston rings and skirt through the oil film. The model also includes frictional heat generation by the rings and skirt as a result of the piston movement. Results presented in this paper show that the heat flux predicted by the model on the thrust side of the bore, at an engine speed of 4000 rpm and engine load of 100% of the limiting torque, was generally of the same order of magnitude as the heat flux estimated from experimental measurements. They also demonstrated that in the process of heat transfer from combustion gases to the cylinder wall, convection and radiation of heat have their greatest influence on the total heat flux in the top section of the cylinder bore and provide a contribution of approximately 25% over the rest of the stroke. However, the distribution of heat flux in the middle and bottom parts of the stroke shows that the main mechanism of heat transfer is conduction from the piston assembly.