The following paper points out the use of finite elements method calculation in planning internal combustion engines. The crankcase is analyzed in such a way as to separate the thermal strain from the mechanical strain. Such analysis shows how liner deformation can be partly controlled and how much it conditions clearances generating slap noise between piston and liner. The problem of coupling shaft and crankcase in one single dynamic system shows the interaction between the two members and evaluates with greater accuracy the consequent crankcase wall vibration. An experimental check concludes the analysis.