The total frictional loss in a large two-stroke marine diesel engine is rather well determined. However, the contribution (size and distribution) from the different machine elements are not well known. The aim of this study is to establish methods to measure and calculate friction in the piston assembly and guide shoe system for a large two-stroke marine diesel engine. These components are the two major contributors to the total friction in a two-stroke marine diesel engine. The piston pack represents approximately 60% of the total mechanical loss at full load and the guide shoe system 23%. The rest of the mechanical loss is situated in the piston rod 2%, piston skirt 3% and main bearings and connecting rod bearing 12%. Information about the friction distribution can be used in future design of these machine elements. Theoretical models for determination of frictional losses for both aforementioned bearing types are presented. Experiments revealing the size and distribution frictional loss are carried out. The results of the friction measurements are used for verification of theoretical models. This requires additional information such as oil film thickness, pressure and temperature. These parameters are measured and compared with simulations. Studies concerning reduction of the overall frictional loss for both bearings are carried out.