This paper investigates the influence of friction power loss on the main bearings of an internal combustion engine crankshaft that accounts for the major tribological operating factors: main journal surface roughness, lubrication oil temperature, engine crankshaft speed, journal bearing clearance, and fuel supply advance angle. All these factors have been analyzed in detail for an in-line six-cylinder internal combustion engine. The mathematical model is mainly based on the Reynolds equation, which can be solved using the finite-difference method and the Euler method. The lubrication film contact is calculated based on the Reynolds differential equation via the pressure balance calculated iteratively in the time domain. The results show that friction power loss factors such as main bearing clearance and surface roughness should be considered engineering factors in the engine and component design process.