Nowadays the challenge in design of auxiliary devices for automotive small engines is focused on packaging reduction and on the increase of the performance. These requirements are in contrast to each other and in order to fulfil the project specifications, new and more refined design tools and procedures need to be developed.This paper presents a calculation loop developed by Pierburg Pump Technology Italy S.p.A. (PPT). It supports the design of a variable displacement oil pump component for engine applications.The work is focused on the fatigue life evaluation of a joint, which transmits the drive torque from the engine to the oil pump.The aim of the procedure is to calculate the onset of the surface fatigue phenomenon in the hexagonal joint which drives the oil pump, taking into account the axes misalignment and the flat-to-flat clearance.The study has involved several matters, experimental measures, CFD, MBA and FEM analyses. A calculation procedure has been set up in order to consider all the necessary loads applied on the joint.The CFD analysis defines the hydraulic resistance loads on the pump. The FEM analysis is used to define the joint contact behaviour in terms of stress and strain and the surface pressure on the driving surfaces. The MBA defines the dynamical behaviour of the joint and it works out the load time history. The input shaft rotational velocity is imposed. It is obtained via experimental measures of the rotational velocity taken on the fired engine.The presented surface fatigue analysis method is a hybrid methodology which involves several calculation software packages and experimental data. The method is useful to design and verify drive joints subjected to torsional vibration, which typically undergo the pitting phenomenon.In the end, this new design tool in the PPT know how portfolio has led to a better products knowledge and to time-to-market reduction.