The current document presents the development of a structural fatigue assessment for motorcycle engine housings. This methodology is made with a dynamic approach using the modal superposition approach. The project was developed inside the company KTM Forschungs & Entwicklungs GmbH to improve the accuracy of the current methods. Initially the need to implement a methodology with the dynamic approach will be presented. Because this need is specific to motorcycles, a brief introduction to petrol combustion engines will be made with focus on the motorcycle engine characteristics. The method will involve a series of Finite Element Method simulations, the validation of the virtual model properties with a test and the complete fatigue assessment. Engineering basic knowledge is needed to completely understand the numerical methods and the hypothesis made, so basic theorical support will be presented. This includes: an introductory chapter on dynamic mechanics with focus on the forced excitation case, a brief presentation of the Finite Element Method (for both static and dynamic approaches) and basic metal fatigue strength assessment theory with the particular computation method of the specific software used. The methodology will be presented throughout the different phases of the project: modelling and load generation, validation of the numerical properties and modal superposition with the safety result discussion. Especial effort will be made to present all the model generation hypothesis as well as the load case combination. A detailed discussion of the results will follow that will be divided into 2 blocks: the assembly (static part) and the operation parts of the simulation (dynamic part). The technical viability of the method will be presented in the fatigue assessment, with 2 approaches proposed and the comparison with the original full static method. Finally, an economic viability analysis with the estimated social impact of the project is included. Because the method development will be not finished after this project, the main steps to carry out subsequently will be also provi