With a drastic advance of computing software and hardware, recently, simulation techniques play snore important role in development and design of diesel engines. Especially, Finite Element Method (FEM) is indispensable for design of diesel engine components, as a tool of optimizing each part and selecting the Materials. Meanwhile, it is one of the greatest theme for all engine designers to raise compactability and high-performance of small engines. At the same time, we have to respond to social needs, that is safety, reliability, durability, and comfortability, for reduction of noise and vibration. Moreover, for design of engine components, we always try to reduce a period of development and make more economical components because we have to consider those cost.To meet this severe requirement, it is needed not to apply the simulation techniques just as they are, but to establish the higher and more useful ones. In this paper, we introduce some examples of advanced application of simulation technique using FEM to the diesel engine components, with experimental study, photoelastic test and others. As a typical example, we will introduce an evaluation method for fracture strength of a flywheel with FEM.