This paper presents a simple method of estimating steady-state diesel engine disturbance amplitudes that can be used in rigid-body, low frequency vibration modeling to predict the performance of an engine's isolation suspension and its components. The internal disturbances occurring at each cylinder and crank throw are determined and combined to provide the net disturbances for several common four-stroke diesel engine configurations. The method utilizes a simplified Fourier decomposition of diesel combustion and the predominant inertia disturbances from within the engine. With a few pieces of information from the engine maker, actual disturbance amplitudes and phases can be estimated. Conditions and simplifying assumptions are discussed. The estimated disturbance amplitudes can also be used in torsional vibration modeling of the drivetrain.