The comparison of computed and measured vibratory properties for structures of this complexity is a severe test on the FEM. In order to predict the forced response a knowledge of the acting internal forces is required. These forces may be specified by measurement or analysis, though usually it is not feasible to obtain a detailed description of them. For the CSRs, calculations are based on the concept of a unit magnitude flat in-cylinder pressure spectrum. The use of this excitation results in forced vibration data in the form of transfer functions which are readily comparable with experimentally derived results. Pressure forces are applied directly to model cylinder flame faces. Forces on the main bearings are calculated by means of calculated transfer paths through the piston / connecting rod / crankshaft assembly. Mode shapes, resonant frequencies and forced response of the CSRs for frequencies up to 2500Hz were computed via the model illustrated in figure 5. The resonant frequencies were generally predicted to within 5%. Mode shape prediction and forced vibration analyses yielded results which compared well with those measured on CSRs. Further details on this work are given in reference Tyrrell and Croker (1987).