A torsional assessment is presented of a single cylinder gasoline engine crankshaft. An analytical mass-elastic model of the rotational system was constructed, and consisted of a flywheel, crankshaft, and pulley. This analytical model was correlated against a modal test. The correlated mass-elastic model was incorporated into a larger analytical model which simulated a running engine, and it was correlated against a running engine torsional test.After correlation was established, the large analytical model was used in a parametric study of the crankshaft's torsional status vs pulley inertia. This parametric study revealed that the crankshaft was torsionally acceptable for any reasonable application.