In recent years, interests in crankshaft analysis are renewed due to crankshaft difficulties in nuclear standby engine generator sets and elsewhere. Difficulties are caused by either deficiency in analysis procedure or in the nature of the fast-start application, or both. The continuous upgrading of the engine rating is another factor. Several advanced torsional calculation methods were developed in the U.S. to cope with this crankshaft crisis. These new methods were needed as neither the classical Holzer-Forced Vibration method nor the conventional classification rules seem rigid enough to determine the magnitude of the safety margin. These obsolete methods are not capable of pinpointing where the failures would be.Since 1983, PEI Consultants has been working actively in developing advanced torsional computer codes to simulate more closely what is actually happening in a shaft system. Several simulation codes were developed for the torsional and damping behaviors of an operating engine-generator system. This paper describes the mathematical derivation of the new codes and its good check with experimental results.In addition to crankshaft torsional and damper simulation, the potential use of torsional response for engine combustion diagnosis is also revised. This paper, 861226-A, is a revised version of that presented in the September, 1986, Milwaukee meeting.