The three-rotor model introduced in part I (J. Phys. Chem. 1996, 100, 16419) displays transitions of crankshaft type between stable states that are not connected by saddle points of the potential. The method of site localizing functions is employed for characterizing the crankshaft process. We show that its rate is controlled by the torsional dynamics near the bifurcations of separatrices originating from the potential maximum. From the analysis of the probability flux, the picture of crankshaft transitions as sequential and concerted crossings of the barrier by two torsional angles is recovered, like in the concerted torsional transitions found in the simulations of polymers. The identification of the separatrix bifurcations leads to an analytical estimate of the crankshaft transition rate. Moreover, it is shown how such an estimate can be generalized to multidimensional stochastic problems, so opening the possibility of analyzing similar types of transitions from realistic models of torsional dynamics in polymers.