as spanner90 said on the Iroquois UH1-H we were told not to turn the rotor in reverse as the xmsn driven generator(only one hyd system gen driven from top fwn of xmsn) had angled brushes and you could damage them if turned backwards, but that is the only helo I've heard about with that , the 205 had 2 hyd systems and the main gen was eng driven.