Abstract: A drive system comprising a prime mover such as an engine providing a drive shaft, a shell supported by the shaft for rotation relative to the shaft, a split groove pulley mounted on the shaft, the pulley including one flange secured to the shaft for rotation therewith and a complementary flange connected to the shell for rotation therewith, the flanges defining a space axially therebetween, an adjustably movable take-up pulley having a belt-tightening position and a belt-loosening position, and a belt trained about the pulleys. When the belt is tightened by the take-up pulley, the shell and complementary flange rotate with the shaft and the said one flange, i.e., the belt provides a driving connection between the two flanges. When the belt is loosened, the driving connection is broken such that the one flange and shaft rotate relative to the complementary flange and the shell.