An expandable pulley. The expandable pulley comprises a plurality of belt blocks arranged about an axis of rotation. Each belt block bears upon a radial surface extending normally to the axis of rotation. Another surface of each belt block bears upon a conical member surface which is moveable coaxially with the axis of rotation. A spring bears upon the conical member which urges the conical member in an axial direction, which in turn urges the belt blocks radially outward to compensate for a belt length change and to maintain a belt tension. An elastic member holds the belt blocks in contact with the conical member.