Locking spacer assemblies, rotor assemblies and turbomachines are provided. In one embodiment, a locking spacer assembly includes a first end piece and a second end piece each configured to fit into a space between platforms of adjacent rotor blades, the first end piece and second end piece each comprising an outer surface and an inner surface, the outer surface having a profile adapted to project into an attachment slot, wherein the inner surfaces of the first and second end pieces generally face each other. The locking spacer assembly further includes an actuator movable between the inner surfaces, the actuator comprising a projection configured to engage the inner surface, the actuator further comprising a plurality of locating protrusions extending from the projection, the locating protrusions configured to fit within locating channels defined in the first end piece and the second end piece.