a piston assembly is disclosed . in one aspect , the piston assembly includes a rotary piston , wherein the rotary piston comprises a first axis of rotation , a central bore having bore axis and at least two curved first constraint surfaces , and wherein the bore axis substantially corresponds to the first axis of rotation . the piston assembly also includes a substantially hollow - cylindrical bearing ring configured to be at least partially inserted in the central bore . the piston assembly further includes at least one fuse body configured to connect the rotary piston and the bearing ring , and to transmit , at least temporarily , a force in the two opposite axial directions relating to the first axis of rotation between the rotary piston and bearing ring .