A rotary machine core assembly (10, 40, 50) comprising: a rotor housing defining a trochoid bore, the rotor housing having a plurality of pairs of fixing holes (24a, 24b, 42a, 42b, 58a, 58b) provided therein, each pair of fixing holes comprising a first fixing hole (24a, 42a, 58a) extending from one side of the rotor housing part-way into the rotor housing and a second fixing hole (24b, 42b, 58b) extending from an opposing side of the rotor housing part-way into the rotor housing, the fixing holes being generally co-axially aligned such that they extend towards each other and each fixing hole having a depth such that the ends of the fixing holes are spaced from each other; a first endplate located adjacent the one side of the rotor housing and a second endplate located adjacent the opposing side of the rotor housing, each endplate having a plurality of through holes (30, 32, 54, 56) provided in it, the through holes being correspondingly located with the fixing holes on the respective side of the rotor housing; a plurality of mechanical fixing elements (18a, 18b), each mechanical fixing element being located through a respective through hole in one of the endplates and being received in the respective fixing hole in the rotor housing such that the ends of oppositely located fixing elements are spaced from each other; and wherein each mechanical fixing element (18a, 18b) extends part-way into the respective fixing hole characterized in that a respective connecting bore is provided through the rotor housing between the ends of the oppositely located fixing holes (42a, 42b) of each pair, said connecting bore has a diameter which is less than a diameter of each of the fixing holes (42a, 42b) of the respective pair. a rotor housing defining a trochoid bore, the rotor housing having a plurality of pairs of fixing holes (24a, 24b, 42a, 42b, 58a, 58b) provided therein, each pair of fixing holes comprising a first fixing hole (24a, 42a, 58a) extending from one side of the rotor housing part-way into the rotor housing and a second fixing hole (24b, 42b, 58b) extending from an opposing side of the rotor housing part-way into the rotor housing, the fixing holes being generally co-axially aligned such that they extend towards each other and each fixing hole having a depth such that the ends of the fixing holes are spaced from each other; a first endplate located adjacent the one side of the rotor housing and a second endplate located adjacent the opposing side of the rotor housing, each endplate having a plurality of through holes (30, 32, 54, 56) provided in it, the through holes being correspondingly located with the fixing holes on the respective side of the rotor housing; a plurality of mechanical fixing elements (18a, 18b), each mechanical fixing element being located through a respective through hole in one of the endplates and being received in the respective fixing hole in the rotor housing such that the ends of oppositely located fixing elements are spaced from each other; and wherein each mechanical fixing element (18a, 18b) extends part-way into the respective fixing hole characterized in that a respective connecting bore is provided through the rotor housing between the ends of the oppositely located fixing holes (42a, 42b) of each pair, said connecting bore has a diameter which is less than a diameter of each of the fixing holes (42a, 42b) of the respective pair.