Abstract: A method for and an apparatus for assembly of rotating ring rotary compressors is disclosed. A cylinder, shaft, roller and supports are initially assembled together, fixing means being kept in a slackened position. A preliminary centering operation is then carried out for bringing the axis of the shaft into a diametral plane of the cylinder constituting a predetermined reference plane. This operation is carried out by orientation of the shaft into two angular positions spaced from each other by 180.degree.. The shaft is then oriented relative to the cylinder, the region of maximum eccentricity of the core being brought into the said reference plane. The support and the cylinder (this latter with the interposition of the roller) are then pressed onto the shaft by a thrust exerted in the said predetermined plane.