A system to retain and control the position of a shroud ring relative to rotor blade tips comprising: a rotor configured to rotate about an axis, the rotor having a series of blades each of which projects radially outward from the axis to one of the rotor blade tips; wherein the shroud ring comprises a non-metallic material, has a peripheral groove and surrounds the series of blades with a clearance defined between the blade tips and the shroud ring; a support ring comprising a metallic material configured to axially locate the shroud ring through a troughed section engaging in the peripheral groove from a radially outward direction, and the support ring including a series of tabs projecting radially outward from the troughed section of the support ring, each tab having an axially extending aperture; a retention spring engaging the troughed section of the support ring from the radially outward direction, the retention spring configured to apply a radially inwardly directed force on the support ring in the troughed section and the retention spring including a series of openings, one of which registers with each of the apertures; an alignment ring with a series of alignment blocks each defining an opening, one alignment block aligned with each tab; and an alignment pin extending axially into each of the apertures and openings which are aligned radially and circumferentially, wherein the alignment ring contacts an axially directed wall of a case centering the alignment ring therein, and the alignment pins are configured to locate the support ring and the engaged shroud ring concentrically with the rotor about the axis, and, via the alignment pins and the centered alignment ring, positioning of the shroud ring is retained and controlled to maintain the clearance. a rotor configured to rotate about an axis, the rotor having a series of blades each of which projects radially outward from the axis to one of the rotor blade tips; wherein the shroud ring comprises a non-metallic material, has a peripheral groove and surrounds the series of blades with a clearance defined between the blade tips and the shroud ring; a support ring comprising a metallic material configured to axially locate the shroud ring through a troughed section engaging in the peripheral groove from a radially outward direction, and the support ring including a series of tabs projecting radially outward from the troughed section of the support ring, each tab having an axially extending aperture; a retention spring engaging the troughed section of the support ring from the radially outward direction, the retention spring configured to apply a radially inwardly directed force on the support ring in the troughed section and the retention spring including a series of openings, one of which registers with each of the apertures; an alignment ring with a series of alignment blocks each defining an opening, one alignment block aligned with each tab; and an alignment pin extending axially into each of the apertures and openings which are aligned radially and circumferentially, wherein the alignment ring contacts an axially directed wall of a case centering the alignment ring therein, and the alignment pins are configured to locate the support ring and the engaged shroud ring concentrically with the rotor about the axis, and, via the alignment pins and the centered alignment ring, positioning of the shroud ring is retained and controlled to maintain the clearance.