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 (111-115) projecting radially outward from the troughed section of the support ring , each tab (111-115) 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 (111-115); 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 (111-115) projecting radially outward from the troughed section of the support ring , each tab (111-115) 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 (111-115); 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 . <EOS>