Alignment of machine components within casings

A machine component of generally circular cross-section, such as the combustor of a heavy-duty gas turbine engine, must be accurately positioned within a surrounding 5 external casing that comprises bottom and top halves of the casing bolted together at a split line occupying a horizontal plane. To enable this, the component and the bottom half of the casing are provided with complementary interdigitating members at three circumferentially spaced-apart locations, comprising first and second locations at the split line on respective first and second horizontally opposed sides of the component, 10 and a third location at bottom dead centre. After lowering the component into the bottom half of the casing to engage the interdigitating members at the three locations, jacking apparatus is operated independently at each location to incrementally reposition the component within the bottom half of the casing. Shims are then inserted between the interdigitating members at the three locations to maintain the 15 jacked position of the component. The jacking and shimming steps are repeated as often as necessary to attain a desired position of the component within the bottom half of the casing. Special fixtures at each of the three locations facilitate the jacking operations. 20 Fig.2 t i t 4Ni00 00*