Compressor having capacity modulation

A compressor comprising:

• a shell assembly having an end cap at least partially defining a discharge chamber and a pressure chamber;
• a first scroll disposed within the shell assembly and including a first end plate and a first spiral wrap extending from the first end plate;
• an second scroll disposed within the shell assembly and including a second end plate and a second spiral wrap extending from the second end plate, the first and second spiral wraps meshing with each other;
• a piston including a main body and a flange portion extending radially outward from the main body, wherein the main body threadably engages the first scroll, wherein the flange portion is received within a recess defined by the end cap such that the piston cooperates with the end cap to define the pressure chamber, wherein the pressure chamber is in selective fluid communication with a source of working fluid to control movement of the piston relative to the shell assembly;
• and
• a piston-retention member pivotably mounted to the piston and selectively engaging a rotationally fixed structure, wherein the piston-retention member allows threadable rotation of the piston relative to the first scroll in a first rotational direction to threadably tighten the piston to the first scroll, and wherein the piston-retention member selectively engages a selected one of a plurality of notches formed on the rotationally fixed structure to restrict rotation of the piston relative to the first scroll in a second rotational direction to restrict the piston from threadably loosening from the first scroll.