A method and apparatus for maintaining a seal between a cylinder and a fluid manifold for a reciprocating force delivery device is disclosed. A cylinder retention assembly comprises a rotatable member with a variable topography surface. The rotatable member is disposed against a stop extending outwardly from the cylinder, and is fastened to the fluid manifold by a locking ring. When rotated, the rotatable member produces an axial force on the locking ring and the cylinder, urging the cylinder against the fluid manifold. The cylinder retention assembly may be used in reciprocating pumps and compressors.