An engine/pump having a crank shaft (1) with a shaft axis (1A) and a crank axis (2A) oblique to the shaft axis (1A) which intersect with each other at X, piston/cylinder assemblies (6, 12) to rotate about the shaft axis (1A) and having a reciprocal axis between its top dead centre and bottom dead centre, the reciprocal axis midway between TDC and BDC being normal to a line projected from X, piston control means (3) to rotate about said crank axis (2A), connection means for each piston (6) from said piston control means (3), to allow reciprocal movement of the pistons (6) within the cylinders (12) as the assemblies (6, 12) rotate about the shaft axis (1A), cylinder head (5) which holds the cylinders (12) in an array, the head (5) including at least one port per cylinder, and ported means (13) relative to which said cylinder head (5) moves sealably to allow timed to the reciprocal movement of each piston (6) in its cylinder (12) and the rotational position, the opening and closing of each cylinder (12). Each cylinder (12) is indexed at a predetermined rate to the relative rotation of the crankshaft (1) through gearing (10). An alternative embodiment of the invention is also disclosed as shown in the figures.