A cylinder head (3) for an axial flow rotary valve (1). The head comprises a bore (2) having an axis and adapted to house an axial flow rotary valve (1), a window (8) in the bore through which at least one port (12, 13) in the valve periodically communicates with a combustion chamber (9) as the valve rotates, at least two axially extending slots (21) in the bore, adjacent opposite sides of the window, each of the slots being adapted to locate a floating elongate gas sealing element (20), and at least one spark plug hole (7) adjacent to the bore and adapted for mounting a spark plug associated with the valve. The head further comprises at least one elongate axially extending cooling passage (24, 25 26) disposed between the bore and the spark plug hole, adjacent to one of the slots, the passage having a substantially constant cross section and extending axially at least over the length of the slots.