A rotary valve internal combustion engine has a piston (1) connected to a crankshaft (3) and reciprocatable in a cylinder (2), a combustion chamber 4 being defined in part by the piston. The engine has a rotary valve (5) rotatable with a close sliding fit in a valve housing (8) fixed relative to the cylinder (2), the rotary valve having a valve body containing a volume (9) defining, in part, the combustion chamber 4 and further having in a wall part (11) thereof a port (1)2 giving, during rotation of the valve, fluid communication successively to and from the combustion chamber via inlet and exhaust ports (13), (14) in the valve housing. The rotary valve and the valve housing are both formed of aluminum.