the inlets 40 can be air inlets only and the spark plugs 42 can be associated with fuel injection means for direct injection of the fuel into the air compressed within the combustion chamber of each piston and cylinder assembly the engine is suitably oil cooled with oil passages 45 formed about the outer portions of the cylinder assembly 20 in addition coolant passages 46 may be provided around the closure means 23 the coolant passage 46 may also be oil cooled or it may use a different coolant if desired it will also be seen that the position and size of the inlet and outlet ports 40 41 may be arranged to suit the particular application end of course if desired they can be arranged to overlap one another furthermore the communication between the inlet and outlet ports with the cylinder can be varied independent of each other and of course bands of each of the three cylinder motors may be arranged along a common crank shaft or interconnected crank shafts as illustrated in fig6 and 8 referring to the latter embodiments of the invention it will be seen that the engines have two banks of cylinders 50 and 51 arranged with the cylinders of each band having their axes in a common radial plane centered on a respective crankpin 52 53 the section of fig8 is diagrammatic as it illustrates alternate cylinder closure arrangements at the top and bottom of the section the part spherical surface or surfaces of the cylinder closure assembly 56 may be either a common part spherical surface concentric with the centre of the engine.