four stroke engine furthermore it will be seen that the side loading on each piston assembly 32 during the power stroke is in the direction of rotation of the cylinder assembly 20 whereby that rotation is enhanced by the piston side load if desired 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 and 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 banks 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 bank having their axes in a common radial.