1 the amount of oil drawn in and therefore the rotor movement can be regulated by restricting the oil inlet port 45 rotor 14 is next pushed up with accompanying expelling of oil from chamber 43 by the compression pressure until spill port 44 is blanked off as the oil inlet port 45 is located near the rotor axis and the spill port is on the peripheral wall 22 centrifuge action of the arrangement together with the pumping action of the rotor 14 causes the oil to be constantly circulated it is thus evident that the rotor floats in cavity 13 as dictated by the pressures and vacuums present in the cylinder and the oil pad in chamber 43 accordingly the combustion forces are taken by the oil pad which overcomes the problem associated with known types of rotary valve engines this results in the engine being of simple design and having a lack of stressed reciprocating parts so that assembly and servicing of the engine is easy with the associated advantage of the engine being very reliable as the rotor is floating between the oil on one side and the various cylinder vacuums and pressures regardless of how low or high on the other side there is never any pressure difference.