The rod-free mechanisms are used for converting rotational motion into reciprocating motion and vice versa. The mechanism can be used in displacement pumps and compressors, as well as in internal and external combustion engines, cubic expansion engines, steam engines, hydro and pneumatic engines. Coulisse-eccentric motor automatically feeds and distributes the actuation fluid to the swept-volume capacities. Coulisse-eccentric motor is easy to manufacture, contains a minimum of parts, such as a housing, a coulisse and an eccentric, can be made entirely of ceramics, and allows converting the pressure difference between the two internal volumes of the coulisse into rotational motion on the shaft, and vice versa. Coulisse-eccentric motor in motion allows reversing, changing the shaft torque and compression ratio, while all engine components operate normally and are not subjected to excessive loads.