A round internal combustion engine (10) comprising: a stationary toroidal combustion chamber (44); a first (24A) and a second (24B) shaft member, each for connecting thereof to at least one piston (26A1, 26A2, 26B1, 26B2) disposed within the stationary toroidal combustion chamber (44); and a positioning mechanism (60), for changing angular positioning and velocity between the first (24A) and second (24B) shaft members, for increasing and decreasing a distance between the pistons (26A1, 26A2, 26B1, 26B2) of the shaft members (24A, 24B), the positioning mechanism (60) comprising: at least one rotatable wheel (28i, 28ii, 28iii) disposed eccentrically (58) within the first shaft member (24A); and at least one rotatable connecting-rod (56i, 56ii, 56iii) disposed between the first (24A) and second (24B) shaft members, for directly connecting an eccentric anchor (36A) of the at least one rotatable wheel (28i, 28ii) to an eccentric anchor (36B) of the second shaft member (24B).