Abstract: This invention concerns balancing reciprocatory machines, such as internal combustion engines, in which reciprocating movement of a piston or the like is translated into rotation of a crankshaft via a connecting rod. In order to provide at least a significant degree of compensation or balancing of forces causing vibration in the machine, the crankpin has a pair of heart formations fixed thereon which makes rolling contact with a pair of rain drop formations rotatable on an extension of the connecting rod. At T.D.C. the point of each of the rain drop formations fits in the cusp of the appropriate heart formation and at B.D.C. the maximum radius of the heart formations coincide with the minimum radius of the rain drop formations.