Invention relates to apiston pin assembly for an internal combustion piston engine, which piston pin assembly comprises a piston pin having at its first end (14.1) and its second end (14.2) a first and a second affixing area and between the first and the second ends, at a center area (14.3),, and in which piston pin the first and the second ends having a common first central axis and the center area having a second central axis which axes are offset at a distance from each other. The assembly comprises a power transmission system (102) comprising a circular gear rim (104) arranged to transmit power to the third area of the piston pin, the gear rim being capable engage a connecting rod and the pistonpin to transmit work from rotational movement of the connecting rod in respect to a piston while installed to an engine and the engine is cranked or operated; a locking system (200) which selectively locks or unlocks the rotational movement of at least the third area (14.3) of the piston pin in respect to the piston.