Adjustable length crank arm for a bicycle

A crank for a bicycle comprising a crank arm having a through bore at one end thereof and annular recesses in continuation of said through bore on opposite first and second sides of said crank arm, a pedal shaft having a screw threaded portion, a first adapter fitted into said through bore at a pedal shaft mounting side thereof, said first adapter having a first mounting bore which is eccentrically positioned with respect to the center of said through bore and through which said pedal shaft is mounted to said crank arm, said first adapter having at the outer periphery thereof at a side of one axial end of said first mounting bore a first engaging portion larger in diameter than said through bore which is fitted into one of said annular recesses provided at said first side of said crank arm, a second adapter fitted into said through bore on said crank arm at a reverse side to said pedal shaft mounting side, said second adapter having a second mounting bore eccentrically positioned with respect to the center of said through bore and aligned with said first mounting bore, and having at the outer periphery at a side of one axial end of said second mounting bore a second engaging portion larger in diameter than said through bore which is fitted into one of said annular recesses provided at said second side of said crank arm, at least one of said first and second mounting bores at said first and second adapters having a screw threaded portion which is screwable with said screw threaded portion of said pedal shaft, an anti-rotation mechanism comprising a plurality of engaging splines extending axially of said through bore and provided between at least one of said first and second adapters and said crank arm which restrains said adapters from rotating with respect to said crank arm, and a connecting means for connecting and drawing said first and second adapters toward each other.