Abstract: Theft of a bicycle is discouraged by a locking mechanism in the front headstem that controllably engages the handlebar-attached headstem with the front fork or disengages the headstem and fork for free relative rotation. A shaft attached to the fork and a sleeve attached to the handlebar clamp are connected at a locking junction which is rotatable as a whole in the front journal of the frame. A key operated cam moves a locking roller radially outwardly of the shaft to engage a receptacle in the sleeve for engagement or allows the roller to retract into an aperture for disengagement. The shaft and sleeve have complementary conical tapers axially positioned by a split conical bushing. A cylinder lock operates the cam via a key having a substantially tubular configuration with a uniquely configured axial end for positioning lock pins against axial spring pressure.