Abstract: A crank arm for a bicycle includes a crank arm body having a pedal attachment hole on a first end thereof and a spindle attachment hole on a second end thereof. The crank arm body defines an elongated interior cavity surrounded by a shell, wherein the interior cavity is open to an exterior of the crank arm body. The opening can be used to access the cavity during and after manufacturing. The shape of the cavity may be varied to produce a lightweight yet strong structure. In the method used to form the crank arm body, a mold core formed by a shell containing a sand-like filler material is positioned into a casting mold so that a melt space is formed around the mold core, molten metal is poured into the casting mold, and the molten metal is solidified to form a crank billet. The filler material may be removed through an opening in the crank billet.

Abstract: A crank arm for a bicycle includes a crank arm body having a pedal attachment hole on a first end thereof and a spindle attachment hole on a second end thereof. The crank arm body defines an elongated interior cavity surrounded by a shell, wherein the interior cavity is open to an exterior of the crank arm body. The opening can be used to access the cavity during and after manufacturing. The shape of the cavity may be varied to produce a lightweight yet strong structure. In the method used to form the crank arm body, a mold core formed by a shell containing a sand-like filler material is positioned into a casting mold so that a melt space is formed around the mold core, molten metal is poured into the casting mold, and the molten metal is solidified to form a crank billet. The filler material may be removed through an opening in the crank billet.

Abstract: A crank spindle unit includes a crank spindle having an outer peripheral surface defining a first end, a second end and a hollow central portion. A plurality of first serrations are formed on the first end of the crank spindle, and a plurality of second serrations are formed on the second end of the crank spindle. A first guide surface having a first guide surface diameter is formed on the outer peripheral surface continuously with and inwardly from the plurality of first serrations, and a second guide surface having a second guide surface diameter is formed on the outer peripheral surface continuously with and inwardly from the plurality of second serrations. A first track groove is formed on the outer peripheral surface in proximity to the first end of the crank spindle, wherein a lowermost surface of the first track groove has a first track groove diameter.