Abstract: An apparatus for honing large, long, horizontally-oriented cylinders employs an elongate support beam, extending axially through the cylinder, to support a non-rotating honing head for axial movement within the cylinder. The honing head includes three honing stone assemblies, each stone assembly including a pair of honing stones and an air motor supportably mounted to the honing head by a trailing arm arrangement. Each honing stone assembly is individually biased toward the cylinder wall by an air cylinder, the biasing force variable according to the relative position of the respective stone assembly on the honing head to compensate for gravitational force upon the respective assemblies. Each stone assembly also includes an adjustable stop to selectively limit movement of the honing stones toward the cylinder wall. In operation the cylinder is rotated about its longitudinal axis while the honing head, with a plurality of rotating honing stones, is moved axially within the cylinder.