Abstract: An apparatus for honing the cylinder walls of a piston engine comprising:A tank having an open top, a vertical column mounted on one side of the tank and being movable along the side of the tank, a generally horizontal lower arm pivotably mounted at one of its ends to the column and projecting over the tank, the lower arm being vertically pivotable in a plane that is substantially perpendicular to the path of movement of the column, a motor pivotably mounted on the lower arm to be vertically pivotable in a plane that is substantially perpendicular to the path of movement of the column, the motor having a drive train terminating in a chuck for receiving the arbor of a rotatable honing stone assembly,An upper arm pivotably mounted to the vertical column and being vertically pivotable in the same plane as the lower arm, a downward projecting cradle fixed to the upper arm and supporting the lower arm, the lower arm being in free sliding contact with the cradle,A spring connecting the rearward end of the upper arm