Disclosed herein are methods and devices for repairing articular surfaces in a knee joint. To secure the alternator to a particular engine the alternator is configured by attaching particular mounting ears to particular locations on the periphery of the housing end frames by means of fasteners. The impact tool is mounted upon the boom such that it may be rotated about an axis that is substantially perpendicular to that of the boom. The heat-accumulating passage is provided with a heat-accumulating container, and constitutes a heat-accumulating circuit for causing coolant in the heat-accumulating container to circulate via the engine.