A portable tool is disclosed in published German patent application DE-OS No. 32 22 457 wherein a plastic crankcase containing the crankshaft bearings and their respective bearing shells is secured to the cylinder by means of threaded fasteners which pass through the crankcase from below. With this configuration, a substantial portion of the reaction forces occurring in the region of the crankshaft are directed to the crankcase during the operation of the motor and must be taken up by the crankcase. Accordingly, it is necessary that the crankcase be stable and be appropriately constructed since the operational reliability of the tool would otherwise be affected.