Abstract: The inventions include a two- or four-cycle internal combustion engine constructed with a simple inventive coupling, and coupling drive mechanism, which provides for a combined engine, coupling and coupling drive mechanisms in an inventive form of a hand-held power source. In a broader form, the inventions include the portable power source and a system of couplingably attachable manually-controlled, e.g., hand-held, drive assemblies and toolheads, which when coupled to the power source is driven at the attachments first means for receiving mechanical energy from the crankshaft. Functional attachment may include structure into which the power sources are inserted or mounted to drive. The functional attachments are hand-held power tools but for the power source, and include reciprocal coupling mechanism for mating with power source coupling mechanisms.