A power takeoff adapter (30) extends a power shaft (10) such as the crankshaft of an engine. The adapter (30) has a pin portion (34) receivable in a complementary recess in the end (12) of the crankshaft (10). The end portion (42) of the pin portion (34) is threadably engaged in a complementarily threaded portion at the inner end of the recess, such that torque applied in operation tightens engagement between the adapter and the crankshaft which may have complementary tapered surfaces (44,40) between which the torque is directly transmitted. Alternatively, the pin portion may have an annular shoulder engaging the end surface of the crankshaft. The end face (28) of the crankshaft can be flush with the outer surface of the crankcase.