A powered well string positioner capable of actuation during the vertical reciprocal movement of a well string will increase or decrease the length of the downhole well string length below the wellhead seal upon detection of a string positioning condition within the tubular by a controller. The vertical reciprocal stroke of the power unit of the well is not changed as the downhole length of the well string is varied, and the well string can be adjusted during operation of the well without the need to disassemble the well string.