I'm thinking that the motor was replaced by the previous owner, and it was not the correct motor for this pump... The pump model (sp4020ns) is clearly indicated on a metallic label on the pump housing... And I confirmed that the pump matches dimensions and appearance of the Northstar series in the online manuals. The motor was missinfg one label, but the other label clearly said "Super Pump" and the model# on the motor was Sp2600zlc... When I pulled it apart, the impeller was sp4007. Perhaps when the motor was replaced they also changed the impeller to match the new, wrong motor? Regardless, I am sure the pump is a Northstar, and I need to replace the motor. If that means I need a different impeller, so be it. Will this one work? http://www.ebay.com/itm/320960415104. (piping is 2" or 2.25", voltage is 115, so it appears that the only motor that matches the Northstar specs and my setup is the 2hp uprated motor)