The pilot reported that he was practicing pattern work and landings. After completing one landing, he back taxied, departed and entered the traffic pattern. While in the traffic pattern he lowered the landing gear; however, it did not extend properly. Multiple attempts to recycle the landing gear and manually extend the gear using the emergency extension procedure were not successful. He elected to return to a tower-controlled airport. The tower controller subsequently confirmed that the landing gear was only extended on the right side. The pilot executed an emergency landing which resulted in substantial damage to the left wing. Postaccident examination of the airplane revealed that the emergency gear extension handle was in the up and stowed position, and the emergency gear extension system worked as designed. The landing gear hydraulic power supply contained a reversible electric-motor driven hydraulic pump that was found inoperable. The electric motor was disassembled, and the brushes were found to be worn beyond limits. In addition, hydraulic fluid and dust were present on the permanent magnets, stator, and windings.