The pilot executed a wheel-up landing after normal and emergency extension procedures failed to properly lower the airplane's landing gear. The airplane sustained damage to the propeller, lower fuselage skins, and fuselage bulkheads. Postaccident retraction tests revealed that the landing gear extended and retracted abnormally. Examination of the landing gear system revealed a deformed spring on the up lock sequencing actuator. The spring was replaced and subsequent retraction tests were normal. Review of the hydraulic system for the airplane revealed that a failure of the up lock sequencing actuator could result in hydraulic pressure being directed to both sides of the main landing gear actuators causing the landing gear to not fully extend. No other preexisting anomalies were found.