Incident
The pilot reported hearing a grinding noise when attempting to lower the landing gear. The gear would not extend using either the normal or emergency extension systems. The aircraft subsequently landed with the landing gear in a partially extended position.
Examination
Following the incident, the nose landing gear actuator was examined by the manufacturer. The gear box for the nose gear actuator was disassembled and found to be still packed with grease. While removing the mass of grease from around the drive pinion gear, a small nut was discovered buried and invisible in the grease packed around the beveled gears. The nut was determined to be foreign to the inside of the gear box.
Findings
Examination of the nut revealed indentations on two opposite sides. Placement of the nut on either side of the point where both beveled gears met would jam the rotation in either the retract or extend cycle.
Resolution
On December 23, 1977, the gear actuators were replaced with rebuilt parts.