After arriving overhead his destination the pilot selected the landing gear down, but received an indication that the nosegear had not locked down. When the emergency gear extension procedure failed to achieve a nosegear down and locked indication, the pilot diverted the aircraft to Roma. Following touchdown on the main wheels, the nose was lowered to the runway and the aircraft slid to a stop. The aircraft had undergone some routine maintenance at Brisbane before the flight. During this maintenance the Nose Gear Centering Spring Assembly had been changed. Examination of this assembly after the accident showed that an attach bolt, had been incorrectly installed and had fouled the nose gear door torque tube, causing the nose gear to "hang up". The correct installation of the bolt is critical, and is the subject of special mention in several Piper Service Documents and Australian Airworthiness Advisory Circular No. 143.