RV-4 pilot reported that an A&P Mechanic incorrectly cleared the aircraft for flight; as the aircraft had significant engine performance issues due to improper work done on the engine timing. At a later time in a different flight; the plane had an abnormal oil pressure and the pilot made a precautionary landing. Upon learning of the latter incident; the A&P Mechanic changed a previous statement regarding the airworthiness of the aircraft. The reporter then learned that the A&P Mechanic was unreliable; and had a history of changing and falsifying records after performing improper mechanical work on aircraft.

Narrative

This is related to pilot's action based on the airworthiness statement from A&P after an annual condition inspection on an experimental aircraft. At the completion of the condition inspection; the A&P instructed me that the plane was cleared for flight. After the initial flight; there were significant engine performance issues from the A&P changing the engine timing. After correcting the timing; the plane was again cleared for flight. This was in the spring time. The A&P retained the log books. On Day 0; the plane experienced an abnormal oil pressure condition and made a precautionary landing. Many weeks later and after the A&P heard that the plane went down;" the A&P filed a complaint that the aircraft was not in a safe condition and not released to fly. The phrase that the plane "went down" was used as the explanation related to why he took the action that he took. His belief appeared to indicate that he thought it crashed; not that it was a precautionary landing.In another case with the same A&P; speaking with Person B; the manager of the Company; stated that she has had a similar problem with the same A&P; Person A; that he was not right in his head; dishonest; incompetent; and would never work on one of their aircraft again. In her case; the company plane had an abnormal oil condition. The same A&P; Person A; worked on the plane and replaced the magneto; which has no relation to oil pressure. Replacement of the magneto obviously had no impact on the condition and she hired another A&P. The second A&P; who was also an IA; found a defective piston and the engine was near catastrophic failure. When Person A; the A&P; learned of the defective piston; he attempted to change; falsify; his logbook entries about his workmanship and airworthiness of the company plane.Given the two incidences of falsification and attempted falsification of records; there are serious risks being introduced to pilots. There are multiple concerns related to this A&P. Pilots are dependent on technical astuteness of the A&P; he is lacking. Pilots and passengers lives are dependent on the assessments and actions of the A&P. Personal integrity and honesty of the A&P are an integral part of aviation safety. There was an exceptional lack of knowledge and skill demonstrated by the A&P on these two planes. In filing this report; it was unclear if this should have been filed as a flight issue or a maintenance issue as there are implications of both."