Pilot reported a loss of pitch control due to incorrectly installed elevator trim tab servo while conducting a break in flight for a newly installed right engine cylinder. Trim tab servo connecting cables had been reversed which caused excessive pitch and nose up control forces during climb and subsequent return to field for landing.

Narrative

The aircraft had not flown for a couple of months. During its down time; a cylinder on the right engine had been replaced and a break-in flight was dictated. The planes right engine had been replaced and a break-in flight was dictated. The plan was to put at least an hour on the new cylinder using typical break-in procedures. I was the last person to fly the plane. For this flight; a reasonably thorough ground preflight was performed and nothing appeared out of the ordinary. Prior to takeoff; the aileron; rudder and elevator trims were set and rechecked. Shortly after liftoff; elevator down-force got slightly heavy (plane pitching up) and forward trim was applied. As I accelerated; the necessary down forces increased. Initially; I presumed that the acceleration was responsible for the increased necessary down-force and momentarily thought that the electric trim was not functioning. I now utilized the manual trim to trim more nose down; but as the plane accelerated; the down-force continued to increase. Out of 500-600 ft AGL I realized that the forward trim had reached its forward stop. By this time nose was trying to pitch up dramatically. I would estimate that it took 30-40 lbs. of forward yoke pressure to counter the pitch-up forces. Airspeed was about 120 KIAS and I had already reduced power to reduce the airspeed. I contacted tower to advise that I was aborting the mission and requested permission to land. In the downwind; gear-down was selected. Wing flaps were then cautiously selected to APP. After turning final; landing flaps were cautiously and incrementally deployed. The landing was uneventful.Upon taxi return to base; I exited the plane to find that the trim tab was fully deployed upwardly; causing the elevator down force. Unbeknownst to me; during the aircraft's down time; an elevator trim servo had been replaced at which time the connecting cables to the trim tab had been reversed; clearly a maintenance error. The major mistake that I made; was in not reviewing the maintenance log prior to the flight; which was standard procedure for the company and its pilots. I was pre-programmed to believe that this was nothing more than a routine cylinder break-in flight and an exercise flight for the plane. I knew that I had been the last pilot to fly the plane. There had been no previous discrepancies with elevator trim or any control surfaces. What was later revealed to me; was that; due to a previously noted servo part-number discrepancy; the company had decided to change the trim servo to what they knew to be the correct part number. This had been appropriately noted in the company maintenance log; which I had failed to review prior to flight.Disaster averted. Any number of things could have made this outcome less satisfactory. With a more aft CG; I suspect that the plane would have not been controllable. If not in good VFR conditions; the severe pitch-up may have been temporarily been misconstrued as instrument error; leaving little time to determine corrective action. Lack of overall experience and experience in type may have left another pilot too confused to not take the necessary action to maintain control of the plane.