Hello! I am relatively new to Mooney ownership and brand new to this forum. Last August I bought a 77 M20J and it has been a wonderful airplane so far, minus a couple squawks, this one being the most irritating. In cruise flight (above ~120kts) the airplane likes to roll to the left quite heavily. I flew it with the previous owner twice before buying and it did not do this. The issue seemed to start after the pre-buy and annual that was done last August. In flight with my hands off the yoke and feet flat on the floor the airplane will roll left at a relatively decent rate, slightly uncoordinated. Here is what I have checked so far:
Rudder / Aileron interconnect springs: Both springs are still attached and in good condition. When on the ground and moving the yoke to the right I feel spring pressure and when letting go the yoke will spring back past center to the left. When moving the yoke to the left there is no spring pressure and it will stay in whatever position I leave it in left of center. The yoke is level and centered in flight. Are there any other springs in the aileron control system that could be broken or disconnected? I have looked through both the maintenance manual and parts catalogue and cannot find anything of the sort.
Flap rigging: I figured the right flap, being that it is on the side of the airplane with the door, had maybe been stepped on or damaged at some point and was not retracting fully, thus creating more lift on the right wing while in flight with the flaps up. Using protractors and adjusting the flap up stop bolt I matched the right flap position to the left. The issue remained.
Parasitic drag: With the airplane on jacks and the gear up, all of the doors seat properly and nothing appears out of position. There are no inspection panels or anything hanging down or unattached on the bottom of the left wing that would cause any excess drag on that side of the airplane.
Engine mounts: The engine does appear to sag very slightly. Based on the logbooks the engine mounts have been shimmed once about 4 years ago. During the annual the IA determined that the mounts did not need to be replaced just yet, and it does not appear that the engine is out of position where it could negatively affect in flight characteristics. I am considering preemptively replacing the mounts anyway.
The airplane also has the original Century 2B autopilot (roll only) that works somewhat well. The roll tendency tends to overpower it though. I also am not ruling out that the old servo may be part of the issue.
My next plan of action is to find a shop that specializes in Mooney's (at least has travel boards) locally. I am in the Seattle area and don't know of any shops that can check rigging on Mooney's locally short of LASAR in eastern Oregon. Any insight would be much appreciated! Most of the time I fly the airplane locally and keep the right wing full of gas and that seems to counteract the roll well enough but I have some long cross countries planned for this summer and will need more than one full tank... I attached a photo of the turn coordinator in flight with hands and feet off the controls taken immediately after letting go of the yoke. The left bank will continue to develop within seconds if not corrected. Any ideas or information from the seasoned Mooney owners would be great!
Thanks!