Place sliced bananas in a medium bowl and cover with pineapple juice. Toss gently until slices are coated. Let soak for 30 minutes, then drain. Place bananas in pie shell.
In a small bowl mix sugar and cinnamon. Sift over top of bananas. Dot with slices of butter or margarine. Put on top crust and seal, slashing 2 to 3 vents near center. Bake in preheated oven until crust is golden brown, about 30 minutes. Pie can be served hot or cold.