Lionel 6-38049 Norfolk and Western 2-6-6-4

I have been given this locomotive to work on for a friend. It runs very jerky on start up and very low speed. I have pulled both motors, and the motors and wheel truck assemblies turn over smoothly by hand. Everything has been properly oiled and greased. I set a stall speed, and then took it back off it did not help. I also noticed that the ring under the flywheel on the rear can motor came loose. I slid the ring back up under the flywheel,so it did not hit the sensor board.  Is there any specific distance between the ring and the motor sensor. And can the ring be glued into place with an adhesive like foam tac or something to keep it from moving again. Any suggestions would be greatly appreciated.