Adjust the lock nuts on the threaded rod. It's not letting the adjuster travel far enough. You probably changed something when you replaced the bearing. I think the adjuster needs to be able to travel closer to the combine.
I think 3020 is on to something here - But heres my 2 cents worth - If I remember right - you had to pull out that little pin to take the belt off and get to the bearing - you can move that arm all the way around -If you did spin it out then 3020 is right - it's to far out - or the belt is wore and sitting down in the pully to much - I think I would pull the pin and spin it in some and try that .
