Massey Ferguson 725 pulley issue.

[jstjoehere]

I just bought a massey ferguson mower conditioner model 725. Got it home thought well Ill see how it works hooked up and went to the field. After mowing a short amount of time the bottom left pulley for the lower roller comes off. This is the pulley that runs the pitman arm for the sickle bar as well. I put it back on didnt get it very tight. tried it again and it comes off again while mowing. Any ideas whats causing this or how to correct it. Im running this machine with a John deere 4105 that has the electric engage PTO on it. I noticed that it slows down to a certain speed then locks in place. Could this be causing the momentum of the rollers to break the pulley on since it is a thread on pulley?