Just to try it I got the Husqvarna out this AM

[ericforster]

If you continue having this issue even with a locking nut, maybe consider tightening the nut and damage the threads so it wont back out. Its not the perfect solution but it will keep the nut on. Another option would be a jam nut.

 

[ericforster]

My jd uses jam nuts on the pulleys for the blower. They hold very well.

 

[JDJake]

Could also install the nut, then drill a hole through the bolt left sticking out and install a roll pin or cotter key.