Variable Speed Pulley Assy Keeps Coming Loose

I have a 2015 T-bilt Bronco 42in mower. The bolt that holds the variable speed pulley in place will not stay tight. Even using loctite and a lock washer on the bolt does not keep it from loosening. Then the shaft gets loose and is ruined. I bought new bearings and bearing housing and the new bearings are loose in the housing just like the old ones. My local mower shop where I bought the parts doesn't know what to tell me about this. I'm hoping someone on this site has seen this and can help.     The pulley is number 78.