2006 MTD (TORO) 50inch rider w/22hp Kohler

[DeeCeeinFla]

My mower has about 300 hours on it and has developed a problem with the drive idler assembly ( located in the rear inside of the mower frame ) coming loose from its mount.
The first time it happened, it looked as though the short bolt (5/16") located in the underside of the idler pulleys just loosened. After reinstalling the bolt, it ran fine for about 10-12 hrs.
then it happened again. I reinstalled the bolt with locktite (216-red) and it has backed out again after about 6 hrs. What kind of problem do I have ?? Is it a worn belt problem, or
something with the idler assembly ? I need help !

 

[mechanic mark]

Post model & serial numbers of tractor as well as all numbers from engine. Your idler pulleys need to be removed & inspected for replacement, bearings are checked by holding pulley in one hand & spinning bearing with a finger from opposite hand as well as trying to move bearing up & down, if bearing is rough or dragging while spinning it's bad, also replace bolt & use self locking nut to fit. With 300 hrs. on tractor & never been changed, I'd replace all idlers as well as inspecting all belts for replacement.