Belt tensioner malfunction
 

I have an xj but I am installing new belts on my non-jeep (gasp!!) but I would think that the earlier jeeps had the same apparatus. This is the tensioner where it is screwed in to loosen and out to tighten. But mine does not work, I screw it all the way out and all that happens is the bolt comes out, no increase of tension. What can I do about this?
OK, I will come clean, this is on a 88 Nissan Van, this forum is so great, thought I would "fish" for an answer.