The rear bearing on my 10 or 12si is a small needle roller bearing and has very little room for lube IMO that is the reason for it's short life span, when there is no side loading on it it was near impossible to notice it so you might pull the Alt. and split the case to visually inspect I'd look for the existence of lube as well as signs of excess heat build up a IR thermometer might also give you some info if you can get a reading of just the area of the bearing.So I drove the truck without the belt. There is no noise. Since I have a new water pump and idler, it must be one of three things. Alternator, AC compressor or the idler on the tensioner. All three turn nice as can be by hand.
The tensioner itself is old, but I had to switch the idler on it because I needed one without grooves. I think it is brand new, but I’m not sure because I have a lot of parts, new and used in a box. (It looks new)
The AC compressor is new 5 years ago, but it has just been sitting in a box during that time.
The Alternator is used. I spun it with a drill just now and it turns nice. (I don’t know if the drill turns as fast as the motor.)
Im really at a loss. I’m thinking of ordering a new alternator.