The bolts are tight and I see no signs of anything moving. With the weighted tires on I can step off the tractor with it against a stump and it'll still slip. The BGB pulley is spinning, the belt is smoking when it slips. The second belt is tight. The second belt often sticks for a bit but it lets go after a few seconds, the result is a momentary creep forward.
In reverse, the second belt lets go, the band tightens up and it goes, the BGB pulley don't slip at all. Nothing else appears to change.
The part that gets me is that the outer belt is so loose, even with a shorter belt, there's almost no tension on it. I can lift it off the pulleys in forward with one finger, there's less than 5 pounds of tension on that belt. When the inner belt is tight, its tight and you can't pull it up off the pulleys. The tensioner simply don't seem to apply any tension, regardless of how much spring pressure on the other end of that linkage. If I remove the inner belt, the outer belt gets tight. If I switch to a shorter belt it still don't feel tight. The only way to get it 'tight' is to rim on a belt so short it fits like a tire on a rim. Even then the BGB pulley will slip. The belt is bottoming in the groove, but only after its slipped a few times. It don't ride that low normally, but its pretty low in the groove.
The inner belt is an original AC part number, what I noticed is that the 1/2" wide AC belt is wider than the 1/2" new belts, all of them. The shape of the belt is different as well. The angle of the sides is steeper and the bottom of the belt is narrower since the belt is thicker. If the belt wasn't so deep or thick, it wouldn't bottom in the pulley. Of course a proper belt will only make the belt ride better, it won't help the lack of tension.
I keep going back to the last parts tractor which has good tension on its belt, but I can't see why or what is different. That tractor is complete in the rear end. It takes a lot of force to retract the tensioner, which I figured was spring pressure but I've swapped over the springs and nothing changed.
I can't imagine that the belt should be this loose, if it were a fan belt on a car it would no doubt be slipping.
Once the weather clears a bit I'll be swapping over the whole linkage set from the other machine, if that don't work, in goes the three speed, but even then I have my doubts as to whether or not it'll slip the same way.