Gehl 1870 baler chain trouble

 My uncle has a Gehl 1870 baler that has started acting up. Pardon if I don't use correct terms for the pieces/parts.

The big (12-14” diameter) roller in the bottom of the chamber is chain driven on the left side of the machine with a 60 series chain. The roller turns clockwise when looking at the left side; the drive sprocket is in front of the roll's driven sprocket. The “pull” side of the chain is on the bottom and the slack side is on top; the idler sprocket is also on top...on the slack side. That all makes sense to me, but the pull side of the chain becomes slack and the slack side becomes taut when there is a bale in the chamber. It's acting like the belts are turning the bale faster than the roller is turning the bale. To me it appears that the bottom roller is being driven by the bale instead of the other way around.
It became noticeable when a banging (started yesterday) came from the baler as the drive sprocket was getting chain pushed to it from the roller; this allowed the sprocket to climb a tooth, tighten the tensioner/idler, then when the jumped link made it around the sprocket the idler would slam back down.
I cannot see where there was ever a wooden block or idler on the taut side to take the slack. With little pressure, I can use a screwdriver and hold the pull side (which should be taut but is slack) of the chain up and remove the slack. When I do this, the baler runs fine.
The chain is new (tried that first) and has the correct number of links. The drive sprocket is worn some, but not sharp on top of teeth nor are the teeth curled on top.
This baler has been used by them for a few years and worked fine last year. It seems like the barn gremlins have been busy.
I may resort to redneck ingenuity an put a tensioner/idler on the taut side to, but that's just a work around for a problem that I would like to fix correctly if anyone has ideas/experience that could lend an idea?

 

Thanks and 73, Mark

Gehl 1870 baler chain trouble