Last winter we did a little adjusting and attempted to square up the fan clutch on a 1995 N14 in my IH 9400. For some unknown reason, it was slightly crooked. I talked to a couple guys that said to shim it with a washer, but to align it we had to shave a little off one of the mounting pads on the fan clutch to keep it from sticking too far out. The old belts were worn out, so got new ones. The pulleys look like new, and the new belts didn't sit fully flush in the pulleys. New belts were the same number as the old, so we figured it would be fine. Well, driver had mentioned it was squawking a bit when the fan kicked in, so this morning I tightened the belts a bit. He ran for a few hours, and then when I was leaving the pit I noticed a belt on the ground. Opened the hood, and the remaining belt was flipped over, when he shut it off it spun itself off. I called International to verify belt numbers, they were correct. The belts are close to $100 apiece, and we didn't want to waste another $200 on belts, so we put a couple of Gates B44s on instead. They sit about 3/16" deep into the pulleys, but aren't bottomed out so we're going to run it and see what happens. The belts we were using cross exactly to a Gates TR28463. The Fleetgard number is a FLTBT28467, and the Navistar number is a 489001C92. Not sure what we have going on, there doesn't appear to be a belt made that fits these pulleys exactly.
Pulleys are shot. Fan clutch mounting bracket is off, not bolted straight on water pump housing and or Accessory drive depth is wrong, late BC's and early N14's had some issues with depth of accessory drive pulleys not lining up. But without proper attention it will cause the engine to burn up in two years.
We never could keep belts on one of my 60 series (I think the pulleys were worn as truck shop mentioned). We put on new pulleys and got a gates "tandem" belt where the two belts are joined together. I fussed around forever trying to get it to quit throwing belts, trying to align it even after the new pulleys, and the dual belts I think are what finally stopped it.
By what metric are the pulleys shot? They look perfect, not a groove or ridge at all. The new belts do not sit down flush in the grooves, they sit up between a 1/16" and 3/32". There doesn't seem to be a belt made that measures about 11/16 wide, and that seems to be what it needs.
I only bought Cat belts.