Here is an exploded view of the drive on you MoCo.
Official Case IH Online Parts Store and Case IH Catalog for Best Parts Search and Best Parts Look Up. Case IH Parts for Case IH Tractors, Case IH Combines, Case IH Tractors, Case IH Manuals, Case IH Parts Part #6 is what I believe you are looking for. Through Case/IH dealer here, they are $25 ea.
Shoup shows a replacement sprocket matching that part number, made in USA stamped on it for $16.95.
C5642 - Sprocket Idler - Shoup Manufacturing Company I've purchased parts from Shoup to rebuild the apron chain in one of my old manure spreaders,and they seemed to be quality parts.
Several years ago, I had problems with the drive chain on my old IH 990 MoCo jumping off, mainly when disengaging the PTO. The main drive/driven sprockets were worn so bad, the chain would jump the sprockets, from the momentum of the rollers winding down. The tensioner is designed to keep the chain taught when being driven, so when disengaged, it would lift the tension arm, allowing the chain to slacken, and jump the drive sprockets.
Check the main drive/driven sprockets, to see if they have sharp points. If this is the case, they need replaced. I did a quick check through Case/IH, and it shows those drive sprockets not available, but that doesn't mean they can't be found. I copied & pasted that part number to Google search, and came up with several NOS one's. On my old 990, I had to resort to used parts, out of a salvage yard. Surprisingly, the sprockets looked to be near new, yet at a reasonable price.
Whenever you need a part for your MoCo, or anything else for that matter, use the OEM part number, to get the correct part. Most major manufacturer's have online parts books, to retrieve those part numbers. If said part is shown to be not available, copy and paste the part number to a good search engine, and have a look. I have the best results, using Google.
