Small Engine Troubleshooting Problems? Ask a Mechanic Now.
If the input shaft is spinning freely, the only way to be sure is to take the case apart, which means pretty much disassembling the tiller since the frame rails have to come apart to get to the case. I've attached a drawing showing you what's inside. Hopefully you just have a broken chain, since most of the parts for this unit are not available any longer. Hope this helps. Let me know...
Chain Case Parts List