Clutch Problem

While mowing yesterday the clutch on my Ferris IS 1500 broke off from the mower. I did find the bolt and noticed that is was sheared off. My question is what would cause this to happen and is there more to this repair than just replacing the clutch. Any input greatly appreciated.

Broken bolt will have to be removed from crankshaft. Sometimes you can get lucky if bolt is protruding from crankshaft. If you want to give it a try be sure to wear safety glasses and gloves. For safety, remove negative cable from battery, park brake on and key out of ignition. With a small center punch and ball peen hammer, try turning broken bolt counterclockwise out of crankshaft. Do not hit crankshaft when tapping punch with hammer. If you get broken bolt out, keep it temporarily, it's either a grade 5 or grade 8 bolt. You will need broken bolt when matching thread size, bolt diameter, and bolt length. New bolt will need to be torqued to specifications. Check Ferris website for specifications.
http://www.ferrisindustries.com/us/en/operator-manuals/

First thing I'd do is, spray some lub on the broken bolt in the crankshaft to keep it from forming rust. Because there is no pressure on the bolt, it should turn out quite easily, unless you let it rust. If you didn't stike something with a blade, I would think, a faulty bolt from the getgo. When engaging the clutch, you should return the engine to near idle rpms. There is an instant jolt on the clutch and the bolt securing it, every time it is engaged. The higher the rpms, the higher the jolt or stress. The clutch is built to obsorb some of the jolt but, not at high rpms. Look at the broken bolt carefully to see if it had been partially broken for some time. gregjo1948