Sheared flywheel key on a 10hp? Hmmmm that's strange.I've only had 1 engine sheer it's flywheel key and that was because the new coil I got was faulty.For some reason it was firing to soon and caused the engine to kick back hard while cranking it.Good thing it was on an older tractor equipped with starter genny or it would of ripped the teeth off of the starter and possibly the ring gear.
I ended up replacing the aftermarket Stens electronic ign. coil for a points coil and put new points and condenser in it.Man it starts so easy now.
This was on my MTD Fourteen Hundred with 14hp cast iron briggs single cylinder.
I refuse to buy any more Stens coils.This is the 2nd one in a row that was bad out of the box.