The snowblower manufacturer didn't put in any shear pins, instead a break away pully hub. When you overload the blower in 10" of deep slushy snow "mashed potato's", the pully can fly off the shaft! The fix will take a few minutes with a hand file and then a vise to press it back on. This time bigger than stock spot welds in all the corners.
STATUS UPDATE 1/21/2011
I found that the hex was a bit loose, and no press fit needed once the bent metal was filed off. It would appear that there was a head on the pulley that was swaged over the face of the pulley to hold on the hex. I put 6 spot welds on the corners of the hex and put it back in. Working good. If if breaks again, I'm going to look into a quick disconnect hub and pulley and use bolts with notches in them to function as shear pins. It's a real bugger to get the hub off to do a proper weld on the bench, I had to pull the shaft out to drive the it thru the hub using the vice. If your lucky the hub will pull off easily, if you can get a puller on it (uggh), 3" holesaw would be handy. McMaster Carr has replacement pulley's relatively cheap, it's likely worth having one on the shelf for a backup. Also, I recommend changing the pulley effective diameter in place of changing the sprocket size. The clearance on the chain housing is a nightmare to open up, and the pulley has no clearance issues. It may be possible to keep the stock belt length with a new smaller pulley if the tensioner has enough travel? Live and learn. Still like the overdrive regardless, now looking for more power, maybe a B7100!