I am not sure how it is driven put what Kerry is saying is a very strong possibility, and what he is discribing are called a woodruff key. Usually one is used to drive a pulley, gear or sprocket. They are used on many engines and other machine devises. I dought that the pulley would be drive by the bolt alone. Take the pulley off and look at the shaft and see if there is a half round slot "keyway" that is machined into the shaft. The key would take all the torque that is applied to the pulley. The bolt just holds the pulley on the shaft. If the bolt has the threads damaged there may be enough threads in the crank to hold a new bolt with good threads. It would not have to be very tight to hold the pulley on with the key doing the drive.
Good luck.