Thank you for your question and I understand your concern.
I am sorry you are having a problem with the chipper. The engine shaft is tapered (no puller available for this) you have to break the impeller loose from the shaft. Remove the bolt and washer holding the impeller on the motor shaft. Start the bolt back in the hole. Run it in until the head is only 1/8 inch away from the impeller. Place a large screw driver or pry bar between the impeller and the rear of the chipper, and pry hard on one side. Hit the head of the bolt firmly with a good sized hammer. The shock will break the impeller loose and it will come off. If the impeller does not loosen up with a couple of whacks with the hammer use a quality penetrating oil and allow it to sit for at least half an hour. If the impeller does not loosen after that, do not continue banging on it, you could damage the shaft or the engine.
I highly recommend calling a service professional to diagnose and repair your chipper. If you get to the point where you need to have a service technician remove the impeller, you can take the chipper shreader into your nearest Sears Repair Center or Sears Store. Here is a link for the Sears Service website that has information on the nearest repair facilities in your area:
Sears Home Services
I hope this is helpful. If I may be of further assistance as more details become available, please reply to this post.