I have a 3.5 hp tecumseh motor I was planning on putting in my Rutman frame. It had a pully on it when I bought it which was held on by a bolt in the center of the pully and a set screw. It is a 3/4 inch shaft with no key way in it Is it possiable to put a clutch on this type of crank shaft I didnt know it was a round smooth shaft until I removed the pully any Ideas would be helpfull