The old motor shaft is smooth at the tip for like 1/4 inch down then few threads then smooth again. The OS is threaded all the way so how is this going to work casue the old bell was held on by a c clip on the end? And to me looks like the shaft on the old motor is a hair longer than the 18. I was actually thinking of takeing the crank out of the 15 and putting it over in the 18 will this work?