I am rebuilding an Oliver 22A sickle mower. The mower belonged to my father-in-law and we bought it on his sale. I purchased another sickle mower for parts and found out it was an 82 not a 22. I thought about just making a Frankenstein with the good parts from the two but changed my mind and will restore it as close to original as I can. Now my problem, I need to remove the bottom shaft with the counter weight that drives the sickle. On the 82, the sprocket is held in place by a nut. On the 22 the shaft is threaded into the sprocket. I tried holding the input (PTO) shaft and rotating/jerking the counter weight (counter clockwise) but that didn’t work. I ran out of time and thought I would ask if anyone has had one of these apart before. 
Thanks for any suggestions. 
John Schoenauer