There are free repair manuals at (old gravelys dot net) - courtesy of Gravely expert Chip Old and many other people. You can view and/or print old the repair manual portions that pertain to starter clutch assembly removal. I've known some guys that have been successful in removing the starter gear w/o placing a blocking device in the cylinder, but many will put either a block of wood or a length of rope inside the head cavity, in accordance with the manual's directions.