sdandrea1 You mount the spring on the shaft. Anchor one collar/ end by tightening the clamp bolts. Wind the other end collar (it was 21 strokes when I did it) using rebar posts as levers,, in the collar holes, one in each hand, then tighten the clamp bolts at that end. Just don't let the rebar slip out of those collar holes, especially after you get about 10 winds in. They could become a launched spear that will pierce your skull and kill you very dead.
There is a local company that advertises spring replacement on TV commercials. The tech uses a cordless drill to wind up the spring instead of the winding it up with the bars. Looks much safer. They probably exist but I would think with todays technology there is a door that has no springs and opens and closes with a motor.