> Do I just need a couple rods of the appropriate size to wind a little
> more tension into the spring? Presumably I should put a rod in, hold
> it, and loosen what looks like a set screw, then wind a turn into it,
> reset the set screw, test, etc.?
I've never done. I've watched it being done by a pro.
He had two rods that fit the holes very snugly. He did one side
at a time: draw a line across the spring horizontally. Put a rod
in the top hole, pull down 1/4 turn, put rod in the now-top hole
which holds the assembly in place, repeat.
Then do the other side, use the line you drew to match up the turns
from side to side rather than trying to count.
> Be careful. Lots of force involved.
What he said. Be very careful and deliberate. Wear safety
goggles. If something slips and lets go, don't try to catch it!
The line you drew will let you get back to your starting point.
Snug fit on the rods seemed to be critical. He had 3/8" steel about
2' long that had been turned to the correct diameter at the ends.
Be careful. Lots of force involved.