Street Demon tuning experience

What is this "spring tool" you used, care to share a pic?

Don't worry about damaging the piston, by the time you put enough force on the piston to cause a dimple (which isn't a big deal to begin with) you'd likely bend or break the stop tool itself. And you'd have to crank it pretty hard after you felt the resistance on your breaker bar of the piston hitting the stop tool.