Rope length for replacing valve springs.

The last one I did valve seals on, I used compressed air and it worked well. I've used rope in the past and it's fine, but if you have access to air it works well too. Heavy shop air will tend to want to kick the engine over though, but only until said piston is at BDC. ....admittedly, not the best place to be when removing the valve springs, but if you're careful it'll be fine.