The way I set up K/KH springs is: 1. Coil bind your spring in the vise(don't smash it, but lightly coil bind) and measure the length with digital caliper(write it down
A). You may add +.050 to this figure to be safe. 2. Slip a valve in the guide, add the top collar and keepers(no spring) and pull it up tight and level. Now measure with your digital caliper the distance from where the spring will sit on the guide and where it sits on the step under the top collar(write it down
B.). 3.
Now subtract your cam lift from your #B figure.(write it down
C). 4.
Now subtract A from C - What's left will be the actual length you want to make your lower spacer. 4. Next, I buy the
V-Twin 11-0812 lower spacers. They have a nice lip for the lower part of the spring to fit in and it centers it on the guide. You can turn these spacers in a lathe for more travel, or add shims/spacers underneath to take up the extra space. Basically, you want your spring to be about .050 from coil binding when your cam is at full lift. Even .075-.100 is probably ok if you want to be real safe.
I think Leineweber or Sifton uses .020? Then you get the most seat pressure(Installed spring pressure) and the strongest spring tension to pull that valve shut at high RPMs - and it keeps your roller on the cam lobe. Any springs I've used over 100lbs, 110lbs, 120lbs of pressure (tested in my spring tester) I have never floated any valves. You don't need 150lb valve springs with KHK cams. That's just robbing power. You can feel the drag from heavy valve springs when you manually turn over an engine on the bench. You don't need any stronger springs than necessary to do the job. If you ever have some springs that are a bit shorter, or weaker, and that's all you got - put them on the Intake Valves, 'cause if they float a bit, you'll never notice. Put your best springs on the exhaust valves when in doubt. This is good advice - Print and Save.
Note: After I make my spacer, I slip the valve back in the guide, drop my spacer(and shims if necessary) down in there - add the top collar and keepers - and measure it again. This is your Installed Spring Height. You could slip a spring in the vice and compress it to this dimension. Then compress it more for your cam lift. You'd have a good idea if it's going to coil bind. I do each valve individually, and make my spacers accordingly. You may want to figure them all kinda roughly, that way if you take it apart, any spacer would work with any valve/spring. Or mark them with an engraver as to which spacer was made for each valve/spring.