We change a lot of valve valve springs at the dyno. There are many ways to do this.
If you are using the air method you will want an air regulator on the hose. You want just enough air pressure to hold the valve shut and not so much that the air pushes the piston down. Start with about 15 or 20 psi and turn up if needed. The piston will stay up better if the piston is exactly TDC.
Remove the rockers.
You will probably have to break the retainer loose from the locks as they can get stuck. There may be other ways but this is how I do it. Take a small hammer, plastic or brass would be nice but steel will work if you're careful. Tap straight down parallel to the valve stem near the outer edge of the retainer. A few taps should do it. Listen as you tap for a change in sound. You can come back to this step and repeat if it's still stuck.
Plug all the places where a lock could fall into the engine with shop rags.
Install the compressor tool and compress the spring. If the valve wants to open you either need a little more air pressure or the retainer and locks are still stuck.
Push the retainer down past the locks use your fingers or a small magnet to retrieve the locks as you are pushing down.
Let the spring and retainer up and remove from the engine. Replace the seal. Put the spring and retainer back on the head.
The next part can be tricky. When you compress the spring to replace the locks you may notice the retainer is closer to the valve stem on one side than the other. Try to put the lock in the side that is closest to the stem first. Let up just enough to hold that lock in place while you place the other lock oppsite it. If the lock catches on the retainer when you let up just move it over a little and try again. Push back down just enough to slip the last lock in place without the first falling out. lol. Visually compare to another valve to make sure all is in place properly.
hope this helps.
