[Jamesp]

One of the few things I did not take apart on my Box engine, but I'll assume it is typical. To get it apart you'll need to pressurize the cylinder and pull the valve back until the pressure seats the valve. That is what will hold the valve in place so you can work on it. Then you have to depress the disk at the top of the spring. Chances are it is jammed over the valve keepers (two little half shells between the disk and the valve stem). To break it free I put a large socket on the disk and tap the socket with the hammer. Take care the socket can not contact the valve stem. As the spring is broken chances are the valve keepers will fall out when you do this, so expect it and have something in place to catch them. Now that the disk is no longer jammed you have to push it to compress the spring while not moving the valve and while maintaining access to the area where the keepers are so you can pop them out with a dental pick or small screwdriver (assuming hey did not fall out already). As you have the new spring there for this procedure you put in the new spring, put the disk back on the valve stem, depress the disk to reveal the keeper grooves in tsh valve stem, re-install the keepers and release the disk allowing the valve spring to expand. You're done!

You'll find having the proper tool to do all of the valve spring compressing will be critical. I'll bet someone reading this has insight into what works best.

Needless to say, if the valve does not seat the head needs to come off.