Actually, this is possible but won't be easy. You will have to make a special tool to compress the valve springs without removing the head. What you will need to do is:
1. Get a steel rod (we'll call it "rod A") about the same diameter as the camshaft journals. Cut it short enough so that it will fit exactly from end to end in 2 of the cam caps. You will tighten the cam caps down on this rod to hold it secure when compressing the springs. This rod is used as a fulcrum.
2. Weld another rod (rod B) perpindicular to rod A approximately 1" long (it will point away from the valve when using the tool). This is used as a lever to get leverage against the spring.
3. Weld another rod (rod C) perpendicular to rod A but on the opposite side of rod B. Rod C and rod B should form a straight line, but rod B should be angled upward so that it sticks up high enough so that it will clear the cyl head when using the tool. The length of this rod must be just short of hitting the valve retainer when rod A is bolted down in the cam caps.
4. At the end of rod C, you need to weld on an adaptor that will compress the spring without getting in the way of the valve itself. It could be in the shape of the fork or a doughnut or whatever, but it needs to be positioned so that when you lift up on the lever (rod B) with rod A secured in the cam caps, the adaptor compresses the spring.
Using this tool, you can remove/install stem seals, springs, and keepers relatively quickly with the head on. Sorry I don't have any pics.
1. Get a steel rod (we'll call it "rod A") about the same diameter as the camshaft journals. Cut it short enough so that it will fit exactly from end to end in 2 of the cam caps. You will tighten the cam caps down on this rod to hold it secure when compressing the springs. This rod is used as a fulcrum.
2. Weld another rod (rod B) perpindicular to rod A approximately 1" long (it will point away from the valve when using the tool). This is used as a lever to get leverage against the spring.
3. Weld another rod (rod C) perpendicular to rod A but on the opposite side of rod B. Rod C and rod B should form a straight line, but rod B should be angled upward so that it sticks up high enough so that it will clear the cyl head when using the tool. The length of this rod must be just short of hitting the valve retainer when rod A is bolted down in the cam caps.
4. At the end of rod C, you need to weld on an adaptor that will compress the spring without getting in the way of the valve itself. It could be in the shape of the fork or a doughnut or whatever, but it needs to be positioned so that when you lift up on the lever (rod B) with rod A secured in the cam caps, the adaptor compresses the spring.
Using this tool, you can remove/install stem seals, springs, and keepers relatively quickly with the head on. Sorry I don't have any pics.