I'd like to redo the valve seals on the motor I'm swapping into my trooper, but I don't want to pull apart the head since the gasket is in good shape right now. Has anyone done this, and are there any tricks.

Seems to me that I should be able to pull the valve springs and change out the seals without losing a valve down the tube so long as I do each set of valves with their piston at TDC. I've also heard of pumping compressed air into each cylinder while the valve springs are off to hold the valves in place. I'm not sure I'd trust that alone, but the valves can't go far with the piston at TDC.

So, anyone have any input on doing this? I'm trying to get this motor as fresh as possible without cracking it open too far. I'm already swapping oil pans, replacing both crank seals, basically all the external gaskets, so if I could hit the valve seals too that would be as close to a rebuild as I could get without pulling the head. Any tips, ideas, or discussion?

The valves won't move with the air unless you push them down. It depends on how much air you put in and the compressors capability to keep up with the demand. I have no problems with 100psi when doing them.

Here's my little tips/tricks...

Bring it to TDC and before you remove the rocker assy, zip tie the cam to the dizzy shaft. That way you won't have to remove the dizzy and reset it and in the mean time it holds the cam in place while you remove the rocker assy.
I have spare rocker shaft/cam journals that are dis-assembled. I put one on each end of the cam to keep it in place. If you don't have spares you can dis-assemble yours temporarily.
After you've got the dummy journals in place, you can cut the zip tie. *keep in mind that all the valves are closed so you don't have to worry about hitting a valve while you turn the motor by hand SLOWLY.
With the motor on TDC you can do #1/#4 valves. The valves will fall a little but the piston will catch them. *stick a screw driver in the spark plug hole just to make sure the piston is actually up, a little insurance goes a long way*.
Next turn the motor 180 degrees and do the #2/#3 valves.

When your done, reverse the order above... *You can do away with the zip tie deal if your going to change the timing belt at the same time. There is also the nylon rope trick, feed about a foot of nylon rope thru the spark plug hole with the piston at half stroke and as it comes up, the rope will bunch up in the chamber and hold the valves up for you.

oh yeah, Pick up one of those mangnetic tool picker upper things. They really help removing stubborn retainer keepers.

If your budget fits, I'd invest in a set of dual/heavy duty valve springs for later if you decide to throw in a bigger cam.

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I don't have to worry about keeping the distributor lined up, I have to swap my old one in anyway. The donor for this motor is a FI Impulse and its going into a carb'd Trooper, different dizzys. Good tip and something I had not thought about.

I also like the rope trick, simple yet effective.

It sounds like I'm ok with my original thinking of just putting #1/4 at TDC, doing those valves, then puting 2/3 up and doing them. If I run into trouble getting it back together I can always use air to hold the valves up.

Unless something is wrong with the springs I've got I don't plan to change anything. With this motor coming from an Impulse I'll be getting a cam with a bit more duration, and that is about all I plan to do with it for the time being.

I used the rope trick & it worked like a charm. definately use a magnet for removing the keepers and use little dabs of grease to make them stick to the stem upon reassembly.

Just an update, I used the rope trick and it does work slick. Toughest part was getting the retainers to come apart. I had to tap on the spring compressor to get them to let go, and the rope in the cylinder held the valve tight while keeping it from getting damaged. Getting the keepers out with a little magnetic grabber is also a very good tip, that worked great.

When I put things back together I just used motor oil hold the keepers in place. Grease would work too, but I was making sure everything was lubed up at the same time.