what is everybody using to change there v-springs when the heads are still on the motor? we are talking 440-1 heads and a roller cam profile spring rate (about 210 s.r.)

http://chucker54.stores.yahoo.net/ben2pivaspto.

or this
http://www.summitracing.com/parts/PRO-67461/Application/?prefilter=0

I make an air chuck by welding a fitting to a dismantled spark plug.

You still want the piston all the way up as you may have to press against it a bit after tapping with a brass hammer to unseat the locks a bit.

There is a couple of tools that will do this but the best one is the lever one that pivots on the rocker shaft. The screw clamp ones are really only good to use on single or stock type springs.I made one of these lever ones back in the early 80's before you could buy them and if you have a little bit of imagination you could make one to.I have changed springs between rounds using it,they work really well.
If air is a problem I myself bring the piston up to TDC and use a chunk of TV cable wire in the spark plug hole and position it under the valve you are working on.It will keep the valve high enough up to remove and replace the keepers.Hope this helps.Good Luck

The lever arm and air pressure in the cyl are really
all you need... other than a mallet and a magnet to
pull the locks out .... pull the rocker shafts and
the plugs... screw in the air adapter in to the cyl,
smack the retainer with the mallet to loosen the locks,
then use the lever arm to push down the retainer
and use the magnet to pull the locks... reverse the
procedure after you change the spring... after you
put the locks in place tap the stem with the mallet
to make sure they are seated