Do you use a socket and hammer it on the retainer to unlock the keepers and retainers before trying to disassemble the springs on the heads? If not try that first I have several differnt valve spring compressors including a Snap On and one with the air cylinder on top that you described, it will work on most roller springs (under 800 lbs so far) if I knock the retainers and keepers first with a socket and hammer I am looking to buy a better one like in your picture and from Mancini