Cuz then I was changing the seals on my 420sel I tried it. I put 120psi into the chamber and then tried to compress the spring (had the piston at TDC for insurance) and its a good thing I did. The keeper was wedged into the spring cap hard enough that I was able to overcome the air pressure and open the valve. If by chance the keepers had let go and the valve had opened at the same time the valve could have dropped into the cylinder. Its just not worth the risk of dropping a valve into the cylinder. Putting the piston at TDC for each cylinder only takes a minute.
Have you ever changed the seals using air pressure to hold the valves? Has anybody? I have never made it work. I tried it twice. Maybe I needed something like 175 PSI which I did not have.
Just my opinion.
I got too many cars!! Insurance eats me alive. Dave
78 Corvette Stingray - 3k
82 242 Turbo Volvo - Manual - 270k
86 300e 5 speed manual - 210k
87 420sel - 240k
89 560sl - 78k
91 420sel - 205k
91 560sel - 85k
94 GMC Suburban - 90k
97 Harley Davidson Heritage Softail - 25k
00 GMC Silverado 1 ton 30k