[jim_howard_pdx]

If you have a lot of miles on your engine, I expect your blow by has increased, you may have poor cylinder sealing at the rings, or worn cylinder walls. Many engines will have some pitting on the valve faces, and poor sealing on the valves to boot.

So I would pull each plug, fill the cylinder with a bunch of thick but flexible string, and then compress the cylinder until the string or rope compresses against the combustion chamber. Now you can pull off the locks and retainers, and change out the springs.

This is an "ol guy" trick we used, before compressed air was discovered.......he he he......

But again, I would do this anyway because I have had new fresh engines that still dropped the valve with high air pressure in the cylinder.

The rope might end up saving you time and distress.