What white pasty material would be found inside a cylinder head valve.

Sodium?

I forgot to mention that this white pasty substance explodes when it comes in contact with H20

what white pasty material would be found inside a cylinder head valve.

It is most likely just white grease used as a sealant. Double check with your airport mechanic.

oliver321 : i forgot to mention that this white pasty substance explodes when it comes in contact with H20


Definitely Sodium filled valves then. Probibly exhaust valves, right.

Used to promote cooling of the valves in instances where EGT's can get high, I.E. in the automotive world, with high performance or turbocharged engines, In aircraft as a safety measure.