"X" in combustion chamber

[Dick Steinkamp]

Has anyone else seen an "X" cast into a combustion chamber? Does anyone know what it signifies?

Here is my #4 combustion chamber...

 

[Farrell In Vancouver]

That marks the spot to put the ex in

 

[BILL WILLIAMSON]

"Maybe" it's an XPRIMENTAL head???
Bill Xpert

 

[Dick Steinkamp]

Maybe where the pirate treasure is buried?