Removing steel studs from an aluminum head can lead to some serious
consequences.
Lets say that the head is 356 alloy (just as an example, a common casting alloy)

If it is well heat treated it can have a tensile strength of around 35,000 psi.

If it is not its tensile strength is around 25,000 psi or less.

Thats a drop of almost %29. Other higher strength alloys can drop by as much as
%80.

At what temperature does this happen? About 750 F. Can't you get the heat
treatment back? it could take from 60 min to 4 days at high temps to get it back
to strength.

Aluminum is not like steel. Steel has well known color/temp relationship. Red
hot means an exact temperature. "But I didnt heat it up that much" .... A "red
hot" steel bolt is at over 1,200 F. Kiss your aluminum heat treatment good by.

So you have a stuck or broken plug or stud. You heat up the area (even just the
threads) around it as much as you please. Hey, it came out. Then maybe a few
months down the road you find the threads are falling apart when you take the
part off again. Maybe new head time.

Steel melts at a much higher temp then aluminum. Steel gives a very good warning
of when it will melt. Aluminum on the other hand will just slump. One second you
are happy, the next the aluminum has melted with out warning and its really new
head time.

Watch out when heating our expensive aluminum parts!

Pawling NY

Cars I have: 93 Eurovan MV
                  75 Westy
                  73 Super

Cars I had: 89 GTi 16v
                 87 Syncro
                 83 Rabbit GTi
                 82 Vanagon Diesel (w 83 GTi engine)