Every machine shop guy and tech I have ever talked to including my father who has 35 years experience as a mechanic. Heat up some aluminum and tell me if it doesn't expand. Since it expands (swells) it will constrict inside a hole.

It depends on how bad a condition the plug is in and what kind of removal tool you are using. The ones I use that allow more torque use a small pilot hole. I have had the best results with those.

Once the hex of the plug snaps off the only thing remaining is the thread. The hole thru the threaded part is quite large already. Use anything smaller than the proper size ez out and it will likely drop into the cylinder.

I have more than 35 years experience and aluminum does expand when heated. Aluminum housing are heated when bearings are pressed in or out. Sometimes a manufacturer specifies heating the head to remove or install valve guides. Your information is incorrect.

* Chas H is correct. With heat, the aluminum hole will present a slightly looser fit, not a tighter fit. That's why you apply heat (torch) around a threaded hole to work a seized stud/bolt out of it.
* The problem with replacing plugs in a hot alloy head is more of a caution than a problem. It's more likely to damage cyl head threads with overtorqueing when the threads are hot. Overtorqueing is still a problem cold but the threads are less likely to damage.
* Needless to say, the best way to tighten plugs is with a torque wrench. And the most accurate torque wrench scale in this case would be an inch-pound scale (where 18 ft-lbs would, for example, be 216 inch-lbs).
* But if you don't own an in-lb, or even ft-lb, torque wrench, work with a cold engine, put a drop or two motor oil on the plug threads and tighten the plug until you feel the crush-ring (if the plug has one) collapse. If the plug just has a tapered seat (and no crush ring), and you don't have a torque wrench, you'll just have to approximate it and tighten it until it feels gas-tight. Unfortunately, leaving a plug too loose causes a another, different set of problems.

My bad. I must have been misunderstanding what folks were telling me:(

Don't beat yourself up over this. ;)
For many years, Vehicle Manufacturers were very adamant about changing plugs on aluminum heads when they're cold.
I believe part of the problem is, if there is any amount of combustion residue ( hard carbon ) on the end of the threads of the plug, you have a tendency to pull the threads out of the head.
A warm/hot engine ( softer threads ) increases this risk.
" Heli -Coil " time.;)
To each his own. ;)

spark plug broken
 

Hey guys.
I got the spark plug out with a #6 ez-out.
The advantage I had was the plug sheared off just below the nut, so the whole core and electrode came out in one piece. No need to drill.
I treated the "thread body" with penetrating fluid, tapped the ez-out lightly with a hammer to get it to bite and then gently used a 1/2 inch drive breaker bar to crack it loose.
Worked slick.
Went from a $1400 head removal estimate down to $8.95 and some hair loss. Whew!
Again thanks to all who offered their help.
C'

I'm glad it worked out well!