Stuck spark plugs

[Dave Michael]

This happened to me on an Alfa Milano. I put all the other spark plugs back
in, ran the engine till it was hot, then removed the stuck plug no problem.
The thermal exp. coeficiant for Al is 12e-6 in/in/F, for steel its 6e-6
in/in/F. For a 1" dia hole and 100F increase in temperature, the hole
diameter will grow by 0.0012", and the plug will grow by  0.0006". The
difference is enough to maybe allow you to break it free.

Hope that helps a little,

Dave
90 200 qa
87 alfa milano (75)