spark plug removal

my spark plugs are frozen in or so it seems. Would using an air impact wrench be a bad idea to use to remove them a 1979 MGB.

An impact wrench is about the worse idea you can think of.

Lots of patients and good penetrating oil is your only chance. Keep working them out and in no matter how little they'll move at a time until you work them out.

The question is, why did they seize? Are they seized both hot and cold? If you tried with the engine cold, try it hot. Or vice versa.

You can try penetrating oil - but I'm dubious.

I've seen this happen on aluminum heads, but not on cast iron. I had a plug seize once - my own darn fault - I cross threaded it in aluminum and then it corroded. You can put a flex bar on it and apply lots of torque - but the way the plugs are constructed means they will twist the nut part of the plug off leaving the thread portion embedded in the head. At that point, there is no option but to pull the head, drill the plugs and possibly put in heli-coils.

Yes. That is a bad idea.
Look - you're going to break the ceramic part anyway, so go ahead and do it now. Apply some heat and/or use some sort of rust-buster juice, Liquid Wrench, etc. Some guys recommend a home brew of 1/2 ATF + Acetone or whatever, plus tincture of time. Get a 1/2" drive socket and a long cheater - breaker bar. Watch for your knuckles. If you don't bleed too much, all the better. You might need a plug tap to chase the threads.

When was the last time this car ran?

Be careful if/when you break the insulator. The lower section of it is a press fit with some ceramic sealer into the metal body. If you screw up it is possible to drop the business end of the ceramic into the cylinder. If that happens the head WILL have to come off.

Don't go the brute route until you are satisfied that all other means have been exploited and have come up empty.

IMHO this is a good time to try out the 50/50 mix of acetone and atf.

Jack

Sometimes a little clockwise movement first then counterclockwise with penetrant. Patiently proceed with back and forth moves. Progress will come. As Jack says be cautious.

The major reason I've found for spark plugs to seize in a cast iron head was because they weren't tightened enough when installed. Carbon would build up on the threads and lock the plugs in tighter than billy hell. That is always the cause when the plug moves a little bit and stops without ever feeling like it broke loose from it's seat.

CRC sells a chemical called 'freeze out" thats supposed to shrink the item
for removal ...
Anti seize on the new plugs..Put the anti seize on a old plug with good clean threads
and put anti seize on it and run it in and out of every plug hole several times until
you can put new plugs in by hand/rubber hose slipped over ceramic until seated.
Next time you remove plugs you will only need plug tools to break initial torque and
spin out with the hose..

Moral of the story: It's worth using anti-seize.

Billy Hell?? I love that one! I just had this happen, had to do the cheater bar thing to remove 2 of them. I put anti seize on the new ones.

I can vouch for the Acetone/ATF. I had a dizzy that wouldn't come out even after several different hammers, strap wrenches and anything else I could throw at it. But after 5 or 6 soakings of the magic mixture it loosened right up.