Disclaimer: I’m not a mechanic and a mechanic might be horrified at learning how I did this. Most will suggest removing your engine head but I’m too cheap. If you’re cheap too, and you don’t mind the risk, read on.
Prologue: I was replacing plugs on a 2001 Buick Century and things were going well. The spark plugs were quite stiff to remove, but nothing was too crazy. Then I got to one that wouldn’t budge. I kept the socket square, put in a bit of elbow grease, and..
Mine snapped at the metal part. Left inside the motor were the threads and porcelain middle. To get an easy out in, I would have to drill out the center, and potentially get chunks of porcelain stuck down in the cylinder, where they’d make a real mess. Here’s the trick on how to punch that porcelain center out without getting porcelain everywhere: turn over the motor and let the cylinder compression do the work for you. I turned the key over and within 3 rotations, I head the porcelain center POP out of the body. This left the metal threads and base of the plug inside the cylinder. I used a #5 easy out, 6″ 3/8 extension, 1/2″ male to 3/8″ female adapter, 16mm 1/2 drive socket, 1/2 drive, plus a 2 foot iron pipe, in combination to get enough torque. I tried many unsuccessful combinations, but this one gave me enough torque to break that plug free. Remember to center the #5 easy out and the drive line or else you might slip or put torque on the wrong angle to the plugs.
I also sprayed the plug threads several times with liquid wrench penetrant to free up the threads.
The #5 easy out was the perfect size to use in combination with the spark plug. It gave me plenty of torque with absolutely no slipping. So, if you’ve snapped that spark plug in half how I did, you might want to look into this method of getting it out.