How To: Stripped Spark Plug Removal Procedure
So, you go out side with wrench in hand to do one of the simplest jobs you can, change your spark plugs. Then, tradgety strikes. Your plug socket begins to devour the hex of the plug.
You are now left with a plug with a rounded off hex.
The easy solution would be to ue a bolt extractor like Craftsman's Bolt-Out tools. However, we have limited space to work with in this area, so, chances are, they will not work.
When all else fails, you are going to have to remove the porcelin center of the plug. This can be accomplished by prying, or chiseling with a screw driver. The goal here is not to fully remove the center, just mainly get it loosened up.
Now, start the car. Let it warm up a bit, and then begin to rev it up. It will take a couple tries, but the compression of the piston stroke will build pressure, and push the guts of the plug out of the base. You can now reach down there and CAREFULLY remove the chunks. We don't really want these going in the cylinders. Cranking the engine over a couple turns helps to push the crap out, as does using a shop-vac.
Now, take one of the round screw-type extractors, and back out the plug. You will probably need a breaker bar, and may need the torque levels to be increased. Use as few extensions as possible, because they allow flex, and a loss of power. If worse comes to worse, and you have access, try an impact on the extractor. The hammering action helps to vibrate the bolt lose, and will provide plenty of torque to get the plug out.
Another thing is to not pound inward with the easy out, chisels, or any other tool. It will cause the base to expand in the head, and add to your misery.
After the plug is freed, screw the new plug in by hand to make sure the threads are clean, and to be sure not to cross thread it. Also, make sure to apply a bit of Anti-Sieze to the threads of the plug to avoid this issue in the future.
Now, go drink up... you're going to want to, and deserve it