When dealing with a car with aluminum head(s), what is the proper way to extract a broken sparkplug?
A couple ways to go about this, depending on the exact situation:
If the ceramic stem is broken, and you can still fit a deep socket on it, go with that. If the nut itself is stripped so much that you can't get a socket or an open-end wrench on it, or if the nut is broken, you should try using pliers to remove the spark plug. You could also try something like a deep socket Craftsman Bolt-Out bolt remover if it is stripped. Another option would be to drill a hole in from the top, going straight down, and using a screw extractor to remove it.
Pictures to help: Craftsman Bolt Out:
Before doing anything else, get some penetrating oil. Reducing friction in the threads will dramatically reduce the amount of twisting force required to remove the stuck plug, making the job way easier & reducing the chance of making things worse (i.e. breaking off a screw extractor!)
Follow the instructions on the container, or just spray around the threads, and let it sit. Tapping with a screwdriver or wrench will help it penetrate and break up oxidation.
One more option:
If you tried taking the spark plug out of a hot/warm engine and the plug broke off between the
lug-flats and the
lug-threads (both non-technical terms), you may be able to use a screw driver or chisel to gently tap the remaining portion out.
When your engine is hot, the spark plug holes are compressed due to the expansion in the metal making a much tighter seal. When the engine is cooled, the engine head metal contracts to its natural position, so the plug threads will not be stuck in the threads.
All of the tension holding a plug into the head of your engine is held by the lip of metal around the
lug-flatswhen it is compressed by tightening the plug into the head. If the plug snapped between the
lug-threads, there is no longer a lip holding compression on the spark plug. In other words, it is just sitting in there with little to no resistance keeping it from turning out. A screwdriver or chisel tip can be pressed against one of the jagged edges and used to turn the remaining spark plug back out.
Take a careful look at this special situation before you go the extractor route. An extractor in inexperienced hands can ruin a head.
I'm sorry I don't have pictures.
One other tip that you may wish to try if there is no way to get a socket on it, two long screw drivers down the inside of the remains of the plug so they nip up against the electrode tip and try turning it out that way. I've personally had success in this scenario using this technique on a Renault.