Broken bolts cause many problems during a routine repair. Even after several attempts you may find they are all but impossible to remove. When bolts break off inside an aluminum block, a few tested methods are often used. These methods protect the soft aluminum from additional damage. However, they require skill and patience.
Things You'll Need
Apply penetrating oil, such as Mystery Oil or WD-40, to the bolt head. Allow it to drip around the bolt and eventually work into the threaded portion. Let the oil work for several hours before attempting to extract the bolt.
Tighten a pair of locking pliers until the teeth fit securely around the remaining part of the bolt. Clamp the locking pliers around the bolt and turn them. Repeat this process several times. If it does not work, go to the next step.
Heat up the bolt and a small portion of the surrounding aluminum metal with a propane torch. Hold the torch a few inches from the bolt so the flame touches only the bolt and about 1/4 inch of space around it. Wait until the metal turns red-hot. Remove the torch and allow the bolt and surface to cool.
Attach the locking pliers to the bolt once again after it is sufficiently cool, after about 10 to 20 minutes. Turn the broken bolt until it comes free. If this is unsuccessful go to the next step.
File down the top of the bolt with a metal file until the surface is perfectly flat. Place a bolt removal bit on this flat surface. Turn the bit until it locks into the bolt. Twist the bit back to the left to turn the bolt and remove it from the metal.