Broken exhaust flange bolts can be a source of major frustration in any auto repair project. The bolts usually break because of rust and corrosion from the intense heat and high moisture produced by the exhaust. A few options are available if the bolt is broken off above the surface of the exhaust component. However, most of the time the bolt must be drilled out before it can be extracted. Extreme care must be taken to avoid damaging the threads, rendering the component useless.
Spray a liberal amount of penetrating oil on the broken bolt. Lightly tap the bolt from each side to allow the oil to seep in. Spray the bolt again and let sit for 24 hours if possible. Spray the bolt once or twice during the wait.
Clench the bolt in a pair of locking pliers if there is enough sticking out above the surface to grip. Try applying pressure to see if the penetrating oil loosened it enough to remove normally. Be careful not to break the bolt further.
Put on the safety goggles. Using the grinder, grind the bolt until it is flush with the surface, then use the punch and hammer to mark the drill guide in the exact center of the bolt.
Insert a small left-handed drill bit (less than 1/8 inch) into the drill as far down as it will go. This increases the control you have over the bit. Place the drill into the punch hole and begin drilling slowly while adding pressure. Reverse the drill and clean out the shavings every so often.
Increase the size of the bits gradually to increase the hole diameter after each successful pass. Repeat this process until only the threads of the bolt remain. Pull out the remaining pieces or pass a tap through the hole to collapse them inward.
