1. How to remove a sheared off bolt
1) Assuming that the bolt has sheared off due to corrosion, soak the sheared off bolt with penetrating oil overnight. Applying heat can also help to free the bolt, but be careful where you apply the heat. All you’re trying to do is apply enough heat to slightly expand the joint to loosen the bolt.
2) If the bolt head is badly corroded, the socket may round off the flanges, and removal then becomes impossible with the standard socket.
3) Try using a multi-splined socket - use a size which requires hammering onto the bolt to securely grip the bolt head.
4) When undoing the bolt, initially apply a relatively light pressure both clockwise and anti-clockwise to attempt to break the corroded seal, gradually increasing the pressure.
5) With luck, the bolt will unscrew. Without it, it will shear. Onto the next part.
2. Using a stud extractor set
1) Using a centre punch, indent the centre of the broken stud – use one or two solid hits with a heavy engineers hammer.
2) Initially drill the centre of the stud with a small drill, and then increase the drill size until the required sized hole is drilled for the stud removal tool.
3) Important – Ensure that you use the correct sized drill as stated for the extractor set.
4) There are several types of extractor. If it is the fluted type, you will need to lightly tap the extractor tool into the bolt hole, to ensure that it grips. If it has a reverse direction (left hand) thread, screw it into the hole anti-clockwise, so that as you turn it, it will tighten into the hole and remove the stud.
5) Apply more penetrating oil, and gently attempt to unscrew the stud. Apply light clockwise and anti-clockwise pressure as above, to slowly loosen the stud.
6) Once the stud is removed, clean out the thread with some oil and a thread tap.
3. Removing a broken extractor tool
If you’re in the unfortunate position of breaking the extractor tool in the stud, all is not lost.
You can attempt to drill the extractor tool with a hardened tip (tungsten carbide), but this can be difficult and requires some precision. It may also be possible to drill around the extractor to release it – this may then require the hole to be oversized and then repaired with a thread insert, or you may have to take the part to an engineering shop to have it spark eroded to remove it.