How To: Broken bolt extraction

[rob love]

I thought I would share a method I use to quickly remove broken bolts or studs. The best bet is, of course, to heat bolts and studs red before attempting to remove (and breaking ) them, but that isn't always possible. In this case, I was working with a leaking gas tank on the museum's C15TA, so there was not a lot of heating going on before removal.

My method is a slight variation on the method used by a lot of welders, where they weld a nut onto the broken stud, then, as it cools, you work the nut and back the broken stud out. Most will use an arc welder for this...I like the MIG. Problem is, when you are welding down the bore of the nut, you might not get the best penetration onto the broken stud.

I select a washer either the size of the stud or one size larger. In this case, the broken bolt is actually slightly recessed into the hole...that is fine. I weld the stud to the washer, then weld a much oversized nut to the washer/stud. As it starts to cool, you start to work it back and forth slightly, then it will come out as an assembly, leaving the threads intact. I use high heat on the welder so as to get good penetration into the stud.

Now don't get me wrong, there are still times when you will have to drill and re-tap, but overall, this method has worked well for me again and again. It is especially good on situations where the fastener is broken off inside of a casting such as an engine block or transmission housing.