Broken bolt removal and thread repair

Broken Turbo Bolt Removal

Today I am going to show a little trick I have learned for removing broken exhaust bolts. Pictured is a turbo off of a customers rig that the turbo was literally falling off of. It had broken 3 out of the 4 turbo mounting studs.
Sometimes you can get lucky and extract these bolts by drilling a pilot hole and using a bolt extractor, or by using a left hand drill bit. In my experience exhaust bolts are usually so rusty that they wont come out easy and there is a very good chance that you will break off the extractor or the bolts are so hard that a standard drill bit wont cut through them. I have found this true especially if they are heated with a torch as a means to try to extract them. This seems to harden the bolts to the point that a standard drill bit wont cut.
Enter the arena: The annular cutter. Pictured is 3\8 annular cutter. These work differently than a standard drill bit. Instead of two cutting flutes, these have 4 very hard cutting teeth. These are hollow in the center and are basically a mini hole saw. The advantage is the hardness of the bit. The bits are harder than even an over hardened exhaust bolt and will cut it like butter. The downside is they will only cut to their max depth. Which in this case was perfect because the bit was slightly longer than the thickness of the turbo flange.
Broken turbo bolt
First grind the bolt flush and smooth and center punch the bolt as centered as you can get it.  . Then start drilling. You wind up with this:
Bolt hole drilled out
Important note: On something like this I like to stuff any port that I don't want metal shavings in with rags. Also it is very important that you get the bit as centered as you can. So take your time when center punching the bolt before you start drilling.
Here is what is left of the bolt. Like I said the annular cutters work just like a hole saw.
Piece of broken bolt after drilling

Next use the supplied tap in the helicoil kit and tap out  the bolt hole. After that install the helicoil and your all done. Your repaired part is now ready for installation.

How to install a helicoil
Hopefully this helps someone out there spending hours trying to drill out a bolt. There are other methods out there but this is a shortcut I use to save some time. Also if you aren't comfortable with this most machine shops offer this service.