Have only had to do it twice myself.. Drilling it out with increasing size bits has worked well for me..

Take your time and of course, getting the hole centered is the trick..

Had a badly rusted thermostat housing bolt break off in a cylinder head.. When the last bit was run down in it, it just kissed the outer edges of the threads and was able to pick out what was left of the bolt with a sharp tool..

Ran a tap down to clean the original threads and they were reusable..

2000 4Runner,V6,Auto,31's, Sliders, Skids, On-Board Air, Air Shocks
Related Interests: Welding, Ham Radio, Road Tripping (Blue Highways), High End Video/Audio Systems