Off topic--drilling out broken bolts/studs tip
 

Sometimes a broken stud or bolt won't come out by welding a washer to it and then a nut to the washer. And I have usually had a hard time getting it center punched right in the center to drill, so the drilled hole was off center. I figured out that using a die grinder with a small ball tip, I could carefully grind a dimple quite accurately in the center of the bolt, then center punch and drill. The ground dimple makes it much easier to center punch in the middle than the rough surface of a broken stud/bolt and the drill bit stays in the dimple rather than jumping around. Cheers.

Re: Off topic--drilling out broken bolts/studs tip
 

Another method is to use a gasket as a template on a thick aluminum plate, and drill a pilot hole in the precise center of the hole on the plate. Bolt up the plate, and while using the pilot drill bit in a hand drill, graduate up in size until the broken bolt is thin enough to unscrew itself. I used this method with an exhaust bolt without removing the engine.