Posted by David Sherman on Tuesday, April 12, 2005 at 10:45AM :
In Reply to: Exhaust Manifold Bolt posted by Dave on Tuesday, April 12, 2005 at 9:47AM :
Just the usual rusty-bolt tricks -- Kroil or PB, heat, wax touched to the threads when hot, etc. Best bet on the broken one at this point is try to weld something like a big washer or a bar onto the broken part, apply wax when hot or Kroil when cool to the threads. The heat of welding should break the rust loose. Once in a great while a stuck bolt can be gotten out by drilling with a left-hand drill bit after applying heat and penetrant, and I think there might have even been one time that I successfully used an easy-out, but generally when it gets to the point of drilling, it's going to be a mess. Try everything else first. You need a top-quality bit to drill a grade-8 stud, and it's very hard to keep the bit centered, as it will head for the soft cast iron as soon as it breaks even slightly out of the stud.
Assuming you have studs rather than bolts, at this point I'd first try heating the stuck nuts cherry red, let them cool down, touch a candle to them when they're just cool enough that the wax doesn't burn off, and give them another try with a wrench. I would re-use the studs after this treatment rather than risk breaking them off in the block, if possible.