engine submerged in water

[albirk]

If it is broke off flush try welding a washer on the bolt(5/16 bolt 1/4 washer) and then weld a nut on the washer I  do this about 5or6 times a day about 9 out of 10 will screw out if not get a center drill bit to start your hole they will not walk on you like a regular bit will get the hole started and drill with the biggest bit you can watch the bolt if you can see it if you see it more stop put in a left hand bit and it will screw right out.       good luck

[Al_Smith]

You can drill them out .A little secret is "step drill " them .in other words use a small drill bit then increase the size a tad untill you get to just about the size of the miner thread diameter  .Often times if you're real lucky the threads will back out like a coiled spring .

There's a little trick which only comes from practice of drilling out studs without ruining the thread base .You can burn them out with a torch too but that's another subject all together .