1970 exhaust manifold heat stove

[broughj]

The studs on my driver side big block manifold that are used to attach the heat stove have been ground off flush to the casting boss.  I want to try to machine those stud pieces out without destroying the thread in the manifold. I'm going to use a Vertical mill and expect to have to drill them out completely.  Are the manifold end of the studs 1/4-20, 5/16-18, or something else.  Any other ideas how to get them out without machining?

Thanks,

John Brough

[anlauto]

1/4-20

[wes473]

You're a brave soul,
Soak in pb blaster or similar... An old farm trick is to heat cycle and pb soak days ahead, and pray.
-Dremel grind a flat for a screw driver.
-After you find and drill on center as best you can I'd try to easy out as much as possible.
-In theory is you're handy at brazing, you could insert a steel rod into the drill hole and braze it then have something to spin...(similar to welding a nut onto a stuck bolt of larger size)
-If that dosn't work you can step it out to tap drill size(you can use an endmill to recenter).

Once you go down this road I'd be prepaired to use a keensert and redo the threads in the end, hope the on center drill holes were good!

Or find a good manifold ;-)