While I was removing a donor slant 6, both of the exhaust-manifold-to-pipe studs snapped because some genius decided to use red loctite on the nuts. Is there any way to easily fix this, now that I've installed the engine in the car? My plan was to drill the studs out and replace them with bolts, and my second, much stupider plan was to use two C-clamps to hold the exhaust together.

If it was me, I'd pull the manifold and take it to a machine shop to get those broken-off studs out. Attempting to drill them out yourself is a recipe for disaster, as the bit is going to want to wander into the softer cast iron, thus ruining the threaded holes. A machine shop can clamp the whole thing down in a mill, and get those out without anything close to a mistake.

Replace the studs with stainless studs and brass nuts, and the problem goes away.

Roger

C- Clamps, lol

I'm not so sure about the SS studs/brass nuts bit. You've got 3 very different metals at play then....lots of opportunities for seizing/corrosion etc. Plus, finding SS studs will be a little tricky for the average dude.

If the manifold has a flat face on the back side of the hole - something a bolt head can seat on - I'd drill the studs out (properly on center) and use steel through bolts with steel nuts. Once you've done that, you'll never have to worry about it again as removing them, even if rusted and seized completely, is no more difficult than lighting up the torch.

The other problem is that I haven't removed the manifolds from the engine yet. The reason for that is, while removing the manifolds from a different slant six, I broke both of the long and unnecessarily thin manifold connecting bolts off on THAT exhaust manifold. The exhaust pipe studs are intact, but it's got one of the connecting bolts still rusted solid into it.

Is there any way to take the studs out of the manifold easily? If so, I could just replace the broken ones with the good ones.

Probably not. They're most likely rusted in pretty well. If you do get them out, it'll involve plenty of heat and penetrating oil. But I'm guessing you have nothing to grab on to to help unthread them. I'm wondering why you didn't address the issue before installing the engine in the car? At least you would have had better access etc.

The answer is because I'm an idiot. My second plan involved drilling through the studs sideways, heating the manifold around them, and jamming something through them to use as a T-handle.

Well, if there is enough to drill through sideways then there is enough to grab with a pair pf pliers. You could heat the manifold carefully then loosen them up by turning. You need a pair of pliers that are curved jaw that tighten the more you turn them. Like Channellock 414 pliers. Or a brand new pair of Vise Grips that still have really good teeth.

Regarding using brass nuts: some aircraft piston engines use them on exhausts. When you finally get the studs out or re-tapped or re-drilled, how about using high-temp (nickel) anti-seize on everything, and good quality split lock-washers for security?

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"Louise", a 1976 Dart Custom project, (now sadly reverted to being just an "organ donor" to our other project Darts.)

I was going to get a heat gun to heat the manifold, but then I remembered - It's an exhaust manifold. I can just run the engine to heat it up. Also got some all-metal locking clamps with ring adjusters to try the first stupid idea. I can tie them to the car with wire and that way even if they fall off they won't pose a threat to anyone behind me.

Highly likely that will do anything. You are going to need a torch.

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2 Mopars come with Spark plug tubes. One is a world class, racing machine. The other is a 426 CI. boat anchor!

12.70 @ 104.6

Yea, the manifold won't get hot enough by running the engine (especially at idle/no load). Though, running it would help pre-heat the manifold to lessen the burden on the torch and to reduce the odds of cracking the manifold due to uneven heating.

I don't see any need for special locking provisions once you go back together....I sure don't have exhaust flanges loosening up. I'd just use a plain Home Depot split lock washer and some anti-seize on the threads. I use the Permatex kind. Here's a picture of me as soon as I open the jar:

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Doo Ron Ron and the Duke of Earl are friends of mine.....
https://www.youtube.com/watch?v=uX8Nj8ABEI8

What I meant was that I'm trying my first stupid idea. With the locking pliers.