Would like to change the exhaust manifold on a 580k. The bolts that hold the manifold to the head are badly rusted. If they break, how are they then removed? drill out and hope you keep the threads? The bolt is harder then the casting, small diameter, would be hard to drill out.
It will really depend on how bad they are in there, as what you see on the outside isn't necessarily what's going on inside with the threads, but that can also work the other way where they don't look that bad and are just pure fused rust inside. I had a couple on my 580C head that were broken, one that already was when I got her and another that broke on me when removing the exhaust manifold with no real warning sign it was going to. I just built them up a shade with the welder, tacked on a washer, then welded on a nut and they both came out with a couple smacks on the wrench. If you can get them to turn at all, then gently turn them right back before trying to continue backing them out, as that could help break them loose, and if they do break loose get some penetrating fluid in there to help them come the rest of the way out. Really kind of have to get the feel for when they will start to bind up and you're having to get on them too much, but then on the flip side sometimes they will just let go before you know what's going on as it's just their time. If in doubt though, or you haven't done any welding or have a big enough drill press to attempt drilling it out perfectly square, just have a machine shop get them out for you, as you don't want to mess anything up that could be done with the proper setup. I wouldn't even consider attempting it by hand unless you had a mag drill, and even then pulling the head would just make things easier to work with. That head removal with new gaskets and such will be far cheaper than having to get yourself another head if it does get all knackered up in the process of trying to remove them, in which case you'll be pulling it off there anyway.
start soaking them down with one of many penetrating rust busters for a day or so, then apply lots of heat and if you break them, follow above advice to weld a nut on them to remove..
I would cut the nuts off with a ox/acty. torch to get the manifold out of the way. Then there is good access to getting the studs out. Weld a nut back on and try them. Smack them with a hammer real hard a couple of times first. Turn them firmly as if to tighten them, then remove them. Always has worked for me.
That first picture isn't nearly as bad as it looks. When you weld a nut onto something like that, the bolt expands against the casting, the hot metal deforms and shrinks when it cools. The pressure crushes any rust and the bolt usually comes right out unless the weld is terrible, then you get to try again. The weld won't stick to the cast iron so that's not an issue usually. The only broken bolt I couldn't get out turned out to be stud welded to the plate. I tried that one many times because welding a nut had always worked well in the past???
If you have exhaust manifold bolts that are really crusty, there is another option if you think they're going to break. Try them all and see how many you can get off, no more than 1/8 turn I'd say before they pop and spin. For all the stuck ones, cut the heads off with a torch, now you can remove the manifold, you have taken the tension off the bolt, give the remaining stud a rap with a hammer and apply penetrating oil then vice grips. I've not had one fail to come out though you might end up rocking it back and forth until the oil gets in deep enough. You can also weld a nut on the stud and use a small impact gun to rattle the bolt to freedom. Also, often you don't have to drill it out, but drill a hole of decent diameter, welding tip on a torch to heat that bolt up near cherry, when it cools it'll shrink in the bore, then gently try to tap it with a punch and apply an extractor.
Ok, I should have posted a pick, some of the bolts no longer have a head, will wait till fall to try as I us the machine during this time. I assume if I muck it up I can take the head to a machine shop for repair.
if you were closer I could get them out for you
If the bolt heads broke off near flush with the manifold, you can put a bigger say 1/2 inch nut over the end of the stud and hot mig wire weld up the top of the broken stud until it fills the nut as well, now you have a new head.