How to Remove A Rusted Exhaust Manifold bolt
Every mechanic has had a few of these. There isn't any one single trick that will work on all of them, but there are some simple principles that will get you out of the situation if you just don't lose your patience. If you strain on the end of the wrench or socket handle and the bolt just doesn't budge, and you feel that if you pull just a little bit harder the damned thing is going to break, STOP. If you break it, you've just made your problem worse.
Two words come to mind in the battle against seized fasteners, lubrication and heat. Lubrication sounds pretty simple, and it is, but there are a couple of things to keep in mind: first, all the WD-40 in the world won't do much good if it can't get to the actual contact areas that are involved. That means that you don't just spray a ton of the stuff on the fastener and then grab the wrench. If you take a magnifying glass and look closely at the problem, you'll notice that the rust has grown up around the interface where the threads of the bolt meet the female threads. I like to take a very sharp pick, and scratch that bulge of rust away, remember, patience is a virtue. Work slowly and carefully, working your way around the entire circumference of the bolt, spraying a bit of the lube on the area as you go. Sometimes you can't get all the way around, just get as much as you can get to. Then give it a good spray and start over, you'll have missed a few spots, remember, PATIENCE. Get the point of that pick right into the little groove bertween the threads and work it back and forth. Give it another little squirt of the WD now and then.
Then, with the box wrench or socket, try working the bolt back and forth a bit, that's right, try to tighten it. then work it backwards and forwards a few times, with a little squirt of the magic stuff now and then. Don't round off the head of the bolt, and DON'T use so much force you break the bolt. If you're lucky, it will start to move a bit, if so, you're home free, just keep working it back and forth and you'll notice it goes a bit further each time. A few more minutes, more WD,and you're done. Didn't that feel good?
If the trick above didn't get it loose, it's time to bring out the big guns, the torch. WARNING: If your cylinder head is aluminum, you must be VERY careful to only heat the steel bolt, and not the cylinder head! If the area is reasonably clear of flammable objects, and you have access to a good torch, a little heat will often loosen the grip of the rust enough to get it moving. Remember, the pick is your friend, always prepare the threads with the pick FIRST. I use an oxy-acetylene torch to quicly heat the bolt up to a nice cherry red color, then hand the torch to a helper and quickly put the wrench on the head of the bolt and gently try to turn it each way. Work it back and forth just like the WD technique, and as it cools off a bit, use the penetrant. Once you get it to move a little bit, you're home free. If you don't have access to oxy-acetylene, it can be done with a propane torch, but it's a lot trickier. The secret to this technique is that you are trying to heat ONLY the bolt or the nut, if you heat up both, it isn't as effective. You want to make one expand and break the rust bond. Once that bond is broken, the penetrant can get in between the threads and work it's magic.
If you get impatient and break the head off the bolt, one of two situations happens: either there is a bit of the bolt sticking out, or there isn't. If there IS enough left to grip with a pair of vise grips, proceed as above, using the vise grips instead of the wrench, remember, use that pick FIRST! If there isn't anything sticking out, things just got REALLY interesting.
Now it's time to break out the drill and check the selection of drill bits.