So Fix it

Removing Exhaust Manifolds

Work on enough engines and youre bound to run into at least one exhaust manifold bolt that would sooner snap than back out of the block. While any monkey with a cheater bar could simply yank and hope for the best, a wise mechanic will have the foresight to know that proper removal now beats drilling the block later.

The Basic Problem

The exhaust manifolds arent just the hottest part of your engine; they and their bolts represent a junction point where several very hot parts of differing composition come into contact with much cooler components. Because metals expand and contract with changes in temperature, according to their molecular composition, the nuts, bolts and studs holding manifold to engine block tend to seize up. Rust -- excess oxidation as a result of constant heat -- is another contributing factor, but heat seizing is usually the primary one.

Pretreating the Bolts

Pretreating the bolts is the simplest way to ease manifold bolt removal, and may be enough if the bolts arent seized too badly. Spray all of the manifold bolts -- those on the cylinder heads and those connecting the manifolds to the exhaust pipes -- with a liberal amount of penetrating oil. Spray along the manifold-to-engine interface and use as much as you need. Respray the manifold bolts two or three more times within an hour and allow them to sit overnight if possible.

Work the Bolt

Attempt to remove each bolt after youve given the penetrating oil time to work. If the bolts will move a bit, work them back and forth while constantly lubricating the bolts threads with oil. If the bolt comes halfway out, turn it so it goes back in. The oil on the higher threads will lubricate the thread holes in the block, easing removal. Apply the appropriate pressure to stuck bolts, but if they wont come out, then its time for a bit of heat.

Heating the Bolt

This is a last-ditch effort short of cutting or snapping the bolt, but its one that often works. Using an oxy-acetylene torch set on medium -- the flame about half yellow and half blue -- heat only the head of the bolt till it just begins to glow red. Have someone nearby hold the torch while you attempt to remove the bolt, in case you have to heat it again. Do not attempt to use penetrating oil on the hot bolt; itll just flash and flame away. Try working the bolt back and forth.

The Last Resort

If the bolt still doesnt come out, youve got two options: you can cut the bolt-head off with a grinder and cutoff wheel, or keep applying pressure till the bolt snaps. Of these, the latter is the more dangerous because the bolt could well shear off flush with the block. At least decapitating the bolt leaves you with the option of repeating the listed steps and trying to remove the shank with a pair of vice grips. If you get this far, try grinding a small flat on one side of the shaft to help the vice grips get purchase.

Prevention

After finally getting the manifold bolts out and removing that stubborn lump of cast iron, you may be tempted to say to yourself: "Well, this is the last time Ill ever have to do that again." Not so fast, there, Speedy. Youd be surprised how quickly manifold gaskets can blow out after installation, and then youll be cursing the thing anew. Even if you think that youll never have to remove these manifolds again, do the car or engines next owner a favor and apply a bit of anti-seize compound to the bolt threads before reinstallation. Anti-seize is cheap insurance, and using it is something for you to feel smug and canny over afterward.