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Exhaust manifold removal


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I've been told that on an engine that hasnt run for years, you should heat the bolts a little and then pry off gently in order to avoid breakage. Whats your input?

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I've seen posts where the recommendation is to heat around the bolt, throw cold water on it, and repeat a number of times.

Also, another good idea is to soak it with penetrating fluid for a week or so. If this does not succeed grind the top of the bolt

off and then you will have the stud to deal with when the manifold is off. All in all, not an easy jobgininatu

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Well,

you have to be careful with the water- the idea is to thermally cycle bolts (expand and contract) which might work only trouble is if you heat near red hor you are near the temperature which result in forming a very hard and brittle material when you quench it the microstructure changes thus more chance to break. SO if you do the heat and cool keep the temperature at 200-300F max. Heating red and cooling slowly goes wrong too this time you soften the bolt too much with same end result (breaks)

If you are talking about manifold to pipe studs if they don't feel right they will break so cut off and leave enough to grab with vise grips the manifold can then be removed and heated red (cast iron structure is not affected in the same way as steel-which is iron with very very low carbon content while cast iron has very high carbon content) AROUND the stud hole when all it cherry red stud will back out like butter.

Other wise you will have to drill in that case cut bolt flush and carefully center and drill to a step below thread size and clear out with a two flute tap.

If you are comming off the engine v-8 is easier than inline engines, v-8 usually spin out if you can get on the bolt head. Sometimes you will require a metric size below that you force over the rusted head size.

For any manifold if it doesn't come off realtively easy be sure you check for hidden bolts like under the center- especially true of in line engines.

try and work evenly from center out to ends.

If you break a stud in the head be careful when drilling not to go into a water jacket or oil passage, generally studs bolts are threaded in about 5/8" Some cars have sutds going into water jacket from factory but I don't think Buick did.

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I just took mine off my 73 Centurion last week. I had sprayed them down with PBlaster penetrant for a week but it really didn't matter. They snapped like toothpicks. So I cut the broken bolts down close and drilled them out and re-tapped all of them. Took me about an hour to drill and tap. Just be careful when your drilling, you don't have much play. I had to drill the holes in my header flanges a little bigger to get the holes to line up. But, seeing that big 455 engine on the stand with its new enamel paint and those big chrome headers makes it worth it. Good luck.

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I just had the passenger side exhaust manifold gasket changed today as it was leaking badly. Took it to a local speedshop/mechanic. He had to heat the top 4 bolts and grind the manifold a bit to get rid of some pitting. Charged me $113 to do it, $13 parts and $100 labor. Definetly worth the money.

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If you drill out the bolt, what sort of bit do you use, a titanium bit treated for metal? I would imagine so but not sure. I may be in the same situation get my manifolds off. Need to get at the head and it won't come off for the manifold being in the way.

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Actually, I had no problem drilling with a $20 11 piece zirconium coated craftsmen drill bit set. I used three bits - 1/16th to get it started, 3/16th, and then 5/16ths. The stock bolts should be 3/8-16 (16 threads per inch). You drill to 5/16 to tap 3/8. Use something as a cutting oil as you tap, doesn't really matter what it is, I used the left over power steering fluid. Engine oil works just as well. Dunk the tap in the oil and apply steady pressure as you twist the tap in. When you feel the tap start to bind, back it out and rinse off the cast iron chips on the tap in a small container of your cutting oil and keep doing this until you have tapped through.

About 10 years ago I worked in a machine shop and learned the skill of tapping. Be careful, if you break the tap in the hole, it can be almost impossible to get out because taps are typically hardened to 62 rockwell.

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