Exhaust Manifolds

Removal and Installation

Removal - L4 models

"I tried to remove the Oxygen sensor, but instead of coming loose, the exhaust manifold broke."
I had to replace my exhaust manifold on my '84 for the same reason. It was actually very easy, just time consuming. If I remember correctly there are 9 bolts holding the exhaust manifold (em.) to the head. Those came out fairly easily, just remember to use penetrating oil before breaking off the bolts! The hardest part of the whole thing is removing the two bolts connecting the em. to exhaust pipe. These two where rusted so much I had to get a hacksaw blade in there to cut them in half. If you have to do this be extremely careful to avoid puncturing the pipe. In my '84 there was a good amount of space to swing a wrench, but to get at the em. to exh. pipe bolts use a breaker bar and an extension. If you have someone to help you they can locate the socket on the bolt while you lay under the car. That way you can swing the ratchet 360 degrees. Don't worry about breaking these, you will have to replace them anyways, and the broken piece will be in the em. which you will toss anyway. Remember to disconnect the battery or the extension bars may have a chance to hit the connectors on the starter. I hope this is detailed enough, good luck.

From: Richard Simmons

Removal and Repair - V6 models

A few recent messages from people with exhaust manifold questions and problems may find this of interest. To these guys, feel free to contact me if you need more details on this experience of mine.

The engine ticking noise that once was, is no longer. This engine sounds like it's a day old now. The removal of the obstructive metal in the manifolds seem to have added a slightly better sound, along with a small but noticeable increase in horsepower as hoped. I am thrilled with the outcome.

I would NOT recommend doing all this work for the hp increase alone, but it is certainly worth it, if the manifolds are off for other reasons.

As I wrote in August, my engine had a sewing machine sound to it when accelerating. Someone on the net thought that it could be an exhaust manifold leak. Listening closely to where the noise came from, I felt this could be my problem. After I removed both manifolds, I inspected them and their gaskets, finding numerous leaks. Four of the six ports had some sort of leak. Black soot made it easy to diagnose. One port was cracked where the stainless pipe mates to the steel foot. Three ports leaked through the gasket, the result of loose bolts. There was also a crack in one manifold near the crossover pipe fitting. All the leaks surprised me because there was no indication of leakage, other than the engine ticking noise. Engine operation seemed fine. I could not see any soot without first removing the manifolds, so inspecting them prior to removal revealed nothing.

I decided to repair the old manifolds, rather than buying new ones. After all, I planned to mill out the obstructive material, then reinforce them by welding ring beads where the stainless pipe meets with the steel feet. I had the cracks re-welded as well. A welder did all the work on both for $30.00 total, much less than $170.00 for one new manifold. I gave him the manifolds bolted to hardwood to minimize foot planarity problems. Also, I soaked the feet in muratic acid to strip off the rust, insuring a good weld. When I got them back from the welder, I touched them up with a belt sander to perfect their flatness.

Another comment... I was the guy asking the V6 owners if their manifolds glow red in the dark, upon a cold startup, like mine did. Well now after all this work, my manifolds still glow, but somewhat less. If this is so, it may be due to the reduced restriction, resulting in lower underhood temperatures.


...assuming you have manifold cracks and/or leaks, and have had all the recalls done already.

Your engine should sound and drive better (much better in my case). Removal of the restrictions might lower underhood temperatures as well as give an additional eight to ten horse power increase.


  1. Q: How much of the exhaust system, other than the manifolds themselves, do you have to remove? Or can you just unbolt the manifolds from the rest of the system, leaving it in place?
Do not buy new manifolds, re-weld the old ones. Save your money.
Remove the built-in restrictions in the manifolds, and weld them where the pipe meets the feet.
If you are doing this yourself, plan on some down time. It is not an easy or moderate job at all. (was not for me anyways)
Use only the high temp manifold gasket, as specified by Pontiac.
Plan on reusing the bolts on the difficult side. Buy new ones for the trunk side. The trunk side bolts are different, and tend to snap, so take it easy when loosening these.
The air conditioner compressor will have to be unbolted from the engine. This does NOT involve Freon removal, just lowering the unit onto a frame member. The lower bracket with 2 bolts will have to come out. The upper bracket with three bolts will have to be removed, but NOT detached or even loosened from the compressor itself. Removing the battery will gain you access to these. A ground strap on one of these bolts must be reattached when done. The top two bolts also hold the black bracket that works with the dog bone. If this bracket loses it's alignment with the engine, loosen the one bolt that is near the dog bone bracket. It helps.
While the battery is out, check the battery tray for rust, and use Rustoleom Rusty Metal primer and a good black paint, two coats each.
When shopping for the grinding attachment, make sure to get a cylindrical style grinding piece with a longer than usual 1/4" shank. I have found the best one for this job at an Ace Hardware. It spins so fast with the router that you get sparks, like a regular grinder. Wear good eye and ear protection.
If you are planning to grind out the welds at the steel feet, then I recommend taking it to a welding shop FIRST, before you start cleaning it out. When you get it back, the new welds will have penetrated through the stainless tube, and will need re-dressing. I also bought a 3/4" diameter, coarse wire brush for the router. Using it when you are done grinding, will remove any imperfections left over. It polishes it up beautifully. When shopping for these tools, make sure that they are rated for the speeds your router spins at. Total cost for them should be less than $12.00.

When you attempt to reinstall the air conditioning compressor, you may experience what I did. The top bracket has 3 bolts to the engine, Right? When I removed them, the black bracket that is behind the air conditioner bracket, shifted slightly, just enough to give me a lot of grief. I tryed and tryed, and tryed (and tryed) to realign the air bracket, and the top 2 bolts with the engine with NO SUCCESS. I went crazy! Everything appeared to line up perfectly, but in fact, the DOG BONE bracket moved so little that I could not get the bolts to thread in.

If this happens to you, don't waste any time. Loosen the one big bolt that holds the two pieces of the dog bone bracket together. This will allow the self centering action needed to attach the upper air compressor bracket.

Prior to reinstalling the manifold, inspect it for flatness. It must be flat to seat flush with the engine head. I used a belt sander to touch up the 3 feet to perfect the flatness. To minimize flatness problems from welding, give the welder the manifold bolted to FLAT hardwood, or better yet a steel block. On my other, now sold GT I just gave the two manifolds to the welder, and got them back with the feet at all different angles. I did a lot of belt sanding back then. Don't make that mistake.
A: The rest of the exhaust system stays in place. You remove 6 bolts per manifold that attach them to the engine, and 2 bolts per manifold that attach them to the crossover pipe.
  • Q: Someone else mentioned removing the deck lid to gain more access to the engine from the topside. Did you have to do this? Can you remove the manifolds from below, or do you have to go back and forth from=20 below the car to above?

    A: Removing the deck lid is well worth the effort. Don't be concerned about removing it because it REALLY IS simple to do. Four bolts, one connector and the grounding wire to the deck shield is all there is. It takes about five minutes to do, and saves a lot of hassle. Reinstalling it is just as easy, EVEN aligning it to the car. It may be possible to remove the firewall/front side manifold entirely from below, but don't torture yourself. I worked from both top and bottom. Car ramps work great for this.

    The manifold by the trunk is done from the top only. If you don't break any bolts, it will be very easy. Removing the cooling tubes, and alternator heat shield makes the difference. Disconnect the battery too, so you don't short power to ground at the alternator with a wrench.

  • Q: You mention obstructive metal in the manifolds that you removed. Is this something that is placed in the manifolds, or is it just residue from the manufacturing process? How hard is it to remove, and how did you go about doing it?

    A: There are two areas of manifold restriction. The 1st is as follows. The obstructive material DOWN INSIDE the manifolds is the result of low cost/high tolerance manufacturing methods, and has nothing to do with the integrity of the manifold. One of the three ports is fine, but the two that T-Junction into the main tube have the obstructions.

    The 2nd source of obstruction are the weld beads that are located right at the entrance points (3 for each manifold).

    I bought a 1/4" shafted grinding wheel at Ace Hardware for about $4.00 to do the job. I used my high speed router to grind out the obstructive material in both areas, but I suppose you could get away with an electric drill. When you remove one of the manifolds, and examine it, everything will become clear concerning "what to do".

  • Q: Did you have a general welding shop do the work, or was it someone who does a lot of specialized welding (someone who had worked with this kind of thing before)?

    A: I went to a generic welding shop. I asked them to use their standard stainless welding rods. They knew what I was talking about. When you get them back from the shop, you will want to dress up the inside again, a little. Maybe taking them to the shop before you do any grinding would be best.

    Your concern of having a shop do all this for you is valid. I've heard of $500.00 for replacing one manifold. I don't believe they would be as careful as you either.

    If you DO snap a bolt, it is a REAL HASSLE to drill out the stud, but it IS possible to, without removing the engine or other major disassembly.

    One more thing. There is a recall on the manifolds. Make sure that your car has none outstanding. If your car has not been in for this, you are in luck. Your problem will be resolved for FREE. Call 1-800-PMCARES.

  • Q: I must have changed my manifold gaskets at least 10 times in the last 3 years. They would always start leaking soon after I installed them, that ticking sound is very familiar to me. Never knew there was a "high temp gasket" , who makes it and where can I get it? Is it one of those genuine GM parts only available from the dealer?
    A: The high temp gasket can be purchased by other sources as well as Pontiac. I bought mine from a NAPA parts store. They look different, and are easy to identify, even when installed. The standard gasket is more flexible, and the high temp one is more rigid. To identify the right one, look at the gasket material that holds the three sections together. You can see it spanning in the air, between the manifold ports. If the spanning gasket material is near an inch wide, and is strait (without any bends), then you have the wrong gasket. The correct gasket has a few strain relief bends in it, between ports. The material width is about a half inch. My guess is that there is much more metal making up the high temp one.
  • Q: I noticed that extra metal inside the manifolds on the last 2 ports. I thought this was there to equalize the back pressure on a 3 ports. The one furthest away does not have any restriction. I tried to grind this away once but the stainless steel was too hard.
  • A: All I know is what I've read on the net, and in Fiero club news letters. The restrictions are not a good thing. They are simply horsepower robbing, the byproduct of sloppy manufacturing methods.

    I have had great success removing the material with a high speed router with a grinding wheel attachment. Both the router and wheel were rated at 25,000rpm. Using a drill spinning at 1000rpm, or using a file, would certainly take longer.

  • Q: I bought a rotary file to use either in my drill or the router. I tried a grinding wheel in a Dremel tool, but the wheel didn't last long. Do you think this will work? I've seen the ones at Ace but I didn't get one because of the experience I had with the Dremel tool grinding wheel.
    A: I have never used a dremel tool, though I sure would like one for Christmas. All I can tell you is that the grinding wheel I used did wear down, but it lasted the duration of the project. If your manifolds have more excessive material then mine, then buying two may be necessary. The one I used was around 3/4" in diameter, and 1 1/4" long, then adding the shaft length.
  • Q: The dog bone you refer to, is this the one on the rear or does your 86 have one on the front also? I only have the one on the rear. In either case, I have noted your advise and will use it this weekend.
    A: The 86-V6s are identical to the 88-V6s when talking dog bones. Mine is located on the passenger side, between the trunk and the thermostat, directly above the alternator.
  • Q: The only thing I was going to do to the manifolds was to remove the excess material inside them. The only welding beads I can see are all on the outside. Should I be looking somewhere else?
    A: YES! Just to clarify, hold a manifold such that you are looking inside one of the 2 T-junction ports. You see the slots in the main tube. The slot material is the MAIN obstruction, of which I know you understand. The 2nd obstruction is present in all 3 ports. Put your finger inside any of the three ports, and feel for a raised welded bead that is located right at the opening, where the tube itself is welded to the steel foot. I have measured the holes in the engine, and compared that dimension the the inside diameter of the manifold tube. They are about the same. The obstruction is the weld ring at the edge of the hole. Depending on the bead size, you could have a "DECREASED" diameter by as much as 1/8" to 1/4". I have found it necessary to first remove the ring bead, to increase the opening large enough to get the router chuck inside to attack the slots. Remember my previous message. First take the manifold to the welder, and then grind out the material. You want the welder to ADD outer ring beads between the feet and the tubes, in all three areas. This is to reinforce the feet because you are going to weaken the inside welded areas.
  • Q: I was planning on putting two gaskets on, is this a mistake? My local Pontiac dealer has a set in stock that I'll get in about an hour. I was going to use a new one and an old one in hope of sealing off any leaks.
    A: I would not recommend using two gaskets, new, used, or whatever. It is most important to focus on flatness to count on a good seal, and not filling in gaps with excessive gasketing. You could be reliving the nightmare all over again, if you blow a weak gasket.
  • Q: I plan on using my belt sander to take out any high spots. Did you use a belt for metal or for wood? I know I have some 60 grit wood belts, what do you think?
    A: I used a FINE to MEDIUM grit belt that is good for both wood and metal. If you have a lot of material to remove, start with coarse, and work down to fine. Try what you got at home first before you buy anything.
  • Q: The A/C compressor; I still have not been able to loosen the pivot bolts and if I do, then I won't be able to tighten them again once I have the compressor in place. How do you get the A/C belt tight again? I don't have any room between the compressor and the firewall for a wrench. Advise needed here.
    A: I assume that you have the compressor attached to the upper bracket, but resting on a lower frame member. Tighten up both bolts that attach the two together. The compressor WILL pivot, even when the two are very tight. It is designed that way. There is never a need to loosen them in the first place. Like you say, it is impossible to access these two bolts when the bracket and compressor are on the engine. You will have to use a huge screwdriver as a lever when tightening the belt. It will take some strength, but it does work. The lower bracket has a string of slots, that help when using the screwdriver.
  • From: Ron Dittmer

    Having done a couple of these before on my own cars, may I offer some advice. The large more or less flat shield goes between the block and the gasket, then the manifold itself and then a half round heat shield goes over the manifold. This later piece is a result of the recall a few years back. Most owners including myself never had a problem with exhaust leaks until this recall was done to us. In my case, my manifold not only started leaking but as a result of a very poor installation by the dealer, most of the bolts backed out of the head causing first the gasket to burn out, then the manifold to crack, with the noise getting louder each time. This happened within a few months of the recall "fix". If you decide to fix this yourself, or even pay someone else to do it, do yourself a big favor and remove all the original bolts/studs holding on the old manifold and replace them with 8mm stainless studs, nuts, and lock washers all the way around. Also install the studs and nuts with locks using locktite red, then torque properly. This will help your fix stay fixed for much longer.

    From: Pat Dobyns

    [Top] | Online Service Guide Main Page