Latitude42

My 1998 A6 Quattro Avant with AFC engine got loud under the hood this weekend and I discovered that the righthand exhaust flange gasket is blown out. I've read an older thread on this forum where it's said that, if the studs break off while trying remove flange nuts, the entire exhaust manifold must be removed.

In any other car I've worked on, what usually happens is the stud turns out of the flange when you turn the nut, and you simply replace both the stud and the nut.

Am I understanding correctly from the old forum thread that the studs are permanently driven into the flange, and there is no hope of removing the studs?

CRAZY_RUSSIAN

they do come out. just spray the nuts with some penetrating fluid and let it sit for a day or two, should help

hubturn

Assuming I understand correctly, you are NOT refering to the exhaust manifold gasket but to the connection at the exhaust pipe with the three studs? If so, remember that those nuts are a special copper lock nut. You might consider retapping the three flanges to make putting the new studs in easier, since those threads are going to be very rusty. The studs themselves are most likely interference thread studs, so use new ones and don't think they need to be cleaned up with a die when they don't thread in easily. Lock two regular nuts against each other to get the ability to thread the studs in (i.e. jam nut). http://www.mechanicsupport.com/inter...e_Threads.html
I DO know that the head to exhaust manifold studs are of the interference variety. Further, on my AAH 12v, there is no gasket at the point of question, and I don't think there is one on the AFC.(I've been wrong before.) There is merely a taper fit that is sealed by torque on the three nuts. Clean it up with wire wheel for a beter seal.

Latitude42

Yes, I am talking about the three at the exhaust outlet. This job has been on hold for weeks and weeks. Trying to get to it this weekend.

I did try to turn one of the three nuts after generous application of PB Blaster. Even though I intentionally went gingerly with the ratchet handle, the stud twisted off as if it were taffy. OK, that was only one of the three, the car was still drivable.

I fiddled around with drill-out strategies but I was just wasting time and money. Eventually I went to a junk yard and bought a replacement manifold (perfect match, and only $75) and I need to get the studs out of THAT. My buddy with a decent shop will be helping me with that tonight. I picked up three new studs from an Audi parts counter that used my VIN for accurate lookup. The studs have normal 8x1.25 threads on both sides of the boss.

Today I am picking up manifold studs (against cylinder head) which were also identified at an Audi counter. I'll report whether they have an interference thread on the cylinder head side of the boss. Very worried about breaking one of those off... lights out if that happens.

Latitude42

Poster "hubturn" is quite correct, the exhaust manifold studs specified by Audi parts counter for my AFC have interference threads on the short (cylinder head) end. I do not know if that will prove to be a blessing or a curse when I try to turn the old nuts. Buying replacement studs today may have been nothing more than an education.

Ordered and awaiting arrival of brass jam nuts (recommended by several, including the dealership) before proceeding.

Latitude42

OK, this job of changing out the AFC right side exhaust manifold was finally done yesteray. Observations:

1. Poster "hubturn" was correct about everything. Interference studs are used throughout, and in my 1998 Avant at least there is no removable gasket between the outlet flange and the down pipe to the cat (even though these gaskets are listed and sold for my model with AFC engine). The down pipe has a permanent conical seat in it.

2. A portable acetylene torch outfit is very helpful. A propane bottle and nozzle is nowhere near hot enough.

3. To get the outlet flange studs out of the salvage yard piece, we used a stud puller of the kind that is a chuck with rollers inside that clamp down on the stud. We closed the work in a workbench vise, heated it, and used that thing. They came out like magic.

4. To remove the nuts and studs in the cylinder head, I used a 12mm, deep, 1/4 inch drive (yes, 1/4 inch) socket, very short extension, and a really little ratchet handle. This is the only setup slender enough to avoid interference from the body of the manifold itself. I rounded one nut off before learning this but got the remaining 5 out, easy. The one I rounded required heat and vise grips. Two studs remained in the cylinder head, and they were reusable.

5. Consider carefully just which studs you will install before wiggling in the new manifold. We had all 9 studs installed (6 in cylinder head, 3 in outlet flange) and it was quite difficult to get the manifold in.

Latitude42

And, to conclude, a photo of the deteriorated original. Note that the conical seal (permanent part of manifold) is cracking up, and from the colors it is evident the cat pipe was not meeting square on for quite a while. The three studs must have softened and stretched on their own from rust, heat, and gases.

The miracle stud tool is a "concentric roller stud puller" and from what I can tell vended in the UK only.

Latitude42

Here.

atlasrising

i was replacing the downpipe and cat, broke a bolt. drilled it out, was lucky to get a drill in there, then used a new nut and bolt.