flyingscott

So while replacing my subframe I wanted to drop the cats to get better access to bolts and removal. I attempted to remove the 3 nuts from the bottom, cat end of the manifolds.

I found that on the drivers side flange, one stud was already missing (appears to have rusted off or someone didn't bother to replace it), another was hanging on by a thread and the other wasn't much better. That explains my exhaust leak. So all studs on my drivers side are now gone.

And on the passeneger side, one stud was rusted and is now gone, the others are still in pretty good shape.

Now I have to fix it, what should I do?
A) My vw mechanic friend says to drill out the studs all the way through and drop a bolt in as a replacement. What would be a good replacement? Would grade 8 be better for the heat?
B) How easy is it to replace the studs? I'd imaging that with the amount of corrosion I have already encountered, extracting the stud would prove very difficult.

Is there a gasket I need to order that goes in between the flanges of the cat and the manifold?

Either way, I have some work to do.

1993audi90

You must be in the NorthEast somewhere. What was the deal with the subframe part number?
I've had this issue as well. I did it on the car with a long *** drillbit. Since you need to do all three, though, I'd pull the manifolds off--you'll have to anyway-- and source some replacements from AZ, TX or CA. The nuts I think are copper or copper coated. There are gaskets on the Head side and flange end. Drilling those is going to be a PITA, You can try heating it red hot and using vise grips on the stub that is left. If you can get all three out, just buy new studs. If there is nothing left to grab onto, on one or two of those you wont be able to screw a bolt in from the top. In that case, you'll have to run all-thread up the bottom and put a nut up top because the OEM threads will likely not hold.
See why just getting new manifolds would be easier?

1996
Exhaust Manifold
Audi A6 LH,V6,100 OFF+RDY TO SHIP,STOCK NO. #00705048 #00705048
$30
Auto Part Locators USA-AZ(Tucson) E-mail 1-800-221-2749

A quick search on car-part.com revealed one side in AZ for $30.

flyingscott

Yea, the 90 is from NH and I'm in MA. I got the old subframe out and haven't put the new one in yet, sitting on jackstands till I can get to it next weekend.

I was afraid I'd have to take the manifolds off, I'm worried about messing with the studs on the head, just one more thing to go wrong. How difficult is it to remove the manifolds? I've read its a pain with the engine still in the car, but I've got no other way. I suppose there is too much in the way to deal with it on the car.

Any source on studs, nuts and gaskets? I've searched but I can only find the exhaust manifold gasket to the head.

Why can't I drill through and drop a bolt through? I'm away from my car so I can't look at it to see if there is something in the way.

Jeff-AudiUSAParts

The studs should be N0445122 for .94 each, nuts N90200201 for 2.03 each, and manifold to head gaskets 078129589 for 24.38 each if needed. I didn't see manifold to pipe gaskets or seals used on a 95 V6 engine.

On using a bolt dropped from above down, that might not work if the curvature of the manifold has a bend in it that wouldn't allow you to do that. I'd think if you were going to run into that it would be on only one of the 3 holes but it still is a problem. Sometimes the head of the bolt might be too wide and may not seat flush with the surface of the manifold in that area too.

If that would work it would save you from maybe having to buy new manifolds. Good luck!

duanevw

When I did my 95 90qs 2.8l arc engine, there were no gaskets for the down pipes where you have to do your new studs.

On the a4 2.8l arc there was a gasket but it was a different type of end on the down pipe.

So no gaskets for your 3 point flange where your doing your new studs or bolts. I had my engine out and dad spent time withe torch for head and a drill and thread chaser to clean threads and installed new ones which he matched up locally at a industrial bolt place.

Duane

flyingscott

Thanks guys,

Jeff, I sent you a pm with a couple questions on parts.

I wasn't sure on the gasket or not, but thanks for the affirmations.

I'm very concerned about removing the manifolds from the head. I'm worried that I'll shear or mess up the studs going into the head, is this a good possibility? Anyone have experience replacing studs in the head? Would that require removing the heads?

I think I'm going to buy a couple of used manifolds and replace the studs so I can have them ready to go in while I'm working on it.

1993audi90

I had some donught gasket which may not have been OEM from the CAT to manifold.
I wouldn't worry about the manifold to head issue, the shops scare you with that to try to jack up the cost. Aluminum to steel--I've heard all the supposed horror stories. But I've pulled apart a few engines here in PA and never had a problem with manifold to head bolts. Make sure you use the right size socket and make sure it is square on the bolt. You can reach them with a flex socket/long extension going through the hole where the inner tie rods go through the apron. With the CATS out of the way it should be easy...

flyingscott

Thanks for the reassurance.

I'm going to go ahead and order any extra parts I may need, including new nuts and studs for the head side of things. Anyone know the part number for exhaust manifold studs in the head?

Any other parts I should have in case something goes wrong?

hubturn

It may be difficult to remove the exhaust manifold from the head while still in the car. 12v.org mentions that when removing the head, leave the exhaust manifold on. So good luck with that. As to the studs. The exhaust manifold studs that project from the head are tap end studs. This means that one side is threaded shorter than the other, and that there is a space between with no threads. Additionally, and this is the really important part, the tap end side threads are different from the other side. The tap end side threads are interference threads. They may look the same, measure the same, and a nut may thread on the same, but they are NOT the same. They are different enough that when threaded into the head, they slightly bind and create enough friction to prevent them from backing out due to vibration. Even so, some high temp thread locker would probably be prudent. You will immediately notice that they do not thread in easily. Stifle yourself from wanting to "clean up" the stud threads with a die and thus defeating the whole purpose. (I understand the paranoia of stripping out the aluminum head stud holes.) The same goes for the three studs at the other end connecting to the cats. Drill out the old if necessary, retap them and put in new studs. There you are dealing in cast iron and it is less worrysome. Order all new studs and the copper nuts, which are the squeezed/lock variety. You'll see it when you get them.

flyingscott

Thanks for the info hubturn. I've read about the interference threads while searching the forum.

Does anyone know the thread pitch of the studs in the triangle flange? I'm trying to get a tap on order but the only info VAG Cat gives me is M8x30.