Exhaust Flange Studs Stripped

[ghaegele]

I just got the winter cover off this year and am looking forward to an early launch. One of the jobs this year is an exhaust leak. It is coming from the joint between the exhaust flange and the manifold. When I replaced the manifold after a rebuild a few years back one of the studs started pulling out of the manifold as I was tightening the nut. I stopped immediately and pretended I didn't feel the threads give. (Anybody else done that?)

My strategy worked until the end of last season when a lot of exhaust was filling the cabin. I now need to retap that thread to an oversize. Has anybody had this problem and know off hand what the thread sizes I'll be working with? Is there a larger size stud for this? Will I have to drill out the flange to accommodate a larger bolt if there is no stud? Any other tips are appreciated.

Thanks, Greg

[Will Jacocks]

I think no matter what way you go, you will still have to drill it out. I would thread it and install a stud with some kind of a thread lock, maybe one of those kits that you can jb weld some new threads in. Or rethread for a larger bolt. I thought MMI sold a kit for that, but didn't see one.

[Al Schober]

Check into a HeliCoil. I install them myself, but if you're not comfortable with drilling and tapping, have a shop do it for you. One the helicoil is in place, you can you a bolt or epoxy a stud into the helicoil.

Al

[Will Jacocks]

That's the term I couldn't come up with, thanks! :cool:

[jstaff]

Or use a threaded (keyed) insert...

[jpian0923]

Very useful information for the A4 owner.
http://www.cncphotoalbum.com/atomic4manual/partslist.pdf


The original bolt is Cap screw 3/8-16x1" so a 7/16 would be the size up from that. If you truly have stripped the threads on the manifold I'd imagine all you would need to do is tap for 7/16 without drilling. But if you stripped the threads on the stud, I think just a new stud would work for you.

In either case, to me, the flange gasket isn't enough protection from exhaust leaks. I sealed mine with light coating of Permatex Copper.

[Maurice]

Hi Greg,

I would remove the manifold and the hot exhaust in one piece. Take it to a mechanic or machine shop and have them remove the old, retap, and put new studs in there for you.

Since it's been a few years it might be a good idea to build yourself a new hot section as well..then you won't have to bother with it for a few years and you know what you have.

All the best.

[hanleyclifford]

Don't forget the stud repair kit available on this site at the on line catalogue.

[ghaegele]

Thanks for the replies.

It's clear the threads in the manifold stripped and not the stud. I used a new stud and it happened as I was tightening the nut. I knew what I was feeling.

I don't know if there is space in the manifold to insert a HeliCoil or other keyed insert(?). Anybody done this? Is there enough metal there?

I really don't see this as a fix that requires taking the manifold to a shop and replacing the hot section. Maurice, a few years isn't that many for an exhaust. (And how do you it's been a few years? You're making me feel creepy now.)

If I retap to the next size (7/16?) can I get a stud that will also still fit into the flange? The Moyer repair stud for the block won't work.

Finally, since the manifold is hollow, can I either get a 3/8 SS bolt out that thread hole from the inside, or get a nut onto a 3/8 threaded rod from the inside? Then hold it in place with some JB Weld if needed for reassembly?) Don't know if I'm making myself clear. The manifold is still connected to the engine and I'm having trouble visualizing what it looks like.

[Maurice]

Hi,
You said it was on there a few years in your first post. I think the going rate for a black iron exhaust is about 5 years...then crud inside or corrosion seems to push us have another look at it.

Anyway, I did mine last Sept and it was 4 years old. I was crawling under the cockpit and pulled on it to move myself...it cracked...rusty. It would have lasted longer had I not pulled on it.

I removed the manifold and hot section in one piece. Fortunately had oxy /acetylene to remove the old studs and picked up a couple at Nova Automotive (they buy parts from MMI). Then ran a tap through the threads of the manifold and flange.

Bought the plumbing parts in black iron (had to use one Galvanized 45 degree elbow because I couldn't find a black iron one and it stunk for days). Built exactly what I had, wrapped it with heat absorbing material and reinstalled. It took me about 3 hours.

My point with the machine shop was so that you wouldn't end up having to buy extra tools that you may never use (or find when you need it) again. If you took it out and had it retapped, the flange also will have to be done if you go over size. Normally, to have the studs removed and tapped it should cost about $20 . Those guys have lots of little tricks for situations such as yours.

I did mine myself and it costs me about $60 total if I remember correctly...not a major job if you have the gear.

[ghaegele]

Maurice, the exhaust was done even a few years before the rebuild. If the black pipe doesn't last more than 5 years I'll scream. I hate that job. The last hot section replacement lasted many years, but that was before all our pipe was from China. Anyway, I'm not replacing it unless it crumbles in my hands. This year I'm sailing.

I've had the manifold off a few times on more than one A4 and haven't had a problem getting the studs out (that's the nice thing about the SS). Pretty sure this one won't be a problem as that's the whole issue! Anyway, I guess I'll see what I have when I get the manifold off. Still hoping I can get a nut on the standard stud from the inside.