Exhaust leak, manifold, stud, and sealer question

[stuartrubin]

In my 1975 124 Spider, carbureted, I have some leaks in and around the exhaust manifold that I would like to (finally) take care of. Specifically, there is some leaking between the engine and manifold, small holes on the manifold, and between the manifold and pipe.

I have bought the two gaskets assuming they would need to be replaced. I also bought four studs anticipating that some may break!

Reading what people have said on the forum, I have a bunch of questions. Thank you in advance for your indulgence!

The 4 studs I got are all the same size, 35 mm. There is some talk that there are different size studs. I have also heard that one of the studs goes through an oil reservoir. Did I get the wrong studs? What do I need?

When replacing the studs, do I need to use some kind of thread-locker or sealer?

Do I need gasket sealer on the metal (or metal looking?) gaskets?

I am hoping to go "cheap" and patch up the small holes in the manifold with some kind of car parts store sealer. (If that buys me a season, I'll be happy). The plan was to remove the manifold and do the sealing on the bench so I could really get a good look at the holes and fills. Is that crazy?

I can't seem to find a blown-up picture of the specific parts (engine, manifold, gaskets, studs, etc.) and their interface anywhere, including the shop manual. I know I probably don't need it, except that I have a suspicion that my car isn't exactly standard. (I'm not even sure all the studs are installed...)

Any other tips? Thanks!

Stuart

[wizard124]

You really don't want to break a stud. Use a penetrating oil on the manifold nuts.
I had a partially stripped hole in the head that also leaked oil. I used a 2 part high heat epoxy to seat the stud. Its permanent as far as i can tell. If yours are tight, i would suggest a threadlock that seals but allows the stud to be removable..
That same epoxy may plug and seal holes or minor cracks in the manifold. May be a cheap fix. Check the mating surface. If it isnt flat., a machine shop can grind it for you. You dont need anything on the gasket.

Why replace all the studs that don't need to be? Asking for problems IMO.

[stuartrubin]

Wizard124, thanks for the tips. As you implied, I am hoping that I DON'T break the studs, but I've read so many stories of them breaking that I bought replacements just in case. (I mean, the cost of the studs were less than the shipping, so I got them when I bought the gaskets.)

I'll check out the high-temp epoxy at the parts store and see what makes sense.

Stuart

[Dawgme85]

The studs should be threaded shorter on one end. Be sure to install the studs so that the end with the shorter threads screws into the head until bottomed out, with oil-resistant sealant (I.e. Permatex or equivalent) applied to provide a good seal. The upper holes penetrate to an oil passage.

[TimpanogosSlim]

If you can get to the holes in the manifold from the inside, versachem exhaust joint sealer may do the job. Thick paste cures to a substance not unlike concrete.

If you strip out the head, the permanent solution is a thread repair called a time-sert. The annoying part is that it's a situation where the tool kit is expensive ($100) but the inserts are pretty reasonable. So the cheap way out is finding a mechanic that already bought the tool kit. Which is specific to the size of insert.

[MikeHynes]

"I have bought the two gaskets assuming they would need to be replaced. I also bought four studs anticipating that some may break!"

You are correct, you may break some studs. The exhaust heat can be pretty hard on the hardware. They may be pretty rusty. But, try very hard not to break one. It'll most likely be a real pain to replace any broken ones. Use lots of penetrating oil and soak it for as long as you can.

"The 4 studs I got are all the same size, 35 mm. There is some talk that there are different size studs. I have also heard that one of the studs goes through an oil reservoir. Did I get the wrong studs? What do I need?"

I may not be able to give you any good advice because my experience is with an '80 FI model. Your exhaust manifold may be different. On the '80 FI there are two different sized studs. Two upper that are roughly 41 to 42 mm long overall. They have about 29mm of thread and shoulder. The three lower studs are longer, they have about 37mm of thread and shoulder. These should make reasonable replacements:
http://www.midwest-bayless.com/p-22550- ... 0-new.aspx
http://www.midwest-bayless.com/p-22549- ... 5-new.aspx






"When replacing the studs, do I need to use some kind of thread-locker or sealer?"

Only the two shorter top studs can leak oil, they should have some sealer applied to the threads. Don't use epoxy.

"Do I need gasket sealer on the metal (or metal looking?) gaskets?"

No.

"I am hoping to go "cheap" and patch up the small holes in the manifold with some kind of car parts store sealer. (If that buys me a season, I'll be happy). The plan was to remove the manifold and do the sealing on the bench so I could really get a good look at the holes and fills. Is that crazy?"

Crazy? Maybe. Optimistic? Very.

[TimpanogosSlim]

I get the being cheap part but is the idea to put it off until you can afford headers?

An exhaust manifold isn't THAT much money. 1975 would be an 1.8, right? that's a common manifold.

[TimpanogosSlim]

The more i think about it the more i think thermal expansion may prevent any leak repair in the manifold from lasting more than a few hundred miles.

Short of welding anyway. And welding cast iron is difficult.

(edited for clarity)

[geospider]

to jump on an old post.
I have just gone through this: after the rebuild, had a small leak at what looked like the 2nd stud from the front of the motor. Pulled it out (wasn't that tight), used some permatex high heat thread sealer (white) and a new stud. Actually then leaked more. Now, this stud is longer going into the head. Is that an issue?
I do have the old, stock studs. any ideas? is there a better sealer?

When everything else is just great, this is a pain.

thanks,

geo

[Minlest]

Hi! Did you ever get to the bottom of this? I've got terrible leaking and white smoke coming from the manifold after installing an exhaust system that created too much backward pressure, and now I can't stop the leaking even with exhaust removed entirely.