Exhaust Stud Questions/Advice sought

[BenjamminsFiat]

Hey all,

One of the projects I'm going to undertake will be switching my stock exhaust manifold and downpipe to a 4-2-1. Not only is this supposed to help the engine breathe better, but it'll also give me a chance to take care of the massive oil leak I have at the exhaust studs currently.

I have the manifold and downpipe thanks to an awesome Fiat guy here in Houston, and now I'm just looking to get anything else I need to do the job. From what I hear, this job can be absolutely awful if you're not prepared... plus I'd like to be reasonably prepared should things go wrong.
Here's what I have so far:

• 1) Exhaust Manifold - CHECK
  2) Downpipe - CHECK
  3) Exhaust Studs - What size/material should I get and where should I get them? I'm thinking I'd like to just replace all of them while I'm in there. Does that sound like a good idea? I know I run the risk of them breaking off and me having to drill them out. I've also hear of people moving to bolts instead of studs? Any pros/cons of that approach?
  4) Manifold to Downpipe studs - Same as above, but these are the ones that connect the manifold to the downpipe. I don't have any at the moment. Where can I get some with long nuts
  5) My exhaust hangs really low, and when i glanced under the car, it looked like the hanger at the transmission was bent. Might need a new one of these too

Any help/advice the gurus can give me would be awesome and appreciated.

[SouthSwedeSpider]

Sorry no answers but similar question. I'm also interested in the exhaust studs (and the intake studs as well):

• - dimensions/materials,

• - where to get them,

• - could they all be replaced by bolts, and last and probably most important,

• - the best way to seal those intruding into the inside of the head ?

I read somewhere that brass or copper nuts should be used if using studs to facilitate removal of the manifold the next time, but I fear such nuts will be too soft. I don't want to risk stripping the threads once its all in place. Any opinion on that?

I'm planning to use all new studs/bolts when changing my head, and just leave the old ones in the head to be removed.

[manoa matt]

There are 5 threaded holes in the head on the exhaust side, three lower, and two upper. The two upper holes are drilled and tapped into the cam area of the head and subjected to oil, hence why you frequently see an oil leak there. The upper two holes must be filled with studs or oil will leak out. Clean the threads in the head and stud, then apply RTV or pipe dope prior to installation to prevent the oil from leaking past the threads and burning on the manifold.

Studs vs bolts: If you use a stud, the stud is steel and threaded into the aluminum head. The stud will thread in and have a good deal of thread engagement with the aluminum head. The manifold is put on, and a nut is used to retain it. When you tighten the nut, the steel nut is acting on the steel stud threads to provide the clamp load. Some of the clamp load is taken between the stud and the head, however that load is spread out over many threads and the stud is not turning as it exerts this force. If you over tighten or strip the threads, you will only strip the threads on the stud or nut, both easily replaceable.

With a bolt, as you tighten the bolt, the steel bolt threads are engaging the threads in the aluminum head. As the bolt rotates and tightens, it pulls on the threads in the aluminum head and has a greater chance of pulling the threads out. If the threads in the head get damaged, its more costly to fix.

Studs will provide a better and more even clamp pressure with less chance of damage to the head, however they make removing and installing the manifold a bit more difficult. Studs and nuts are also less likely to work themselves loose compared to bolts.

Regular steel studs should be fine if you place some anti-seize on the threads before installing them into the head, and anti-seize on the threads prior to installing the nuts. A step up from that would be to use steel studs with brass nuts. But really, if you do it right, how many times are you going to remove and replace it?

To remove studs you simply place two nuts on the stud and tighten them against each other. Use a wrench to remove the stud while turning out on the lower nut. Installing studs is the same, but install using the top nut.

I may have the exhaust hanger bracket that bolts to the trans bell housing, I sold one a while ago, so I'll have to look if I have another.

[BenjamminsFiat]

Thanks so much Matt!

EXACTLY what I was looking for. It's possible that I'll start work this weekend. I'll try to take lots of pics. The information regarding studs vs bolts makes so much sense. Applying force while turning the bolts does sound like a recipe for stripped head threads.

Just a couple more specific questions:
1) What size are the studs if I do want to replace them with something better? (I want it to look really good after I'm done). I'm thinking length, diameter and thread pitch

2) What should I use to clean the threads once the existing studs are out? Would just a chemical work, or are we talking a well lubricated tap?

3) Let's say once I get in there, I find one of the holes in the head is stripped. What's my next move then? Helicoils? is it possible to take care of that in situ? From the angle, I can tell it wouldn't be easy but would it even be worth trying?

Thanks again! If you find that bracket, I'll buy it from you.

[manoa matt]

1.) Thread pitch is: M8X1.5 Length of threaded portion that screws into the head is around 15mm. The un-threaded shank portion of the stud depends on the exhaust manifold, but probably around 10mm. The exposed threaded portion will depend on what washers, lockwashers, and nuts you install, but probably around 15-20mm.

2.) A thought that occurred to me was: The passage/void in the head where the two upper studs are screwed into is under the camshaft carrier/box/tower. Even if you suck the remaining oil from the cam box via a turkey baster, there still may be oil in the void area around the stud. When you remove those two studs, oil may come out. Can't say how much, maybe a few drops, maybe a tablespoon, but no more than a few ounces. Be prepared to catch it. You will need to let it sit a while with the stud out so the remaining oil can drain out. Spray it with brake parts cleaner or acetone and maybe twist up a paper towel to clean it out. Don't spray too much cleaner in the hole as it could wash away oil from the tappet buckets and the next startup could be harsh.

3.) Lets hope not, cross that bridge when you come to it. I had one hole in my head where a bolt was used. The first few turns of the threads were stripped. I chased the hole with a tap. A stud screwed in past the damaged areas and had enough good threads behind to provide sufficient holding.

[divace73]

don't knnow about your model, but my 1980 has the heater extension pipe from the water pump to the rear of the engine that one of the heater hose connects to. This same pipe is connected to one of the studs and often has to be removed completely to remove the exhaust manifold. Coolant will leak everywhere as well.
Good idea to lower the level coolant below this point and have a spare gasket (I always make mine out of gasket paper) for the pipe to water pump.

[BenjamminsFiat]

Awesome! Once again, you've come through, thanks.

Is the purpose of cleaning the oil from the threads just so that the sealant can cure? Maybe some brake cleaner sprayed on a small diameter Barrel Brush would work...

There's enough oil all around that area right now, lol. I'm not going to worry if a little more comes out when removing the stud : ) I've got lots of Valve cover gaskets, would it make any difference to take the exhaust side off and add some oil there so it flows down into the Cam Tower? I have NO idea how the oil passageways work, but just thought I'd ask.