Exhaust manifold leak

Engines, Exhaust and Fuel Systems

  1. 88_AHB

    88_AHB Well-Known Member

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    Hey everyone,
    Have a different situation with my newly acquired exhaust manifolds on my 318. So I switched over from headers to manifolds. Installed a set of M body manifolds w/AIR,both ends on the manifolds have been capped off for emissions etc.

    Now I take it down to the exhaust shop after they bend up pipes to make up the difference between the headers to manifolds. Go to fire it up and the exhaust guy says you have leaks from the bottom on the AIR holes where it meets up to the head. When the motor was rebuilt,the holes for the AIR were plugged in the head. Now I did not put a set of gaskets on when switching,never had to use a set on cast manifolds and heads YET.

    I was hoping if I simply install a set of good exhaust gaskets,would this resolved this issue? I really was hoping I don't have to find a set of of manifolds without/AIR. Unfortunately I have the feeling that I might have to find a set to correct this issue,I swear I have the worst luck lol. Any help with be much appreciated before I spend more time,money and frustration.Thanks
     
  2. Aspen500

    Aspen500 Well-Known Member

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    If you can't find gaskets for the AIR block off plates, Permatex Ultra Copper RTV will work good. If needed, a light bead can also be put around the manifold to head mating surfaces. Let it cure a day or two before starting the engine and 99% of the time, the seal is permanent. On the old headers I had on my Aspen back in the early '90's, I tried every kind of gasket made and within a few days,,,,,,leaks. Put a bead of Ultra Copper around each port with no gaskets, let it cure a week and they never leaked again. In fact, I had a heck of a time getting them back off a couple years later. Seemed like they were welded to the heads. lol.
     
  3. volare 77

    volare 77 Well-Known Member

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    I don`t think you will find a gasket that will cover those hoses. Remflex gaskets seal well if they cover that area but i doubt it. If they were plugged correctly they shouldn`t leak. If the plugs come out then I would try and put some red high heat silicone on the plugs and reinstall them. Are the plugs flush or recessed in the holes? Many use just the red hi temp sealer on headers instead of gaskets because they have a problem with them sealing so maybe that will work for you. Maybe you have a warped manifold causing it to leak??? Check it with a straight edge.
     
    Last edited: May 30, 2020
  4. Aspen500

    Aspen500 Well-Known Member

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    I just reread your post and discovered I misread it before as to where they were leaking. For some reason I thought you meant the block offs of the rear of the manifolds. At any rate, the Ultra-Copper RTV should do the job. As Volare said though, make sure the manifolds are flat and check the heads just to be sure as well. Manifolds can be "planed" easily at a machine shop on a wide belt sander. Takes about 5 minutes and doesn't cost much.
     
  5. 88_AHB

    88_AHB Well-Known Member

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    Thanks guys,
    The plugs that are in the head are flush and are still in there. They never leaked when I ran headers. I was hoping that a gasket or either the red or copper RTV would resolve the issue without having to find Non AIR manifolds. I will pull the manifolds off again and check to make sure they're flat. Would there be any reason to run a gasket instead of using RTV other than sealing issues? or the other way around?
     
  6. Aspen500

    Aspen500 Well-Known Member

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    A gasket may do the trick but a lot of times actually makes the leak worse. In my experience (for what it's worth) putting manifold gaskets on where none were used originally tend to not last, especially if it's the perforated metal looking ones. If the manifolds have leaked long enough, you will be able to see evidence of where the leak is by the black soot trace.
     
  7. Mikes5thAve

    Mikes5thAve Well-Known Member

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    My manifolds never leaked until I had the heat riser replaced in one and someone put it back on with a gasket.
     
  8. brotherGood

    brotherGood Well-Known Member

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    I've been thinking about this since you told me and I'm still lost.

    The manifolds never leaked when I had them-and I even had a bolt backed out for a few months..they still sealed well.

    Stupid question, but could the O2 be the source of the leak? I pulled the old one out to ship, but threw the new one in the box. I'd think thatd be a bit more obvious, but I'm really grasping at straws
     
  9. 88_AHB

    88_AHB Well-Known Member

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    No they’re not by the o2. It’s at the bottoms of the air ports where they meet with the head.
     
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  10. XfbodyX

    XfbodyX Well-Known Member

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    Now I take it down to the exhaust shop after they bend up pipes to make up the difference between the headers to manifolds. Go to fire it up and the exhaust guy says you have leaks from the bottom on the AIR holes where it meets up to the head. When the motor was rebuilt,the holes for the AIR were plugged in the head. Now I did not put a set of gaskets on when switching,never had to use a set on cast manifolds and heads YET.



    Think about it, you air holes in your head are plugged and keeps ex from going out of them. If they were not there the ex would go through the manifold and down the ex pipe sooner or later.

    Now you have a manifold full of ex pressure and 4 tiny holes butted against wall and some leak and some dont and yours do.

    Could you of used a bigger then normal plug in the head when you drilled and tapped?

    Whatever the case when ive had this happen on a mopar or any brand, simply lightly bevel the holes in the manifold and hit them with nickle rod or braze shut and die grind just below flush, no air coming from air holes.

    If your really trying to tell where the leaks are like Aspen79 said there can be a trail, but you can speed it up by manually manipulating the choke on your car and get it to lope and smoke rich like a diesel then yank them.

    Lastly, the whole plug the heads was a trick that was for to run headers on smog heads and works great, always mixed results trying to trick oem parts into doing something they were not meant to do.
     
  11. Demonracer

    Demonracer Member

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    How did you block off the holes? On my late model heads, I drilled & tapped them to use allen screws in them with high temperature Loctite. I'm running headers & have ho problems with leak.
     
  12. XfbodyX

    XfbodyX Well-Known Member

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    Read it all, he did the mod and ran headers with no issue, now hes going back to air manifolds and the manifolds are leaking around the air hole areas.

    Unless im reading it wrong, which is very very possible with me.
     
  13. LSM360

    LSM360 Well-Known Member

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    I agree, using gaskets with manifolds may create more problems than it solves. Remflex are good gaskets if you do choose to use, as previously written.

    It really sounds like your best solution is to go back to running a good set of headers with Remflex gaskets, but I guess it's probably to late now that you have spent money on head pipes.
     
  14. Mikes5thAve

    Mikes5thAve Well-Known Member

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    I'm thinking this is more of a problem with the exhaust manifold leaking somewhere because it would be some quincidence if those plugs suddenly decided to leak now when they didn't with headers.
    They are also covered by the exhaust manifold so even if they did leak they should be blocked by the manifold. Leakage shouldn't be a problem unless the manifold surface isn't flat anymore or those plugs are protruding a bit causing it to not seal right.
     
  15. 88_AHB

    88_AHB Well-Known Member

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    Originally when the heads were rebuilt, I was just going to run headers and didn't think twice. Now things have change and prefer to go back to manifolds. Never had these plugs leak before and not leaking now. I never (officially) checked the manifolds to make sure they were straight,they looked it and seemed fine by appearance. I honestly don't know what sort of plug or whatever the machinists put in the heads. Last time I looked at them they did seem to look/feel flush. I also considered looking for a set of NON air manifolds to bypass all these issues.
     
  16. Mikes5thAve

    Mikes5thAve Well-Known Member

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    Do what someone mentioned before and get a machine shop to "plane" or true the exhaust manifolds To ensure that you're at least starting with a flat surface. If you're worried about the holes in the manifold causing a leak after that get the machine shop to plug them at the same time.
     
  17. BudW

    BudW Moderator Staff Member

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    Be sure to scrape off any paint, while manifolds are off. Paint buildup (or paint burn off) has caused problems for me. Not saying this an issue for you - but might be. Chrysler exhaust manifolds (except for /6) do not give much problems (as brand X and Y does).
    Note: when new, Chrysler painted the engines after exhaust manifolds were installed - which I thought was odd because the paint always burnt off. BUT - you can always see where the manifold fit on the head. When another manifold is installed - sometimes, due to casting differences, the new manifold will rest on top of old paint, which results in a leak. A couple scrapes with a gasket scraper will resolve that (except for the extra manifold removal/reinstall time).

    If A.I.R. ports were tapped and had pipe plugs inserted (which have a bit of a "V" shape to them) then I don't see that being a problem. Been my experience the port holes fill up with carbon deposits in no time which eliminate that problem entirely.
    BudW
     
  18. 88_AHB

    88_AHB Well-Known Member

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    Not the best pic, I brazed up the holes. I haven't done any brazing in over 10 years so excuse the mess lol. After this I took the manifold to get resurfaced,holes still looked to be filled thereafter. Mounted the manifold,ran a bead of red RTV on the surface let it cure overnight. So far have driven around a few hours over the past couple days so far no leaks to speak of. I had a few rods of silicon bronze and brass.The first hole I used the silicon bronze,for me it didn't like to work that well. Tried brass on the other holes and had better success so stuck with that.

    thumbnail_IMG_0394.jpg
     
  19. Aspen500

    Aspen500 Well-Known Member

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    Good deal! :cool: Few things are as annoying as a manifold or header leak at the flange. Make's it sound like an F150 or Dodge/RAM with a Hemi or 4.7L. TICK, TICK, TICK, TICK from the broken manifold mounting studs in the heads.
     
  20. 88_AHB

    88_AHB Well-Known Member

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    I never tried to braze anything with cast iron. I used the rods with the flux already on them. Heated up the manifold a bit (not too much) and it seemed to stick. Just keep building it up and going around letting it briefly cool and keep doing this process seemed to work.