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Thread: broken exhaust lobe, any suggestions

  1. #1
    Join Date
    Sep 2009
    Posts
    3

    Default broken exhaust lobe, any suggestions

    Hello all!

    Well this evening I was removing the exhaust manifolds from my 304 and while doing so I managed to break off the center lobe on the head that the bolt for the exhaust manifold threads into. So now I have a half manifold bolt hole. And since there are only 5 bolts that hold the exhaust manifolds on, I would think I need every bolt hole. My only idea was to braze a stud into what is left of the hole. However, would this be strong enough? And with all the oil and grease in that area, I'm not sure I could get it to stick. I have read that I could weld steel to cast using a nickel alloy wire, but I would hate to spend the money for an entire roll only to use a few inches and probably different shielding gas. I am guessing its expensive...just guessing though. Everything I've been taught is that you can't weld steel to cast using conventional mild steel wire.

    Any other suggestions on what I could do???

  2. #2
    Join Date
    Jun 2009
    Location
    Hurlburt Field, FL
    Posts
    495

    Default

    You can weld cast iron with normal welding wire if you've got a good torch to heat up the cast. Get it red-hot (without getting too hot, too close to melting) and then hit it with the welder.

  3. #3
    Join Date
    Feb 2009
    Location
    Aiken, SC
    Posts
    2,423

    Default

    Last time I did that, I welded a stud in place. Still used the broken piece. Center hold is the short one, IIRC, Smallest stud you can find with the correct thread.

    At the time, it gave me the idea of fabricating up a support bracket that would go between the bolts in case that ever happened while changing exhaust manifold gaskets. Never followed up with it. One thing I did start doing was use my torque wrench and anti-seize, and always make sure those particular bolts are in good condition. The heat eventually has a detrimental effect on them. As you now know, the cast iron breaks before the grade 8 bolt.

    The reason the keeper washers are on there is because the bolts will work themselves loose with regular lock washers. This is from the expansion/contraction rate variation. I often replace the intake manifold gaskets when I replace the donuts unless the gaskets are fairly fresh, as in less than a year old. I do this because I use far fewer words that I would not want anybody to hear me say at church. It's just a whole lot easier to set it all up properly.
    Allan E.
    Curmudgeon Extraordinaire
    Charter Member, Old Hippie IH Club
    Old fashioned binder freak

  4. #4
    Join Date
    Sep 2009
    Posts
    3

    Default

    Thanks guys. That was what I wanted to hear.

    I hoped to be able to weld a stud right into the bottom half (the half still attached to the head) of that lobe. I'm glad other people have successfully accomplished this as well. So this is really good news for me.

    I know the differential cooling rates of the two different metals, i.e. cast iron and steel, is why the welds typically fail. Hopefully mine won't. A union welder also advised me to keep mild heat on it for a while and cool very slowly.

    I guess I should blow the dust off my torque wrench.

    Thanks again.

  5. #5
    Join Date
    May 2009
    Location
    AZ
    Posts
    21

    Default

    A lot of times the stud will just turn right out because it breaks inside where the manifold is leaving threads exposed sticking out the head when you pull the hole manifold. try turning it out first if no go than weld a nut on the stud and use lots of penny oil.

  6. #6
    Join Date
    Mar 2009
    Location
    California
    Posts
    110

    Default

    When welding cast iron with steel, be it wire or stick, the transition area ends up being very high, to high carbon steel. This needs to cool slowly to prevent hardening and even so, different expansion rates for it, the outer attached piece, and the cast iron will cause some residual stresses. The high preheating necessary to do a good job also can warp the head, if not done properly.
    Nickel adsorbs carbon when molten but releases it as it cools, giving an expansion rate similar to the cast iron; it is also more malleable and doesn't heat treat, that is, is not hardened by quicker cooling. Thus, the degree of preheat is considerably lower to get good results.
    Nickel stick electrodes may be available in small quantities at your LWS, (and some friend may have a stick machine to use?) or it may be safer and cheaper in the long run to have a welding shop do the work for you.
    If you are interested in seeing a few examples of Cast Iron repairs, see these:

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