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Thread: Cracked exhaust manifold

  1. #1
    DaddyMack
    I have a cracked Exhaust manifold in a 1980 350 chevy (mercury 260).
    It is the old style with the exhaust at the end of the manifold (rather than center rise). I was thinking of taking it off and grinding it and then welding. Is it worth it? Will the new style work also? a new manifold is a min. of 200 bucks for one side.
    the leak is rather minor. it wont sink the boat and it won let the manifold run hot, in fact it mostly steams away, but there is rust... etc..
    ideas or suggestions?
    thanks!

  2. #2
    Ryan00TJ
    Same engine that came in my Hammond new Merc 260. I've heard that a good welder can weld cast iron. There's not too much pressure at that point so a option would be to grind the rust away, clean with strong solvent, add JB weld or Allmetal. Now as to the thermal expansion and how it will handle it that's not a given. Might leak again and might not.
    The new style center riser will work but all associated hardware will be required also.

  3. #3
    Senior Member
    Join Date
    Feb 2009
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    678
    i have used both JB weld & liquid steel with good results on a chevy straight 6 & a ford 4 cyl...no thermal expansion...just make sure, as stated, to clean the area good!
    fastrat

  4. #4
    DUCKY
    A competent welder can weld cast iron. The key is the heat up the surrounding area with a torch, weld it and then let it cool slowly. Please don't use epoxy or the like. The big question is if it's cracked on the inside as well. You should remove it, and have it leak checked. If it will let water into your motor, the $200 manifold is the least of your worries. If it cracked due to a freeze, you probably should replace it.
    PS, do you still have the little jet boat? If so, where are you located. I'd like to have a look at it.....

  5. #5
    DaddyMack
    Ducky...
    I don't have a jet boat... not for 20 something years... but I have the boat I am bringing to you on Sat afternoon or Sunday mornng this coming weekend... ))
    THanks for all the replies!! I am thinking of just spending the 200 bucks.... I never thought of the fact that it could be cracked all the way through the exahust side...
    The only reason I thought of changing to the center rise was performance.... but then again.. they are cheaper for some reason as well. I may take a look at a newer set up to see what I can do. Would I have to go through the hull? hmmm third thought..lol.. If I do the 396 change out later in the year I will prob want the center rise anyway.
    THinking that changing over to the center rise might be the best bet. I would guess they are a little more efficient also since they are newer?

  6. #6
    Senior Member
    Join Date
    Feb 2009
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    678
    just food for thought!, but, IMO if ur gonna do a 396 chng out later in the year! (i'm presumming this is a BBC?) why not just JB weld or use liquid steel for the leak & save the money for ur new set-up??...i think u would be way ahead of the game!...just my .02 cents
    fastrat

  7. #7
    DUCKY
    Ducky...
    I don't have a jet boat... not for 20 something years... but I have the boat I am bringing to you on Sat afternoon or Sunday mornng this coming weekend... ))
    THanks for all the replies!! I am thinking of just spending the 200 bucks.... I never thought of the fact that it could be cracked all the way through the exahust side...
    The only reason I thought of changing to the center rise was performance.... but then again.. they are cheaper for some reason as well. I may take a look at a newer set up to see what I can do. Would I have to go through the hull? hmmm third thought..lol.. If I do the 396 change out later in the year I will prob want the center rise anyway.
    THinking that changing over to the center rise might be the best bet. I would guess they are a little more efficient also since they are newer?
    I guess I got you confused with someone else..OOPS!!!
    Anyways, the center rise manifolds are certainly better for making power (with other changes), and they are cheaper because there are at least 10 different companies making them. They are also lighter. PS..Why are you thinking of putting a big block in it? And in front of an Alpha? I wouldn't.... I'd put a little money in a 383 or 406ci small block, that will bolt right in. Just my opinion...

  8. #8
    Jim W
    I have never had any luck with the epoxy/JB weld stuff. The manifold or engine block gets just a little bit too hot and the plastic goes soft.
    What works really well is to braze the crack or cracks up. simple to do and works well. It's really hard to find someone to weld cast iron and have it work. Almost anyone handy with a torch can braze...
    Be good, Jim

  9. #9
    DaddyMack
    Scott.. 396 is small block... at least the one I am probably getting... and I think the 350 exhausts bolts right up...
    425 hp and 415 ft·lbs torque... stock - roughly..one of my favorite GM motors..
    Brazing might just be the way to go excellent and inexpensive solution! what kind of metal do you think? bronze? and what temp... wonder if it will work with home torch...

  10. #10
    GUGS102
    We had a sea ray with the same problem on the manifold. We brazed it and it held. I've got a set of straight elbows if you want to go through the hull with the exhaust.
    I bought them to make the conversion on mine but sold the boat before I got around to it.
    http://www.***boat.com/image_center/...100166-med.JPG

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