Cracked Manifold
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HT4100 4.1, 4.5, 4.9 Discussion, Cracked Manifold in Cadillac Engine Technical Discussion; Sup guys ... I have a problem with my Deville 94. My manifold have a little "scratch" and I need ...
  1. #1
    Dieslow is offline Cadillac Owners Member
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    Cracked Manifold

    Sup guys ... I have a problem with my Deville 94. My manifold have a little "scratch" and I need to replace it. I'd like to know if it is possible to fix it instead 'cause it's pretty expansive (800$can + install) ! IS it possible to do some sort of "welding" on it ?

    Thanks for your answers you guys are awesome !

    Peace !!

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    DaveSmed's Avatar
    DaveSmed is offline Cadillac Owners Connoisseur
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    Re: Cracked Manifold

    How little is little? Got any pics you could post of the manifold in question?

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    Dieslow is offline Cadillac Owners Member
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    Re: Cracked Manifold

    Sorry ! I didn't even think about posting a picture ... i'll poste 2 and if you want more just tell me !

    Thanks a lot !
    Attached Images

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    Re: Cracked Manifold

    Any decent welding shop should be able to do it

    I have fixed quite a few in worse shape than yours.

    1. The manifold should be glass or sand blasted clean.

    2. Drill 1/8" holes at the ends of the cracks (this is called "stop drilling") to prevent the crack from lengthening when being welded.

    3. Use a porting or similar tool, to grind a groove along the crack(s).

    4. Preheat manifold in an oven at 450 degrees for about 30 minutes.

    5. Remove to welding area and arc weld with NI rod. Weld about an inch, then change locations and weld another inch. This helps avoid overheating.

    6. When finished bury in clean sand and allow to cool for several hours.

    7. Have the manifold mounting surface blanch ground to provide a flat true surface.

    -George

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    Dieslow is offline Cadillac Owners Member
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    Re: Cracked Manifold

    Would this be less expansive than buying a new one ?! IT seems pretty long and hard job to do ...

    Thanks again !!

    Peace !

  7. #6
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    Re: Cracked Manifold

    While the welding process sounds a little complicated, it is a very straight foreword procedure for a professional welder, not the guy at a corner muffler shop. Seek out a professional welder or a business that does machine repairs.

    I would expect to pay about $75-$100 for the welding and $20 for the flange grinding. Much less than the $800 you mentioned for a replacement manifold.

    Perhaps a better alternative would be getting one from a wrecking yard, if one is available.

    -George

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    Dieslow is offline Cadillac Owners Member
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    Re: Cracked Manifold

    Last thing I need to know ... does a cracked manifold influence on the fuel economy or not ?! Thanks again !

  9. #8
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    Re: Cracked Manifold

    Quote Originally Posted by Dieslow
    Last thing I need to know ... does a cracked manifold influence on the fuel economy or not ?! Thanks again !
    It could. The exhaust system has both positive and negative pressure pulses traveling inside. The negative pulses can (and will) pull air into the exhaust system which will throw off the O2 sensors. If the O2 sensors see the air being pulled in then it will cause the sytem to richen up to compensate which could adversely affect the fuel economy.

    The real concern with a cracked manifold is the possiblity of CO intrusion into the passenger compartment. With exhaust leaking into the engine compartment it can be picked up at the cowl vent and sucked into the HVAC system. CO poisoning is a real threat and a real reason to have the manifold crack repaired.

  10. #9
    Dieslow is offline Cadillac Owners Member
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    Re: Cracked Manifold

    Quote Originally Posted by bbob
    It could. The exhaust system has both positive and negative pressure pulses traveling inside. The negative pulses can (and will) pull air into the exhaust system which will throw off the O2 sensors. If the O2 sensors see the air being pulled in then it will cause the sytem to richen up to compensate which could adversely affect the fuel economy.

    The real concern with a cracked manifold is the possiblity of CO intrusion into the passenger compartment. With exhaust leaking into the engine compartment it can be picked up at the cowl vent and sucked into the HVAC system. CO poisoning is a real threat and a real reason to have the manifold crack repaired.

    Alright !! I'll have it fix Monday !
    Thanks a lot for your precious help !

    Peace !

  11. #10
    El Dobro's Avatar
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    Re: Cracked Manifold

    Go to www.car-part.com and do a search. When I had a 4.9, I would just order the manifolds from one of the listings for about $25-30 each. No welding, no fuss, no muss.
    You may also want to check the rear manifold too. They're usually no too far behind the front one on cracking.

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