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  1. #1
    Light Load Member metric adjustable's Avatar
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    M11 exhaust manifold bolts

    I own a '99 Freightliner with an M11 cummins under the hood. So far the engine as been good to me, but has a couple of annoying problems. The worst one (to me) is the #6 cylinder lower exhaust manifold bolt. The ###### thing cannnot seem to last longer than a year, and keeps snapping off flush with the cylinder head. Lots of time to drill out, since it is partially under the cab.

    In the years i've owned the truck, it has gone through six #6 lower manifold bolts, and one upper on same cylinder. Nothing is contacting the cab, the cylinder head is not original, the exhaust manifold is the only original thing in that area.

    Any ideas why this particular bolt keeps snapping off? Is it just perverse chance that the only one breaking regularly is the hardest one to get at?
    Am I the only one with this minor yet annoying problem?


  2. #2
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    I would take a look to see if the exhaust manifold or head is a true flat surface. Other than that I don't know.

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  4. #3
    Road Train Member bender's Avatar
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    I agree, exhaust manifolds will distort when engine has been operated with broken or missing mounting bolts/studs. Also, the manifold must be allowed some movement on the mounting when expanding and contracting during temp change. Over torquing the mounting bolts can hinder movement and pop the bolts. The mounting bolts can also be sheared off by too little clearance to the hole edge on the mounting flange. Drilling the mounting flange holes oversize in the manifold flange will allow proper movement without shearing the bolts/studs.

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  6. #4
    Road Train Member AUSSIE DAVE's Avatar
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    My guess also would be over torque of the bolt . On my m11 the manifold will expand and move about 1/8inch.

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    Road Train Member Heavyd's Avatar
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    If you have to drill out broken bolts, they weren't installed properly. Any pro will apply anti-seize to exhaust manifold bolts. That won't prevent them from breaking, but you'll never have to drill them out. They break because they are getting sheered from the exhaust manifold expanding. The manifold is suppose to have some flex at the joints between sections. If those joints do not absorb the expansion then the bolts take the stress. You may need to replace the exhaust manifold too.

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  10. #6
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    I take it you have a 112 and many times the drain for the cold air box. Air intake flactuator valve, will drain onto the exhaust manifold.
    When you remove the bolt, you want to tap out the threads then, I have a mixture of never size, ATF, and synthetic gear oil put a bit in the bolt hole then coat the threads.
    Manifold can be resurfaced on a belt sander, Both the head side surface, and the turbo mount surface, the expansion joints can not be, I have seen many people try none succeed.

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  12. #7
    Light Load Member metric adjustable's Avatar
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    thanks to all... never considered drilling the offending bolt hole(s) oversize, might be worth a try before going for a new manifold. That or Grade 200 bolts, if i can find 'em.

  13. #8
    Road Train Member AUSSIE DAVE's Avatar
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    Quote Originally Posted by metric adjustable View Post
    thanks to all... never considered drilling the offending bolt hole(s) oversize, might be worth a try before going for a new manifold. That or Grade 200 bolts, if i can find 'em.
    I would NOT change the grade of the bolts, just reface manifold install new gaskets, use anti seize on bolts, and torque to spec.

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  15. #9
    Heavy Load Member SmokinCAT's Avatar
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    Also, if it is a 3 piece manifold, when you have it off hammer the ends towards the center, hopefully the back section will move enough that it will keep pressure off of the bolts when it expands.

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  17. #10
    Light Load Member metric adjustable's Avatar
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    It is a three piece manifold; always thought the mating areas would allow expansion/contraction to avoid snapping bolts or warping manifold.

    If i do decide to try pulling off my own manifold, is there anything i should do beforehand to make it less likely to snap off remaining bolts? Would it be better to remove remaining bolts when engine is warm or cold?

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