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MTU 12V 2000 M94 Cylinder Head Gasket Failure

Discussion in 'Engines' started by T.K., Dec 7, 2020.

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  1. T.K.

    T.K. Senior Member

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    Gentlemen ... Good morning and I wish you all a healthy and prosperous 2021.

    The MTU engine has now been reassembled, tested and is running normally. Only the cylinder head gaskets have been replaced. MTU have confirmed that the original cylinder head bolts were in good order and had not reached the max. shaft length of 212mm therefore, there was no requirement to replace them. The cause of the failure remains ambiguous. MTU assert that these cylinder head torque angle bolts cannot and should not be re-torqued. MTU have not commented yet about the material quality of the original cylinder head gaskets and whether any anomalies were found which could explain the failure. I need to chase them now that the year end holidays are over. I will keep you posted should I receive any additional information.
    Last edited: Jan 9, 2021
  2. Capt J

    Capt J Senior Member

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    MTU stated that the cylinder head bolts had not reached max shaft length and there was no requirement to replace them. MTU asserts that these cylinder head torque angle bolts cannot and should not be re-torqued?

    WHY would they re-use the cylinder head bolts after a catastrophic failure such as this??? I would'nt have even considered re-using the head bolts after this failure.
  3. GPO

    GPO Member

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    I agree with Capt J. Given the scope of work involved my preference would be, out an abundance of caution, to use all new replacement parts, especially when there’s some uncertainty regarding the specific cause. Once the engine is opened up use the opportunity to address all the potential variables.

    This has been an interesting post, thank you for sharing. I’ve been following it because of my own experience with one of my Cummins. Fortunately I was under warranty and Cummins was terrific. All new replacement parts.

    I hope that your issue has been successfully resolved.
  4. Donzi 54

    Donzi 54 Member

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    We would never reuse stretch bolts over again on cylinder heads. Maybe they are non stretch head bolts
  5. NYCAP123

    NYCAP123 Senior Member

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    If I read the posts correctly the heads have not been removed and the bolts are one-time-use. If they weren't damaged I understand not replacing them. 'If it ain't broke don't fix it'. Glad it turned out to be nothing more than a gasket replacement. It's what I expected and hoped for with the original post. As I said at the time motors overheat all the time from many causes. It doesn't make the motor toast unless ignored. I suspect your yard will be giving you VIP treatment from now on to help wash some of the egg off their faces.
  6. Capt Ralph

    Capt Ralph Senior Member

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    I remember talking with a JD tech. On the larger JDs, new stretch bolts every time.
    They are not torqued down, degrees of turns are measured in the final head bolt tightening regiment.
    I have never done this or witness this myself so I'm sure there is more to this, but he did state; new head bolts every time.
    This tech did mention, there is a special long taper on these bolts also.

    So, now I'm confused, MTU says do not re-torque the bolts, I read that as stretch bolts.
    MTU re-used the same head bolts, I read that a regular head bolts.

    Next question, are these bolts or studs/nuts?
  7. mapism

    mapism Senior Member

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    +1.
    That's precisely what popped to my mind while reading the last TK post.
  8. d_meister

    d_meister Senior Member

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    Angle torque, as specified by MTU brings the tension on a bolt to a specified level by first torquing to a known value and then turning the bolt a specific number of degrees. That achieves some bolt elongation and maximum calculated clamping force on the components. That is why they cannot be re-torqued, as you cannot go back to that initial torque stage and repeat it. If a bolt is turned loose to repeat the torque stage and then the angle torque finish, it may cause loss of clamping force and leaks, as well as achieving a stage of bolt elongation that can result in material failure.
    Since there is some elongation, there is a re-use specification provided. The amount of elongation specification can prevent bolt failure while assembling, which can result in wasted parts and labor. I first encountered this process in 1973 when I was trained on the PRV (Peugot, Volvo, Renault) Volvo B27 engines. It's common, now, but still attempts to deal with the immeasurable, which is how much clamping force is actually achieved?
    HERE is a very good explanation of what torquing bolts attempts to achieve.
    The process of torque-to-yield as a specified process results in fasteners that cannot be re-used.
  9. T.K.

    T.K. Senior Member

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    The MTU cylinder head fasteners are bolts.
  10. Capt Ralph

    Capt Ralph Senior Member

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    Darn good post.
    Thank you.

    Now I wonder, Was that head messed with before T.K. got the boat?
  11. T.K.

    T.K. Senior Member

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    MTU specify that MTU 2000 engine cylinder head bolts should have a maximum shaft length of 212mm. As long as the bolt shaft length is below 212mm the cylinder head bolts can be reused.

    I personally would have preferred using new cylinder head bolts however MTU confirmed that the original bolts were in perfect order and there was absolutely no reason to replace them. It wasn't only the decision of the local MTU dealer, the Aftersales Department and Product Support at MTU in Germany and the UAE were also involved in the incident and the decisions.

    The engine has been well repaired, however the failure remains frustrating due to the ambiguity of the cause of the failure.
  12. T.K.

    T.K. Senior Member

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    +1 Excellent post Meister ... you certainly know your business. I understand why you call yourself Meister.

    @ Captain Ralph ... I purchased the yacht new from the shipyard. Everything is possible, but it is highly unlikely that the cylinder heads were removed after the engines were installed into the yacht.
  13. Capt Ralph

    Capt Ralph Senior Member

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    Well then, This leaves near only one last failure explanation;
    Ship Happens..

    !cid_D67BCD71C9AA4BD0B39DAFAB273D895D@DESKTOPA25L25J.jpg
  14. ChiTown

    ChiTown Member

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    Logically ,It seems if these are torque to yield bolts and they are still within specified length, they were never likely torqued to yield (i.e. not fully / properly torqued down to begin with)
  15. gr8trn

    gr8trn Senior Member

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    Thanks to this thread I know more about bolt torquing and specifications for this application.
    Very cool.
    However, other than expenses, why not torque new bolts in light of the original idiopathic failure?
    Other than expense.
    Are we afraid the new boots are flawed?
    Interesting.
  16. ChiTown

    ChiTown Member

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    Total agreement, something doesn't make sense.
  17. d_meister

    d_meister Senior Member

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    With 800 hours, times 60 minutes per, times any arbitrary engine speed, let's say 1200 rpm= 57,600,000 revolutions, then divide by 2 (4 strokes = 2 revolutions) give us 28,800,000 detonations under each cylinder head. It's not looking probable that three cylinders began to leak oil due to incorrect assembly. Chances are slim that the engine would have made it off the test stand if they missed a step in assembly.
    I hope the problem is solved and it's as simple as defective head gasket material. Call me stubborn, but I'll stay with my original WAG (Wild A**ed Guess) about sudden rise in oil pressure from a relief valve-type of issue. I don't actually know if they have a relief valve, though. Must have, no?
    4stroke.jpg
  18. Capt Ralph

    Capt Ralph Senior Member

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    In these forums; That's SWAG:
    Scientific Wild Asp Guess... :rolleyes::rolleyes:
  19. Capt Ralph

    Capt Ralph Senior Member

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    I'm sure they do have oil relief valves. That is not going to blow a head gasket on it's worst day though.
    Steam or pressurized water will.
    I think I commented that in post #51 and nobody bit into it.
  20. d_meister

    d_meister Senior Member

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    Without re-reading the whole thread; if I remember correctly it is only an external oil leak, and no breach from coolant to oil or vice-versa. Also no coolant external leak. Oh, well, if trained technicians and the big guns at MTU haven't figured it out, chances aren't good for me doing it from here.

    Ralph, thanks for the SWAT enhancement. My mother always said a good vocabulary is important, and you've improved mine, today!