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Mtu 396 TE piston problems

Discussion in 'Engines' started by dave7, Dec 15, 2008.

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  1. dave7

    dave7 New Member

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    Hi , anyone have any idea on this one, i have had a on going problem with my port main engine , i kept looseing my valve gaps , after re gapping twice in 50 hrs i put the camara down the head to find all my seats were finnished (hammerd) i have had all the heads rebuilt and 2 new pistons and liners in b1 and b6 they showed sighns of wear. (this is ok) during the sea trial piston b4 picked up and pulled the crown off. unit is finnished, when i put the camara back down i have nearly all my liners and pistons damaged. All parameters was in set values layed down by MTU, no alarms etc but lots of damage, ( injectors are fine) (Not a air lock as it was one hour into sea trial)

    Thanks for any ideas.
  2. Marmot

    Marmot Senior Member

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    What is the condition of the turbos? Almost imperceptible loss of turbo efficiency can lead to overheating of exhaust valves and the kind of damage you described. Once you have some tramp metal flying around you are almost guaranteed to have more turbo damage as well.
  3. dave7

    dave7 New Member

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    I had the turbos and intercoolers seviced last year , i have checked the turbos and all is ok on visual inspection. i seam to have a heat problem as the piston crown picked up in the liner and other pistons are now showing damage to crown and liners after the sea trial, before the trial all liners were inspected and ok apart from b1 and b6 which were replaced , what i know is the engine is back to max horse power having all the heads rebuilt ,. maybe generating more heat than before , i had plenty of oil pressure too 5.5 bar , what about a oil cooler prblem?
  4. K1W1

    K1W1 Senior Member

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    Hi,

    Have you had the Camera in your Stbd Engine?

    Excessive Exhaust Backpressure caused by a restricted silencer etc can also have a pretty heavy effect on Exhaust Valves, you would normally see this in your EGT though.

    I was on a boat with a pair of 16V 396 TB94's that were rated at 3520 HP.

    We used to regularly see 800 Deg C in the Exhaust- we also had a number of B1 Turbo Charger failures.
  5. dave7

    dave7 New Member

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    Hi,

    yes i had the camara down stbd engine when i did the turbos and intercoolers last year just for check and all was ok , it just seams to be the port engine, my alarm on the bulk exhaust is set at 800 deg c , and when the crown picked up the temp was 725 deg c , i do know at 1600rpm parameters are near limits (fuel rack/exhaust back pressure etc) but within, because as this is where the yacht is about to come up onto plain and after this i can expect load to be less on the engine. also when i was looseing my valve clearance it was intake and exhast.

    Cheers.
  6. Marmot

    Marmot Senior Member

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    I neglected to mention that a slight overload in combination with poor scavenging will combine to create the problems mentioned. have a good look at the prop or pump on that side.
  7. dave7

    dave7 New Member

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    Ok thanks for you help, will let you know how i get on.
    which pump do you mean ? fuel pump?
  8. Marmot

    Marmot Senior Member

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    By pump I meant the impeller if you are running a jet drive. It doesn't take much of a tweek to increase the loading of either. Ask K1W1 about his recent experience with that one ...

    If the boat seems to be hanging up at the point where the power demand should drop off as it gets on plane it is staying in a high drag condition and that is where you are likely to sustain a slight overload and incur heat damage. I had that problem with a 396 powered jet boat There were nearly identical symptoms attributable to a middle aged weight gain ... the boat, not me.
  9. dave7

    dave7 New Member

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    Also if anyone knows if its normal to see on the piston crowns where the fuel is being injected eg shine spots on the crown?
  10. dave7

    dave7 New Member

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    rrrr ok thanks for that, am running shafts on this one with ZF G/B


    Cheers.
  11. Marmot

    Marmot Senior Member

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    "... shine spots on the crown?"

    Localized high temperature burns off the carbon. This is consistent with overloading. I would check the accuracy of your EGT display.
  12. K1W1

    K1W1 Senior Member

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    Hi,

    The loss of Valve Clearance is either the valves settling further into their seats and the heads or the heads about to pull off and stretching the valve stem there by sticking further out of the guides.

    Shiny spots on your pistons in the area of Injection can indicate an increased viscosity of the injected medium and having it stick and burn on it's way across the Piston Crown.

    Is your fuel good?

    I know of another yacht with these engines that had similar problems and it was blamed on fuel quality by MTU.
  13. Marmot

    Marmot Senior Member

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    "... it was blamed on fuel quality by MTU ..."

    But this appears to effect only one engine.
  14. dave7

    dave7 New Member

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    yes this is just the port engine i am having trouble with, is there a chance that i have oil cooling problem , i know oil can be bypassed to the oil pan ,is it possible one of the bypass valves in the oil cooler has stuck or contaminated sending uncooled oil back to the spary nozzel. do think its worth haveing the oil cooler checked . i will also get a load test done during next sea trial.

    Cheers.
  15. dave7

    dave7 New Member

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    yes this is just the port engine i am having trouble with, is there a chance that i have oil cooling problem , i know oil can be bypassed to the oil pan ,is it possible one of the bypass valves in the oil cooler has stuck or contaminated sending uncooled oil back to the spary nozzel. do you think its worth haveing the oil cooler checked . i will also get a load test done during next sea trial.

    Cheers.
  16. K1W1

    K1W1 Senior Member

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    Hi,

    It affects one engine that he knows about, he said his last visual of the Stbd one was last year.

    If it sits a lot the fuel could have gone bad also gummed up rings ( another symptom of too little use and exhausts open to atmosphere)on these things cause massive oil burn around the edge of the piston crowns.
  17. Marmot

    Marmot Senior Member

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    "... he said his last visual of the Stbd one was last year."

    You've got a point there. But, if the stbd engine was suffering the same problems I would think it would have shown up by now.
  18. Capt J

    Capt J Senior Member

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    I too would check the fuel. On Many yachts one engine runs off of a different fuel tank then the other engine. I've seen where a marina in the NE (USA) was selling heating oil as diesel. I would have the fuel tested. Also check the vent for the fuel tank and make sure it is not clogged. If it's a load issue, I would think he'd be seeing problems with the stbd engine also, unless the tachometer is off and he's running the port engine 100rpm more then the stbd and dragging the stbd engine and running a much higher load factor on the port engine. It sounds like it may also be a fuel starvation issue of some kind. I would run fuel pressure gauges on both engines and verify proper fuel pressure. Water in the fuel will also do the things that are described. Clogged aftercoolers may also create a high intake or fuel charge temperature and create issues also.
  19. Marmot

    Marmot Senior Member

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    I really doubt it is fuel if it only effected one engine over an extended period. Besides, bad fuel usually manifests itself in other symptoms that are visible to those who are looking.

    A damaged or tweeked prop only effects the engine that drives it.

    What is fuel starvation going to do to the cylinder components of a diesel?

    "fuel charge temperature" ???
  20. dave7

    dave7 New Member

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    Hello ,

    Thanks for all the help on this one everyone, i have a meeting today to talk about this engine , I will have the fuel checked anyway thats easy to do. any veiws on fuel pump and oil cooler.? at the mo it sounds like a load problem.?? on one engine i think having the tacho tested is a good idea but the fuel racks seam to be in the same poistion when i am running. would this tell me that the engines are balanced.