Mercruiser D-tronic 2.8L 165HP inlet valve failure

Discussion in 'Diesel Engines' started by ruurd, Jul 9, 2013.

  1. ruurd
    Joined: May 2011
    Posts: 14
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    Location: Netherlands

    ruurd Junior Member

    Good day members,

    I want to share something and like your opinion on it. I own a Mecruiser 4 cyl diesel engine for 2 years now. When I bought the boat the engine had only 75 hrs on it, which is bad because it was stored in a wet boat.

    After running it for 24 hrs. the inlet valve suddenly cracked from the nr 1 cyl. I managed to sail back to port with a little luck after all so the valve dind't brake completely.

    Now the question is why the inlet valve suddenly cracked. My only explanation is that the valve stem was not at a right angle to the valve(seat). I know that an engine with so little running hours compared to it's age (1999??)is not very good for the engine but an braking valve like this should not happen.

    see pictures at;
    https://www.dropbox.com/sh/wqqakv8bwmoi34h/sXEZ-dXy5q
     

    Attached Files:

  2. baeckmo
    Joined: Jun 2009
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    Location: Sweden

    baeckmo Hydrodynamics

    That's due to a leaking intercooler (and btw its the no 4 cylinder..). Problem with this engine, if not stored or preserved ok, is that there has been early engines with leaking intercooler tube bundles, either caused by bad soldering or corrosion at the rear end of the bundle.

    The tubes are placed right on top of the inlet openings in the manifold (with no escape hole or similar), so any water from the cooler will drip right down into the inlet of the lowest cylinder, normally the no 4. You seem to have come out of it on the lucky side; I have seen worse damage on a similar unit.

    And that's a pity, because I like that engine and the way it is built and performing. I remember having tried to make forum members aware of this problem in another thread, but unfortunately, that is of no comfort to you right now.

    So, check that the piston is not damaged, and that it is not "sitting lower" than the others (might indicate a bent connecting rod), put new valves (BOTH!!!) into the head and take the intercooler complete to a cooler/heat exchanger specialist and have it pressure tested and fixed. If the engine has been stored in a damp environment, I would have the turbo bearings checked as well.

    Good luck!
     
  3. ruurd
    Joined: May 2011
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    Location: Netherlands

    ruurd Junior Member

    Off-topic; Great response! That's what I like about this forum. Motivated answers from professionals and experienced users. Great! Also Baeckmo gave me a lot of information about jet drives before.

    Now I remember you told me about this weak spot before I bought this boat, but because the engine had so little running hours I didn't think it would become a problem so soon.
    A little strange is that the valve broke after using the engine for 30 minutes at sea and not directly after starting. However it's probably no coincidence that the nr 4 cylinder broke down. After the breakdown the boat was on it's trailer with a drained seawater system during winter. Than last month I cranked the engine without the injectors installed to test the compression. Although the seawater system was drained I noticed a water spray coming only from the removed injector on nr 4 cyl. This supports your story about the leaking intercooler.
    I will try to pressure test it in the workshop myself first to hopefully discover the leakage.
    Maybe it's also possible the mount some kind of float system to drain any excessive water if it happens again in the future.

    On the turbo it seems to be okay for now. When the boat arrived 2 years ago the turbine blade were rusted stuck against its housing, indicating bad storage for a long time. I managed to free the blades with WD40...
     
  4. ruurd
    Joined: May 2011
    Posts: 14
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    Location: Netherlands

    ruurd Junior Member

    I managed to pressure test the intercooler. I filled it up with freshwater and pressurized it for 1 hour with 5 bar. "Unfortunately" I didn't find any drop of water coming from the cooler bundle.
    It's however suspicious that looking in to the nr 4 cyl it has more salt crystals and rust formation that the other 3 cyl. But I can't confirm that it's coming from the cooler.
    I checked the piston height and luckily it has the same height as the others.

    I agree it remains a weak spot of this engine, when looking at the intercooler bundles as they are positioned on top of the engine.

    Pictures @ https://www.dropbox.com/sh/wqqakv8bwmoi34h/sXEZ-dXy5q

    Another question, looking at the serial nr can you tell me what is the year of production??
     

    Attached Files:

  5. baeckmo
    Joined: Jun 2009
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    Location: Sweden

    baeckmo Hydrodynamics

    It may well be the sealing between tube bundle and housing that is causing problems, due to the difference in thermal expansion between the two components. Check the seating/sealing at the ends. There may be a corrosion crevice that opens up when the al-housing is expanding more than the cooled bronze tubes. Another possibility is that the inlet filter has been soaking wet due to storage or leakage; the blower will spray that water onto the tubes. Finally it's dropping down into the no 4 intake.

    Have no key to production years, you have to check with a Merc shop. As these engines come from Italian VM-diesels, you may be better off to call the VM factory directly; they have given good service to me with very little "burocracy".
     
  6. ruurd
    Joined: May 2011
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    Location: Netherlands

    ruurd Junior Member

    I will open up the cooler to check if there is any sign of corrosion. I have to find the cause of this valve failure before I assemble it again.
    Maybe temperature and vibration together caused it to leak.
    I never saw an inlet valve cracked like this due to a hydraulic lock. Mostly the conn. rod will bend instead.

    To my knowledge the filter was dry when the valve cracked. To me it's even more strange that it happened when the engine was running ~35 minutes. I mean when there is a small leakage this will evaporate during combustion. After the failure I had to continue for ~20min (on lower rpm) back to port.

    Even if the cooler was leaking how do I prevent it from happening again? After repair there is always an possibility that is starts leaking again or is there an improved design available?

    I will try to contact call the VM factory to get some more info on this engine.
     
  7. Aliboy
    Joined: May 2011
    Posts: 39
    Likes: 2, Points: 0, Legacy Rep: 19
    Location: New Zealand

    Aliboy Junior Member

    It may not be relevant to your engine, but we recently had an issue with water in the rear cylinders of a Mercruiser (VM) 4.2l 220hp. That was from a crack in the water cooled turbo exhaust housing leaking back into the lowest cylinders through the exhaust manifold.
     

  8. CDK
    Joined: Aug 2007
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    Location: Adriatic sea

    CDK retired engineer

    A birth defect cannot be ruled out completely. What started as a small crack can slowly grow, aided by moisture and temperature gradients until the part is weakened and the process accelerates.

    It took the 300 hp V8 in my Glastron-Carlson almost 90 engine hours to sever a piston rod, causing the piston to hit the head with such force it pushed the valves and seats through the head and snapped the camshaft. The underlying cause turned out to be a casting fault in the piston rod with a number of minute cracks that slowly expanded.
    Mercuiser declined a warranty claim because the period was exceeded by a month, but insurance covered it .
     
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