Daño en Motor Caterpillar 3406C Bulldozer D8N

Daño en Motor Caterpillar 3406C Bulldozer D8N

en su experiencia que creen que pudo ocacionar este daño en la valvula y a su vez al piston. 

34 Replies

  • estos equipos utilizan Mobil Delvac MX 15W-40 CI-4 Plus con intervalos de drenado de 350 horas.
  • I think this valve is the fuel valve ,and it was broken first, which increased the amount of fuel and damaged the piston.
  • THE valve could be hung , which led to a stroke by the piston ,and breaking this part of it .
  • the problem isn't obvious. could you please explain some more.
  • images show very high level of residue on the piston and valve block. but to be sure, the first image is for the piston and cylinder right?
  • In reply to Mahmoud Amer:

    gracias estimado, el aceite tenia demasiada dilucion por combustible, yo atribuyo el daño al sistema de inyeccion, salvo su mejor opinion.
  • Jose - I want to thank you for posting this as it gives all in the Club a chance to learn. To solve this problem - let's write down what the photos tell us:

    1. The exhaust valve failed or fractured.
    2. The intake valves (larger) do not appear to be seated correctly
    3. There is debris denting on the head.
    4. The piston is deformed, there is oil in the bowl and there are score marks on the clylinder.
    5. The cylinder liner score marks suggest the rings may be stuck.

    OK - what does this tell us:

    1. Exhaust valves typically fail due to excessive localized heat in this case, due to bad seating.
    2. I suspect that as the valve fractured, the exhaust gases that escaped were drawn back into the cylinder and recompressed. When this occurs those hot exhaust gases get even hotter on recompression.
    3. As the exhaust gases get hotter, keep in mind they are in the cylinder, they would melt and deform the piston.
    4. As the piston deforms, metal comes free, denting the cylinder head.
    5. Debris would also score the liner and get behind the rings causing them to stick.

    Possible causes:

    The cause that sticks out the most is improper valve seating. If you look at the picture above three of the valves are not seated properly. This has numerous causes:

    1. High hours on the engine. You don't mention the hours. The chrome plating on valve stems is not very thick (7 um) and may be worn out.
    2. Poor machining of the valves. Clearance should be 0.0002".
    3. Use of wrong valve stem seals or seal failure. Oil in the piston bowl suggests stem seal failure.
    4. Wrong type of valve alloy used.

    Possible way to prevent:

    1. Make sure to get valves from Catepillar. After market valves are often less expensive but do cause performance issues.
    2. Get a new head from Catepillar.
    3. Make sure the stem seal is correct.
    4. Make sure valve and seat clearances are correct. Stellite faced valves are often used to handle high exhaust temperatures and should be used in this case.
    5. Have your Caterpillar Dealer oversee the rebuild. They will make sure that compatible materials are used and . proper clearance are set.
    6. And of course use Mobil Delvac products.

    I hope this helps.

  • In reply to Mahmoud Amer:

    First image show the piston essentially starting to melt. Due to High heat.
  • In reply to JOSE HIGUERA:

    The injection system was not the cause. It did it's job.
  • In reply to younes:

    Your are correct in that is a valve issue. As the broken valve allowed for recompression, high heat and debris denting of the head. Well done.
  • In reply to younes:

    The broken valve is an exhaust valve. It increased the heat in the cylinder not the amount of fuel.
  • In reply to JOSE HIGUERA:

    The amount of hours on the engine and how it is being used would be helpful. Generator, mobile equipment, etc. If this engine had high hours the failure might be acceptable. If new, then there is a maintenance issue.
  • In reply to Rick Russo:

    el motor es de un Bulldozer Caterpillar D8N equipo movil, esta maquina tenia 14,000 horas de trabajo.
  • In reply to JOSE HIGUERA:

    A damage to the fuel system shouldn't dilute the oil. A damaga to the oil and pressure rings causes that.
  • In reply to Rick Russo:

    I thought these were deposits or scale on the cylinder's perimeter.
  • In reply to Rick Russo:

    I agree with you Mr Russo.
  • In reply to Rick Russo:

    If the exhaust valve is broken, then there should be no compression and very bad combustion. thus the heat inside the cylinder should be decreased not increased.
    Isn't that right? or you have another point of view about it?
  • In reply to Rick Russo:

    I believe wrong sitting of the valve is the cause of this issue. It caused thermal stresses on the valve and caused the thin edge of the valve to crack.
    But the thermal stresses occured before the cracking of the valve not after. Because after the crack the cylinder is no longer sealed and it became an open system during the compression so no compression is possible.
  • In reply to JOSE HIGUERA:

    I believe the recommended hours for the valves is in the range of 20,000 right?
  • In reply to Rick Russo:

    SR. RUSSO, TODO ESTO QUE DESCRIBE ES DE GRAN AYUDA PARA NOSOTROS.. GRACIAS
  • In reply to Rick Russo:

    Lo que se me hace raro es la gran cantidad de diesel en el aceite al momento de desarmar el motor.
  • In reply to JOSE HIGUERA:

    maybe when the damage was done, the seals were damaged or the gaskets. Or even the piston as it seems to be badly damaged.
  • In reply to Mahmoud Amer:

    Mahmoud - Thank you for your comments. I agree with you tha poor valve seating enabled this high heat situation to occur. A couple of comments.

    Recompression is possible with a cracked valve as SSA (swept surface area) on the compression stroke, squeezes the gas faster than it can exit the crack in the valve. You are correct as the recompression achieved will be less than the designed compression. Lets say the exhaust gases are drawn into the cylinder through the valve crack, these gases, depending on the application can be between 750 - 1100 F. You recompress them and the temperature goes up. That is the heat event that most likely cracked the valve and caused the piston crown to deform.
  • In reply to Mahmoud Amer:

    Depends on the application. If the 3406 is in a on or off highay vehicle - I would expect 10,000 hours from the head. If it is in a natural gas application, I would expect 20,000 to 25,000 hours.