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Annoying knocking sound

Discussion in '1982-Present GM Diesel' started by 4x4_76, May 14, 2002.

  1. 4x4_76

    4x4_76 1/2 ton status

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    A week ago my K5's engine started to make some sort of knocking sound.It's not constant.First I didn't know where it was coming from.After little searching,I located it to a cylinder #2.I went under the truck,and by using long screwdriver,I tried to listen from the oil pan that was the sound coming there.Nothing.
    Then I listened from the valve cover.And it was definetly #2.I loosened injector line and the sound was gone.Tightened the line,and the knocking sound was really loud.
    Engine runs smoothly on idle.So I guess it can't be bad
    injector.
    Previous owner had changed one piston,because it had broken,abowe the pin.It was just went pieces from there.But if this is the source of that sound,I could hear it from oil pan,too?

    What could be the problem?Lifter?
     
  2. René

    René 1/2 ton status

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    Oh, oh! That doesn’t sound very well!
    Normally I would have said, that it would be a problem with the injection nozzle. But since the noise comes mainly from the oil pan, I fear a bearing failure or a broken crankshaft.
    Does the noise change if you accelerates or retards (load changes) the engine?
     
  3. 4x4_76

    4x4_76 1/2 ton status

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    <blockquote><font class="small">In reply to:</font><hr>

    I went under the truck,and by using long screwdriver,I tried to listen from the oil pan that was the sound coming there.Nothing.

    But if this is the source of that sound,I could hear it from oil pan,too?

    <hr></blockquote>

    Notice the question mark?/forums/images/icons/wink.gif

    My brother was also thinking that it might be the injection nozzle.But it runs smoothly,don't shake at all.Is it still possible that nozzle is bad?

    Noise varies with the RPM.On highway speed I can hardly hear it.
     
  4. René

    René 1/2 ton status

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    Yes, because the engine has a very large rotor, it runs nevertheless smoothly. A singel nozzle, which makes problems, you can only hear at a hard noise. To open a line is a good possibility to find the error (and it seems to be like that in your case), but tries to ‘feel’ the lines. You would have to feel clearly stronger vibrations at line #2, if the nozzle drips…

    The other side is: A broken connecting rod bearing is also calm, if no load is on the piston...

    Can you exchange one nozzle by another? Then you could hear immediately, if the noise arise now in another place...
     
  5. 4x4_76

    4x4_76 1/2 ton status

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    My brother has a set of rebuild,low mile nozzles.I changed one on #2,and I could still hear that knocking(or tapping) sound.
    I also noticed that I can hear it only from the head.I tried to listen it on top of the block,just above the lifters.Didn't hear a thing.
    Then I listened on top of the head,above exhaust passage.Very clear knocking from there.
    Maybe I should do a compression test.I was thinking that could it be the exhaust valve?Or broken rocker arm?
    Anyway,I have to make adapter for the compression test gauge.
     
  6. René

    René 1/2 ton status

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    Now the error can go into two directions. 1.) a problem between injection nozzle and pump starting from the distribution. 2.) mechanical problem above the piston.

    You can actually exchange the first problem only through the various parts (line, pump) to locate. Second is more difficult. Remove first the valve cover and control whether all parts at the correct place and is intact. If you find no error there, you can see with an endoscope into the combustion chamber. If you cannot procure such an equipment, you must decrease the cylinder head. As defects the following topics occur to me: 1.) broken pre-chamber cover 2.) broken off glow plug 3.) broken piston ring

    It surprises me only that the noise does not come now no more from the oil pan???
     
  7. 4x4_76

    4x4_76 1/2 ton status

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    It's not the nozzle,nor it's broken glowplug.Injection pump is rebuild,has only about 250 miles on it.
    Just the other day that sound strangely vanished,but yesterday I could hear it again.
    Oh well,I guess I first pull the valve cover,and if everything is ok there,I take of the oil pan and make sure there is nothing wrong.
     
  8. arveetek

    arveetek 1/2 ton status

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    GM diesels have a tendency to get sticky lifters. I tend to get a sticky lifter after towing my fifth-wheel more than several hundred miles. It usually goes away once I get back home.

    Last year it got really annoying, so I used a trick to loosen it back up. I poured a quart of tranny fluid into the engine oil, ran it about 200 miles, and then changed the oil. Cleared it right up, and hasn't been back since.

    Casey
     
  9. Rondo

    Rondo Registered Member

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    I had a similar problem in my 6.2. It had a topend rattle sound that would come and go. It was worst when the engine warmed up. I took it to the Chev dealer and they thought it was a bad wrist pin. I drove the truck until it was almost out of fuel. Filled it back up and the sound was gone!! I haven't heard it since. I think I got some bad fuel. [Like it had gas in it] How long has your truck been making this sound?
     

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