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6.2l suddenly knocking ****** UPDATE ******

Discussion in '1982-Present GM Diesel' started by imiceman44, Mar 24, 2003.

  1. imiceman44

    imiceman44 1 ton status

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    Hey Guys
    My friends dually 6.2l engine started a knock on one side of the engine a couple of weeks ago.
    To give some history, it's an 85 with 150k, he had just put some Restore in the oil a couple of weeks earlier and added some fuel additives that day.
    After checking, he found that the dose was doubled, and when the knocking started it was right after a big bang and a black puff out the exhaust.
    I told him to check the injectors and he did, tuns out they were opening at a too low pressure, so he gets a new set.
    Still the same knocking.
    He pulls the valve covers, doesn't have any abnormal symptoms, drops the pan, no shavings or signs of wear, checks rod bearings for play, nothing.
    Now he is going to check the compression, and I was thinking maybe a collapsed or malfunctionning hydraulic lifter.
    Before we tear off the heads and check everything, does anyone have any opinions?
    The sound is comming from the passenger side front top area of the engine, that is why I suspect valve train.
    ANy thoughts?
    Thanks guys.


    UPDATE: 03-26-03
    Well After changing the injectors, my friend started it and heard the knock again so he stopped it right away.
    After checking everything we discussed, and last checking the lifters and finding nothing wrong with them, he decided to put it back together, and ran it, and it's fine, smooth, no knock.
    I am guessing that there was some air left in some of the lines or the lifters were stuck and when he took them out and tested them they loosened up.
    What do you guys think of this?
    For now he's happy that it's back on the road, but he's like me, he wants to know what was wrong.
    Any guesses?
    My vote is on the injectors and air in the fuel system.
    The injectors that he replaced were opening at a very low pressure so the knock could have been from them.
     
  2. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    Re: 6.2l suddenly knocking

    Do 6.2 exhaust manifolds crack? Maybe an exhaust leak?

    Rene
     
  3. 4x4dreamer

    4x4dreamer 1/2 ton status

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    Re: 6.2l suddenly knocking

    I'd follow through with the compression check.
     
  4. imiceman44

    imiceman44 1 ton status

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    Re: 6.2l suddenly knocking

    /forums/images/graemlins/grin.gif It's not an exhaust leak.
    By the way he is a VW race engine builder, and I know a few things, so I am sure it's not.

    Any more thoughts?

    Do you think the timing could have changed on the pump?
    The marks are not perfectly aligned but rather 1/32" off.
    Would timing it make a difference.
    The only problem I have is the noise is from one side.
    Thanks
     
  5. TK5

    TK5 1/2 ton status

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    Re: 6.2l suddenly knocking

    I traced a knock on one side of my 6.2 to a piston skirt was broken off. I replaced the piston, rings and a lot of gaskets. Runs and sounds fine now. Cost $248, $68 for the piston, $59 for the rings and rest for gaskets.

    Just another place to look.
     
  6. imiceman44

    imiceman44 1 ton status

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    Re: 6.2l suddenly knocking

    [ QUOTE ]
    I traced a knock on one side of my 6.2 to a piston skirt was broken off. I replaced the piston, rings and a lot of gaskets. Runs and sounds fine now. Cost $248, $68 for the piston, $59 for the rings and rest for gaskets.

    Just another place to look.

    [/ QUOTE ]

    That was th reason I told him to drop the pan, it was a couple of days after your post. /forums/images/graemlins/grin.gif
    It wasn't that.
    NEXT /forums/images/graemlins/thumb.gif
     
  7. BlueBlazer

    BlueBlazer 1/2 ton status

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    Re: 6.2l suddenly knocking

    Try to isolate the cylinder with the problem by cracking injector lines one by one. Once youve found which cylinder has the problem, do a compression test followed by a leakdown test if the compression is bad. This will isolate a valve problem from a piston/ring problem. I would not be worrying about timing, improper timing would affect all cylinders equally, not just one. What I dont understand is the puff of black smoke, which would point to something fuel related. What Im thinking is that due to the low opening pressure, one of the injectors let way to much fuel in the cylinder and the increase in cylinder pressure may have caused something to fail. Let us know what you find.
     
  8. imiceman44

    imiceman44 1 ton status

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    Re: 6.2l suddenly knocking

    [ QUOTE ]
    Try to isolate the cylinder with the problem by cracking injector lines one by one. Once youve found which cylinder has the problem, do a compression test followed by a leakdown test if the compression is bad. This will isolate a valve problem from a piston/ring problem. I would not be worrying about timing, improper timing would affect all cylinders equally, not just one. What I dont understand is the puff of black smoke, which would point to something fuel related. What Im thinking is that due to the low opening pressure, one of the injectors let way to much fuel in the cylinder and the increase in cylinder pressure may have caused something to fail. Let us know what you find.

    [/ QUOTE ]

    I though of the same thing with the black smoke then he told me what he did with the fuel additive and I remembered one time I did the same, added too much and when I let of the gas on the highway after pulling hard for a while it did the same explosion with big black puff.
    I talked to a mechanic then and he told me it happens with too much additive and one time he had a cutomer with an exploded engine. But if the engine survived it it should be fine.
    Anyway we'll try the injector cracking method and see.
     
  9. BlueBlazer

    BlueBlazer 1/2 ton status

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    Re: 6.2l suddenly knocking

    What kind of additive are we talking here? I dont think that would have caused a problem.
     
  10. imiceman44

    imiceman44 1 ton status

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    Re: 6.2l suddenly knocking

    [ QUOTE ]
    What kind of additive are we talking here? I dont think that would have caused a problem.

    [/ QUOTE ]

    The power services diesel additive.
    It does raise the combustion temps and raises the cetane rating, a little too much is OK more then double is dangerous.
    Anyway since the pan, intake and valve covers are off already, we are going to do a compression check and then probably take off the head and examine the valve train.
    There is no point in putting it all back together to tear it appart again.
    /forums/images/graemlins/thumb.gif
     
  11. BlueBlazer

    BlueBlazer 1/2 ton status

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    Re: 6.2l suddenly knocking

    [ QUOTE ]
    It does raise the combustion temps and raises the cetane rating, a little too much is OK more then double is dangerous.


    [/ QUOTE ]
    I disagree with this cause these additives only have a certain cetane rating themselves thats not terribly high, so there is a point where adding any more doesnt change the cetane rating much, so its not dangerous. If it was there would be warnings on the bottles not to add too much. Anyway, since youve already got the valve cover off, have you spun the engine over just to see if the valve train components are moving like there supposed to and nothing is bent or cracked or whatnot?
     
  12. imiceman44

    imiceman44 1 ton status

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    Re: 6.2l suddenly knocking

    Well we spun the engine and we even took off the rockers and checked that no bent push rods.
    But we felt like some of the rockers aren't moving as much as the rest. So either Dial indicator or removing the heads and checking physically.
    Since there is no adjustment on the rockers, if lifters are bad we replace them, but anybody know how to test them?
     
  13. arveetek

    arveetek 1/2 ton status

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    Re: 6.2l suddenly knocking

    I suspect that there is a collapsed lifter, not an uncommon problem with the 6.2L, from what I have read on the DP. I had a sticking lifter on mine that caused a knock for a while. I ran some ATF through the engine oil, and it cleared it right up.

    Here is some text from a recent post on the DP about this subject that you might find useful:



    "I had to replace my pump after it sprang a leak from the throttle shaft, which led to low housing pressure, super advanced timing and ultra bad starting - sigh!
    Anyhow, I decided I might as well pull a lifter pair from the cylinder where I could hear the tappets knocking the loudest. Externally, the valve train and the 2 lifters look just dandy. I was expecting something obvious.

    Question, what keeps the end cap in the lifter pushed hard against the top of the lifter - I'm assuming a spring? If so, what actually causes them to go bad? The 2 I pulled have great roller action, with just very light wear polishing on the thrust surfaces. Everything that can be seen under the rocker covers and in the tappet chest, is beautifully clean and completely free from any gumming up or shelac (gotta love that DELO 400!)

    [ 03-03-2003: Message edited by: britannic ]


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    Posts: 220 | From: Sierra Nevada Mountains, CA | Registered: Nov 2002 | IP: Logged

    gmctd
    Contributor
    posted 03-03-2003 11:32 AM
    --------------------------------------------------------------------------------
    Several lifter types exist, but the internal wear is similar, where the barrel to piston\plunger fit is excessive, and\or the one-way-valve seating is pitted\ridged, allowing increased plunger travel before hydraulic pressure overcomes valve spring tension.
    The result - tick, tick, tappety tick.
    And etc.
    jd


    --------------------------------------------------------------------------------
    Posts: 457 | From: hou tex usa | Registered: Sep 2000 | IP: Logged

    britannic
    Contributor
    posted 03-04-2003 10:18 AM
    --------------------------------------------------------------------------------
    Thanks GMTCD! The forum comes through again; I was able to very quickly replace the pair of lifters (I wasn't sure which one was faulty, but when you go to all the hassle of getting to them, you may as well cover yourself!) without removing the heads. A flexible magnetic pickup and a flexi-claw were just the job along with 1000W of lighting (you don't actually need this much light, but I have it, so why not!) to illuminate the tappet chest.
    The engine is very quiet in comparison to it's former self, idles evenly and pulls really smooth now.


    --------------------------------------------------------------------------------
    Posts: 220 | From: Sierra Nevada Mountains, CA | Registered: Nov 2002 | IP: Logged

    suburbanz
    Contributor
    posted 03-06-2003 06:40 PM
    --------------------------------------------------------------------------------
    helo im having the same problem.yours was bad enough to effect the running?how did you know which one it was?lastly what all do you have to take of to get to the lifters and are they expensive.mine just has a little tick every now and then on the drivers side and it seems to be getting worse.any help would be appreciated!thanks owen
    --------------------

    85 Suburban 3/4 ton 6.2 n/a 3.73 33/12.50 bfg
    78 malibu 454 th350
    7.40 1/8 n/a 4.11 gear


    --------------------------------------------------------------------------------
    Posts: 34 | From: greer s.c us | Registered: Feb 2002 | IP: Logged

    britannic
    Contributor
    posted 03-06-2003 08:39 PM
    --------------------------------------------------------------------------------
    Suburbanz: First get a long screwdriver, tube or stethoscope and place it against the rocker covers to work out which bank the tick is emanating from. Once you know which bank, zero in on where the noise is the loudest. Depending on how loud the tick is (it'll sound like a hammer when you use the listening trick), you might be able to deduce which valve is affected.
    I only able to locate the cylinder, so I removed the cover, removed a section of the rocker shaft assembly, used a long extension to release the lifter retainer plate and then a magnetic pickup on the lifter guide plate for the affected tappet pair. I used the long flexible magnetic pickup to lift out the lifters (you'll need to first pull up the lifter with your magnet, that lies under the pushrod hole in the head and then flip it to the side so that you can pull it out through the larger rectangular slot."



    This information might have been useful before tearing the engine down so far. Oh well, maybe it can help now! Perhaps you could replace the lifters without removing the heads?

    Casey
     
  14. BigCUCV

    BigCUCV Registered Member

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    Re: 6.2l suddenly knocking

    couple months ago, I had a broken aircleaner hold-down bolt, it teared off right after the threat that goes into the manifold and I assume that through the engine vibrations, it was caused to unscrew itself and was sucked into cylinder No.7 where it was pushed into the Piston and knocked with each stroke against the intake Valve.
    horroble knocking Sound that was.......did only minor damage though: I replaced the in- and ex- Valves of that Cylinder and a new rod bearing!!
    drove about 10.000mls since without any signs of trouble!!!
     
  15. imiceman44

    imiceman44 1 ton status

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    Re: 6.2l suddenly knocking

    Thanks Casey.
    That is a big help, I did suspect the lifters from day one but I was dreading removing the head, now I can take them out without removing the heads.
    Now I did the compression check last night and one cylinder barely got 100PSI while the others were in the 270PSI range.
    I am thinking if the lifter is collapsed it will not open or not open enough the valves so I don't build pressure, right?
    I will let you guys know what happens.
    Oh and by the way, it's not a light tapping noise it's knocking noise, and you don't need a stethoscope to locate it, it was that obvious, and it happened in a second.
    That is what made me perplexed.
     
  16. arveetek

    arveetek 1/2 ton status

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    Re: 6.2l suddenly knocking

    I dunno...that's some seriously low compression. And I didn't realize it was such a loud knock. Hmmmmm....it's hard to say. You might end up having to remove the heads anyway. Perhaps a damaged wrist pin coupled with a hole in the piston. I wouldn't think that a collapsed lifter would make that much noise....they're usually a softer tick/knock that you can't really tell where it's coming from.

    Good luck!

    Casey
     
  17. BlueBlazer

    BlueBlazer 1/2 ton status

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    Re: 6.2l suddenly knocking

    Assuming your compression guage is accurate, it sounds like that engine is ready for a rebuild anyway. 270 psi is way below minimum specs I believe. Maybe someone else will let us know for sure.
     
  18. DieselDan

    DieselDan 1/2 ton status

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    Re: 6.2l suddenly knocking

    My manual show 380-400 psi, with anything below 380 is bad and the lowest cylinder not less than 80% of the highest cylinder.
     
  19. imiceman44

    imiceman44 1 ton status

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    Re: 6.2l suddenly knocking

    [ QUOTE ]
    My manual show 380-400 psi, with anything below 380 is bad and the lowest cylinder not less than 80% of the highest cylinder.

    [/ QUOTE ]

    Well I am going to get another one because this is one for a gasser and it doesn't go higher than that.
    From the way it ran up until that explosion, it was running more like a 350 than a 305 power wise, and that is on a crew cab dually.
    Thanks for the numbers, I will get back to you.
    /forums/images/graemlins/thumb.gif
     
  20. imiceman44

    imiceman44 1 ton status

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    Re: 6.2l suddenly knocking

    Update above /forums/images/graemlins/thumb.gif
     

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