Overhauling fuel injectors

Discussion in 'Diesel Engines' started by CDK, Jun 7, 2010.

  1. CDK
    Joined: Aug 2007
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    CDK retired engineer

    This was a job I postponed for over a year now because you get dirty and tired, but a friend who reverted to gasoline gave me this giant socket wrench for this job, so I made a start.

    First I wish to express my deepest respect for toolmakers like Belzer who make 1/2" extension bars that seem to be indestructible. The torque to remove and separate an injector is astonishing.

    On the internet I read a dreadful story about the need to use the proper shims and pressure-test the injectors before installing them.
    But a former employee of mine who took over his father's overhaul business said they never do that. They simply unscrew the housing, insert the new innards straight from the vial they come in, tighten the two halves with the proper torque and reinstall them.

    According to him the shims belong to the housing and the production tolerances of the injector itself are near-perfect.

    Does anybody have experience with this?
  2. baeckmo
    Joined: Jun 2009
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    baeckmo Hydrodynamics

    Can verify your friend's conclusion. Although we always check opening pressure and tightness after a nozzle/needle switch, I can't recall one single injector in need for shimming; they all come out with pressure within limits.
  3. CDK
    Joined: Aug 2007
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    CDK retired engineer

    He is not my friend: his hands and feet are twice as large as mine, but he seemed honest to me.

    Thanks for backup up his opinion Baeckmo. I will tighten them to 70 NM and screw them back in before taking a long shower to get rid of the diesel smell.

    Later this week I will concern myself with the stainless tunnel extensions I had made. Even have a pneumatic drill to work under water!
  4. Bglad
    Joined: May 2010
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    Bglad Senior Member

    I don't know if this applies to the type injectors you are working with but I was told by a Detroit Diesel mechanic that when reassembling the unit injectors out of those motors if the parts are not at about the same temperature the tolerances are so close they sometimes cannot be reassembled. Also touching the plungers could cause corrosion that could later lead to failure again due to the close tolerances. That's all I know about that...
  5. CDK
    Joined: Aug 2007
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    CDK retired engineer

    That could certainly be true under extreme circumstances and/or large injectors. Those for a passenger car come in oily plastic vials containing the injector and its needle.

    I just dropped them in their housings , tightened those and reinstalled everything. The engine is running again, better than before, so it was worth it.

    You know more about injectors than most people already......
  6. capt littlelegs
    Joined: Apr 2010
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    capt littlelegs New Member

    I was trained to do injector testing many years ago as part of my army engine fitter course where an injector test bench was used for various pressure and leakage tests but I've not had many injector problems since then. These days engineering precision is much better so you can probably get away with just replacing a part but you will never know if it is operating properly or set perfectly, personally I would prefer a complete tested exchange reconditioned injector if a cheaper cleaner or a hard run didn't cure the problem first.

  7. BTPost
    Joined: Dec 2009
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    BTPost Junior Member

    My experience is that on Modern Injectors, if you replace the Innards, keep everything clean, coated in fuel, and reassemble using the Spec'd Torque, usually things will be just fine. Injection Pumps on the other hand, absolutely need a Flow Bench, to get the setup, properly. The only caviate, I would add, is IF your injectors have had Nozzle Tips that have had some water run thru them and are even the slightest bit eroded, New Nozzle Tips will be required.

  8. CDK
    Joined: Aug 2007
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    CDK retired engineer

    BTPost, it is simpler. Bosch sells the body and plunger as an overhaul kit, the tip is part of the body. It also includes a flame shield disk which doubles as a non-reusable seal; it deforms when installed.
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