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dd 671 ti

Discussion in 'Engines' started by about time, Jan 19, 2015.

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  1. about time, Jan 19, 2015
    #1
    about time

    about time Member

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    On my dd's I have the old style injector rack. That is to say the tube that actuates the injectors has two adjusting screws per injector as opposed to the new style which has a spring on one side. What are the advantages of having the new style? They would cost me approx. $300.00 each, I would need 2, one for each engine. Is this in any way related to preventing runaway? If an injector hangs up at cruise, will the solid rack prevent the engine from idling down? I would like to know the theory behind the spring style rack.
  2. Capt Ralph, Jan 19, 2015
    #2
    Capt Ralph

    Capt Ralph Senior Member

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    The solid rack will not come back if an injector completely locks up, the spring load rack will bring the other injectors down.
    A spring loaded rack will bring all else down but a lung will keep trying to make power.
    I have never heard of a locked up injector not able to be pulled down by a hard rack. I guess it could happen.

    That's why you have a shut down flapper on top of the air box. You do have a emg shut down flapper?
    Stif injectors show themselves by loping at warm idle. The governor will only push so much and a half second late on a stiff rack. Buffer spring can only do so much. If you have a bad injector dragging, you would know something is up before total lock up (again, never seen a complete lock up).
    My self; I would prefer the 2 screw rack (I was raised on 2 screws) and old racks.
    During my tunes, I can bring a 2 screw bank in perfect just by leaning on the lock nuts. The timing tool just rides on the spring top ah so sweet. Many hours their still in place.
    Takes a few extra minutes on the spring load rack as I'm constantly rocking and checking. There is room for slop and you aim for the best.
    I can not tell you if any performance is lost or gained with either rack.

    Bad runaways are usually caused by a bunch of other stupid and poor maintenance issues, Keep those shut down flappers in check. Spend that money in proper maintenance schedules and services.
  3. about time, Jan 20, 2015
    #3
    about time

    about time Member

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    I do have a E flapper in good working order. I am experiencing a warm idle loping, not consistently, never under load. How can I determine which injector may be stiff? I have two spare N95 injectors rebuilt by DD. It may be relevant here to confess, she is a dock queen. Only ran tied to the dock every weekend, engines brought up to temp, one at a time in gear at idle, then no load wot briefly. Think this issue will go away when she gets ran in the spring?
  4. Capt Ralph, Jan 20, 2015
    #4
    Capt Ralph

    Capt Ralph Senior Member

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    Ya gotta get her off the dock before any loping idle concerns come to point. I am not a fan of dockside warm ups. Head temps and pressures will never come up tied to a dock.
    One of us is in your hood. I'm in Jax. I'm sure a few of us are closer. Put on some coffee and lets go put a cruising hour or two on them.
  5. P46-Curaçao, Jan 20, 2015
    #5
    P46-Curaçao

    P46-Curaçao Senior Member

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    I recently changed to the new model racks, and why not?
    Why not prevent any risk for $500…I did, and FYI, PC Industries LLC in Wyoming has the on stock.

    Furthermore, a non or not correct functioning injector is easy to detect, just get the valve cover off, put a towel on top of the cylinder head (to prevent oil spills), start the engine and push, with a large screw driver, on each injector. If the engine is not idling different, you injector is not OK.
  6. mwwhit1, Jan 20, 2015
    #6
    mwwhit1

    mwwhit1 Senior Member

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    Before even taking the valve cover off, I use an IR gun to see the temp of each cylinder's exhaust as the engine warms up. Easy way to see how each cylinder compares and where to look first.
  7. P46-Curaçao, Jan 20, 2015
    #7
    P46-Curaçao

    P46-Curaçao Senior Member

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    I agree, but is not specific how to test an injector...
  8. jhall767, Jan 21, 2015
    #8
    jhall767

    jhall767 Senior Member

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    Look on youtube for a video of how to test a DD or Detroit Diesel injector. It's not hard at all.

    I'd post a link but I'm not sure if it is allowed.
  9. K1W1, Jan 21, 2015
    #9
    K1W1

    K1W1 Senior Member

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    Go for it, If it does not link to a competing site I am sure Carl has no objection.
  10. Capt Ralph, Jan 21, 2015
    #10
    Capt Ralph

    Capt Ralph Senior Member

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    Who said he had a bad injector?
  11. about time, Jan 22, 2015
    #11
    about time

    about time Member

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    Exactly!!! Engines run great! WOT no load is fine. No smoke. 2-3 loops at cold start up. Starboard engine has recently started to loop when it reaches 130 degrees on the gauge. As soon as temp comes up to 150, looping goes away. Even this is inconsistent. What Mr. RCRAPPS has said makes perfect sense. I have one or two injectors starting to hang up and delaying the proper operation of the governor. Probably due to the fact the boat has become a dock queen, waiting for her owner to make enough money to complete the next step in major renovations to the boat. At this point I believe she needs to be run to get happy.
  12. P46-Curaçao, Jan 22, 2015
    #12
    P46-Curaçao

    P46-Curaçao Senior Member

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    Now he said...LOL
    (just wanted to share some useful info, in case off...)

    Proper operating of the governor, could be limited by the bearings, I was told.
  13. Capt Ralph, Jan 22, 2015
    #13
    Capt Ralph

    Capt Ralph Senior Member

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    P46 may be referring to the tube end bearings that can be an issue also. Buffer spring and it's, rubber tip. I even found the cotter pin interfering with the linkage. Without rpms up and oil flying everywhere as it's spose to, all of the rack and contact points can get stiff. I'm sure there could be more that could cause a lope in the idle before anybody wants to blame injectors.
    Run her some. Get em hot, blow out some slobber. Come back with a big smile and brag a bit.