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Setting injector travel on a Cummins 855

Discussion in 'Trucks' started by CJLennon, Oct 12, 2011.

  1. CJLennon

    CJLennon Well-Known Member

    Joined:
    Jul 24, 2009
    Messages:
    62
    Location:
    Chapel Hill, NC
    Hey Folks,
    I just jumped off a previous post on how to diagnose a Cummins 855 engine miss and I got some great answers. Thanks. Now I am looking at understanding how to set injection travel. I have done a lot of reading on this forum and others but I did not find a clear explanation on how to set up the injector travel. I found a lot of bits and peices but nothing from begining to end. So, if you folks have a moment, I would like to paint this picture using my situation.
    I have a Cummins 855 NTC-400 with a manufacture date of 6/87 that is in a 1987 Ford 9000 tractor. The tag on the side of the engine identifying the valve lash is crystal clear (.011 intake, .024 exhaust) but the injector travel data states "T.S. Zero" which I have learned means Top Stop injector. I also learned that Top Stop injectors have a flat washer inside the injector (shake out the center part so you can see it) that holds the spring in place. I also learned that you can't use the travel (dial indicator) method to set these injectors up. You must use the torque method.
    What method you have to use (I must use the torque method), you might as well set/check the valves also at the same time as long as you have the Jake (if equipted) off. BUT, there is a difference and the difference has to do with what injector you are setting. If you use the travel method (non-top stop injectors), you want to set the injector on the cylinder that is one BEHIND the cylinder on which you are adjusting the valves. For example, if you are adjusting the valves on cylinder #5 because the pointer is pointing to the "A" on the pulley and both valves on #5 are loose (i.e., #5 on TDC compression stroke), then you need to be setting the travel on injector #3 (i.e., 1-5-3-6-2-4). If you are using the torque method, then you need to be setting the SAME injector as the valves you are setting/checking.
    With the travel method, they have you setting the travel on the injector just before it starts to go into its travel (if you are setting valves on #5, then the engine is TDC at #5 on the compression stroke and #3 is right behind it but just before the injector starts its travel). With the torque method, the idea behind it is to bottom out the injector on the cylinder that is TDC on the compression stroke so you are actually making sure that the injector is in the proper position (closed tight against the seat) for TDC. When you think about it this way, you are taking any wear on the cam out of the equation because the push rod assembly is sitting on the high lobe of the cam giving you the actual lift you will see once the engine is running. From what I understand, Cummins indicates through a service bulliten from years back that this is a more accuarate method. Besdies, with top stops, you don't have a choice. You have to use the torque method.
    So, the reason I typed all this in is to get you Cummins experts to verify that I got it right and for the next poor slob that used to be a gas engine guy like me and thinks he's a diesel mechanic, so that he doesn't spend a good part of his life trying to figure out why one of these Cummins REALLY smokes or has a miss. So, any takers to verify that I finally got it right? I owe you folks BIG time. Thanks!

    Chris
     
  2. CJLennon

    CJLennon Well-Known Member

    Joined:
    Jul 24, 2009
    Messages:
    62
    Location:
    Chapel Hill, NC
    Opps! Screwed up. Let me add a correction. For top stop injectors ONLY, you do the previous injector from the valve that you are adjusting just like you do for the travel method with the dial indictor. The only time you do the SAME injector as the valves is when you are:

    1.) using the torque method

    2.) the injectors are NOT top stop

    So, did I finally get all this correct?

    Chris
     
  3. CJLennon

    CJLennon Well-Known Member

    Joined:
    Jul 24, 2009
    Messages:
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    Location:
    Chapel Hill, NC
    One more note. Don't ever try setting top stop injectors using the travel method. I'm here to say that it does NOT work! It turns out that each injector is about two turns of the screw too tight and needed to be backed off these two turns. Now, that NTC-400 purs like a kitten (and still smokes like wet wood). Thanks to all!

    Chris
     
  4. 1080 bobcat

    1080 bobcat Well-Known Member

    Joined:
    Dec 18, 2010
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    94
    Occupation:
    self employed mechainc
    Location:
    toccoa ga
    You dont adjust the nut on a top stop to set the injector you will mess the calbertion up to set one you just torque it down to 6 in pound all you are doing is elimating the free travel on the push rod. you probly done mess the nedlee and seat up in the injector because excessive injector travel i seen them have the end punched out be set wrong. Older cummins used the torque method to set the injectors the injector had to be on tdc then you torque it down to spec.
     
  5. mechanic3

    mechanic3 Member

    Joined:
    May 26, 2013
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    Occupation:
    Mechanic
    Location:
    Fiji
    Im working on a cummins engine; Model NT855-C250 or is it 855 NTC 250 ? Engine number is 23104864. S.O number is7487 and Date of manufacture is 1972. Anyone can help me know how to set the injector timing using torque method ????
     
  6. Old Junk Man

    Old Junk Man Well-Known Member

    Joined:
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    Occupation:
    retired
    Location:
    11143Hwy 90 West Pocahontas Arkansas 72455
    On top stop injectors I simply remove all slack from the rocker when at the proper timing sequence. then tighten with a screwdriver 1/4 turn. When they first came out We didn't own a inch pound torque wrench. It worked for me and I done it that way for 40 years.
     
  7. kshansen

    kshansen Senior Member

    Joined:
    Mar 11, 2012
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    Retired Mechanic in Stone Quarry
    Location:
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    I'm going to guess that this engine does not have top stop injectors. I thought I might have a manual at home but what I have is actually too old!

    I did find a Cummins service manual online that may help. You can view it here:

    http://www.slideshare.net/hrobertdm/megafileuploadnta855-work-shop-manaul

    It appears to be a copy of a US Navy manual and has just about all Cummins engines of 1980 and before so there is a lot to scroll through but if yo go down to page 2-36 or so they show the torque wrench method and there is the dial indicator method shown a bit before that. I always preferred the dial indicator method and even if you don't have the official tool if you understand what is being done you should be able to do it with just about any dial indicator and a little creativity on the mounting. Just need to be able to extend the end of the dial indicator so it can reach the top of the plunger right above the spring.

    Hope this gives you something you can work with. If I find some better directions I'll post them, or maybe some one has an early 1970's manual handy
     
  8. td25c

    td25c Senior Member

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    indiana
    Yup , Use the same method . Works fine .
    https://www.heavyequipmentforums.co...engine-repower&p=180679&viewfull=1#post180679
     
  9. repowerguy

    repowerguy Senior Member

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    Mar 18, 2015
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    Occupation:
    mixer truck mechanic
    Location:
    United States southern Ohio
    A Cummins dealer and friend told me that all a normal man can turn with his thumb and index finger on a screwdriver handle is 5 in pounds! That's how I do them and I do have the proper tools, this way is just faster and accurate enough.