Cummins NT855 - TBO

Discussion in 'Diesel Engines' started by MBMarine, Nov 10, 2015.

  1. MBMarine
    Joined: Dec 2008
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    MBMarine Junior Member

    Hello all,

    Does anyone have experience with the Cummins NT855 (350 hp) and would be able to tell me what the typical time between overhaul is for this engine? It's a 14 L/ 6 cyl heavy duty engine, so I guess it will last for more than a few thousand hrs, but I would greatly appreciate a more specific number.

    I have been googeling and searching to the best of my abilities, but without result.
  2. whitepointer23

    whitepointer23 Previous Member

    At 400 hp they were good for 10,000 hours. 355 hp in a boat should do a lot more i would think. They are good engines.
  3. MBMarine
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    MBMarine Junior Member

    It sits in a fishing vessel and has 11.000 hrs on it (no trawling or pulling heavy loads). A lot of the hours are at very low rpm or close to idle, so I doubt it has been pushed very hard. The question is does it have a year or two left before we have to look at a complete overhaul. Thanks for the input whitepointer23.
  4. powerabout
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    powerabout Senior Member

    you check them by the crankcase blowby
    legendary engine , one of my favourites
  5. MBMarine
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    MBMarine Junior Member

    Thanks :)
  6. whitepointer23

    whitepointer23 Previous Member

    What powerabout said plus an oil sample will give you a good idea of condition.
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    FAST FRED Senior Member

    Most diesel engines are far happier under modest load , not at idle.
    Low loads can cause too low a compression pressure to seat the rings.
    They get pushed from behind by cylinder pressure during the firing stroke to properly seal.
    .The cylinders can get burnished , and get smooth loosing the hone scratches that hold lube oil.

    Slobbering , lots of black goop in the exhaust system is a sign of under loading for too long.

    I would see how much white smoke comes out the exhaust after a cold start , and observe during the warm up UNDERWAY when the smoke leaves.

    If the coolant is over 140F before the smoke clears , a compression check is in order.

    Of course the other attitude is oil is cheap.
  8. whitepointer23

    whitepointer23 Previous Member

    It will be under load . Probably propped for low revs. 11000 hrs so far so it must be set up right.
  9. WestVanHan
    Joined: Aug 2009
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    WestVanHan Not a Senior Member

    I've known of a couple of these in fish boats with a lot more hours than that.
    That said, it'd be worth spending money to have it checked by someone who knows them.

  10. Marie Espagne

    Marie Espagne Previous Member

    I worked for Cummins in the 70s
    This is one of the most successful engines ever built for marine for bulldozers for trucks it is a lovely motor at four hundred thousand miles in trucks we would turn the bearings over that is the big end bearings reversing the shells @ 400000 miles which is about 4 years we would do the liners the major weakness was electrolysis around the line of bottoms it is a marvelous engine thoroughly under rated a wonderful piece of gear I can rebuild one in my mind so easily 20 thou inch end float on the crankshaft and so on

    Timing is achieved by shims on the lifters; offset keys on the cam
    heqds are three sets of two
    the pt system pump at 180 psi up to the injecters and from there full pressure is actuated by the cam driven pushrods on the injecters
    ah memories of this engine
    15 sixteenth inch head caps plus 400 ft pound torque, I cannot remembrer exactement
    be cAREFUL? SOMETIMES THE PUSH RODS FILL WITH OIL you can heqr the dull sound when tapped

    in marine 20000 is not unusual
    this config, ie bore stroke was , is used for the vee 12 16
    im me for details how to serive rebuild this wonderful motor, I did about 100 of them
    be sure to rip apart the oil filter, to READ the engine, if there is excess metal there, when you rebuild you will need replace the oil cooler element as it is impossible to flush it

    I also remember whilst working at Cummins; we had expected a lot of rebuild work at 16000 hrs for the 1710 which is basically an 855 in vee, it never came
    they just kept on running
    and this was mines work, dusty open cut stuff
    one thing in a rebuild, is to check your liner height as the counterbores can wear a little, brass shims are then fitted under the liner lip as it seats on top of the block
    when these engines first arrived on the scene, they were well ahead of Californias emissions standards
    running an 8v gemmy on the dyno and then a 903 cummins we got 6 miles per gal, the gemmy got 2.5

  11. rayman
    Joined: Sep 2009
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    rayman Senior Member

    In this country, (Australia) there have been quite a few line-haul trucks do a million miles(not K's) with those engines.Very high hours in them and the V1710 in mine-field gensets too.As mentioned above, do S.O.S. (scheduled oil samples) to gauge engine wear.
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