Diesel in crankcase

I’m looking at a military 5 ton with a nhc 250 cummins in it. (non turbo/no injectors).
It has diesel in the crankcase the owner believes gets there via the fuel pump drive but the diagram i have of the pump shows only a flat gasket at the end of the idler gear where it could leak as the drive gear is on the suction side?
It hasn’t run in 2-3 years and I won’t consider making a offer till i know the engine runs so I told him i’d see if it’ll run. where besides the fuel pump could diesel get into this engine?
I know such engines are not aboard ships (that i’ve been on) but maybe one of you has ideas?

Leaky injector could cause that over a few years leaking past the piston rings… I’d still suspect a fuel pump

yea, i keep getting caught by that too but there are no injectors. I can’t see any other place for a fuel/oil interface. some engines had a booster pump on the side of the block but this one evidently has just this geared positive displacement and a 5/8" line to the tank, and no electric pump in the tank that I could see.

So fuel got into the crank case while it was sitting?

Leaky fuel return line under rocker cover?

all fuel lines to engine on outside, no fuel rail, no turbo, no injectors. the military 5 ton was used feeding cows mostly during winter so didn’t travel further than probably 300 yards from barn. on its last trip it got to smoking and that’s when they found diesel in crankcase, they got it most of the way back to the barn and he said it sounded like the fan belts were squeeling and it quit running. the engine had been overhauled as the previous engine got a rod thru the block. (I DIDN’T ASK!!) so it only got used to feed cows in the morning for about 15 years so it doesn’t have jack on it for mileage or time. i’d guess it took maybe a hour or a bit more to feed for 5 months of the year. This truck was a engineer truck with a gantry for bridge moving on the back so it has a ten ton pto on the front and a 20 ton hydraulic on the rear with the associated gantry. I intend to use it to haul logs to my sawmill.
Iam hopefull that because of the low engine use, low rpm use, flat ground operating that the inserts are still good but i need to get new oil in it and have it run a while to insure the insides are ok. it has a block heater on the water system so it was somewhat warm when it was started in the winter.

Can someone explain a diesel engine with no injectors???


Pop 1 of the 3 valve covers, pretty sure your going to find a mechanical injector / rocker in there.

This could be one of those external combustion engines.


in my experience and ive done several engine failures on the 555 cummins, the injectors seats are probably worn. i had one bad runaway after rebuild from not seating the injectors propeller in a couple of cylinders. about 2 gallons of diesel found in the crankcase

ok barge monkey, i’ll look at that side of the engine. I too found it improbable to be normally aspirated. (stay tuned) i hope you’re wrong bruce 1, recall this engine has very little time on it since overhaul. i have good diagrams of the fuel pump and while possible, i have a hard time accepting gallons of fuel went thru the air compressor crankcase to get into the engine but that
is the prevailing theory. I shall consult a couple sources before ordering gaskets and such for the fuel pump, I sure don’t want to R&R injectors in the field either … in the snow !!!

I dont speak enough cummins to know about the earlier stuff, been around an N14, have a 4BTA in a slasher, 6BTA in a 460C, 6.7 in my Tigercat 620C, havent gotten stupid deep into any of them myself, just sold a buncher that had a mechanical 8.3, new one thats coming has the 300hp QSK? which Im afraid to price parts for. Had a similar issue with fuel dilution / in the base with a 3306 on a D6C a few yrs ago, injector cups / seals. Im not home to look, I believe youve got the same engine thats in our antique yard crane, have to see if Ive got a book for it.
Guy down the road from me has one of the multi-fuel “white engines” in his army truck, kind of neat, helped him change a winch one day on it.

RTFM Grasshopper, enlightenment awaits.

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it’s looking like i may be the one who needs enlightening, I’ll be calling the parts dept. soon enough, on my first visit to that truck there is a lot I didn’t see I imagine!
Nice crane barge monkey, it looks like you’re in the SE? i’m in the PNW. i guess visiting your junk yard isn’t going to be practical.

Immaculate injection


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that;s very impressive steamer, I’ll no doubt find mechanical injectors on the stbd. sided of that engine … Not like my hatz water pump diesel ! or is it?

its an 855 ya?

i never found a tag on the engine but the parts house only wanted the tag inside the cab, it was way too damn cold to get under the truck or move around much, i figured i had the info they needed. i took pics but the fuel line didn’t show where it evidently goes into the block so i guess it has mechanical injectors like my old dozer. this was my second visit, i expect 3rd time to be a charm