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M939A1 fuel in oil saga

6

67hotrod

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Hey guys, I’ve been fighting getting fuel in the oil on my 923A1 NHC-250 and thought you might like to see the saga, as it’s not over yet!

I got all the routine maintenance and needed fixes done after I got it the first of the year. Got it ready for the road, and noticed after the first trip that it might have had a little more oil than I remembered. Made a second trip of maybe 20 miles, and the oil level gained about half an inch on the stick. Panic!!!

Took it to a diesel shop thinking it needed new O-rings on the injectors, as it had been setting for close to a year between starts for a couple of years. They ran a dye test, but didn’t see any evidence of it leaking under the valve covers, but then again it only leaked out on the road under full fuel. Put in O-rings, still did it. They said it was then the front seal on the fuel pump that was letting it in through the timing cover, and they could tell that was where it was coming from. OK, fine, got a fuel pump on the way. Put it on and oops, no change!
The next step was to replace the injectors, they looked for cracks from the injector hold down bolts into the bosses and didn’t see anything. They said they were around $140 a piece, so why not, we’re starting to run out of things to try. Turns out that they were $300 a piece, and they had to get the new style hold downs as they are the top stop style injectors. After installing them they adjusted it with the wrong method, outer base circle vs. inner base circle, and it was apparently smoking like crazy at idle and the EGT’s skyrocketed. After driving it, yes you read that right, they decided something wasn’t right. They adjusted them again, and was apparently better. I sent them a link to Will Wagner’s nice write-up on how to adjust them.

Went to pick it up, and it rolls grey smoke at idle, and has a rough idle now. They didn’t seem to think it was a problem somehow… The pump I got came off of a running truck, and is set for only 10% over stock.

I think it’s getting ready to go back over there and have them start blocking off the injectors one at a time and see if hopefully one is just bad. If not it may need a whole new set!

I attached a video to show how it smokes at part throttle.
View attachment 20180920_184852.mov

I've got almost as much in this one shop bill as I do the entire truck!
 
1

162tcat

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Washington
67hotrod said:
Hey guys, I’ve been fighting getting fuel in the oil on my 923A1 NHC-250 and thought you might like to see the saga, as it’s not over yet!

I got all the routine maintenance and needed fixes done after I got it the first of the year. Got it ready for the road, and noticed after the first trip that it might have had a little more oil than I remembered. Made a second trip of maybe 20 miles, and the oil level gained about half an inch on the stick. Panic!!!

Took it to a diesel shop thinking it needed new O-rings on the injectors, as it had been setting for close to a year between starts for a couple of years. They ran a dye test, but didn’t see any evidence of it leaking under the valve covers, but then again it only leaked out on the road under full fuel. Put in O-rings, still did it. They said it was then the front seal on the fuel pump that was letting it in through the timing cover, and they could tell that was where it was coming from. OK, fine, got a fuel pump on the way. Put it on and oops, no change!
The next step was to replace the injectors, they looked for cracks from the injector hold down bolts into the bosses and didn’t see anything. They said they were around $140 a piece, so why not, we’re starting to run out of things to try. Turns out that they were $300 a piece, and they had to get the new style hold downs as they are the top stop style injectors. After installing them they adjusted it with the wrong method, outer base circle vs. inner base circle, and it was apparently smoking like crazy at idle and the EGT’s skyrocketed. After driving it, yes you read that right, they decided something wasn’t right. They adjusted them again, and was apparently better. I sent them a link to Will Wagner’s nice write-up on how to adjust them.

Went to pick it up, and it rolls grey smoke at idle, and has a rough idle now. They didn’t seem to think it was a problem somehow… The pump I got came off of a running truck, and is set for only 10% over stock.

I think it’s getting ready to go back over there and have them start blocking off the injectors one at a time and see if hopefully one is just bad. If not it may need a whole new set!

I attached a video to show how it smokes at part throttle.
View attachment 742233

I've got almost as much in this one shop bill as I do the entire truck!
Click to expand...
Lesson here is don't throw parts at a problem and done blindly trust a "mechanic".


Sent from my iPhone using Tapatalk
 
73m819

73m819

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Did the engine get HOT before it was parked, OR is there a chance it FROZE, if it did either, you could have a cracked head, and only wide open pressure will push the fuel though the crack, the warmer it gets, the faster the the fuel is dumped into the oil.
 
WillWagner

WillWagner

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Looks like they did things wrong up top by the way it smokes. Why did they NOT put like for like injectors back in? Top stops are fine, but i'm not understanding why they had to change to a totally different type. If they did the overhead wrong and set the injectors too tight/not in the correct place, the cups of the injectors are now cracked, or, they STILL don't have the overhead set correctly.

OR

The overhead was set wrong, weather the accessory drive is out of time or their own lack of knowledge, and the lower follower pins or shafts are broken.

Did the engine run normal BEFORE your trip to the repair facility? If so, IMHO, they have had their chance and screwed up, I would inform the people you took it to that you are taking it somewhere else and whatever they screwed up on is on them.

Google-Fu says this place is near you.

Cummins Sales and Service
4.4 (19) · Truck Repair Shop

4915 E 32nd St
(417) 623-1661
Closed ⋅ Opens 7:30AM Mon
 
simp5782

simp5782

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WillWagner said:
Looks like they did things wrong up top by the way it smokes. Why did they NOT put like for like injectors back in? Top stops are fine, but i'm not understanding why they had to change to a totally different type. If they did the overhead wrong and set the injectors too tight/not in the correct place, the cups of the injectors are now cracked, or, they STILL don't have the overhead set correctly.

OR

The overhead was set wrong, weather the accessory drive is out of time or their own lack of knowledge, and the lower follower pins or shafts are broken.

Did the engine run normal BEFORE your trip to the repair facility? If so, IMHO, they have had their chance and screwed up, I would inform the people you took it to that you are taking it somewhere else and whatever they screwed up on is on them.

Google-Fu says this place is near you.

Cummins Sales and Service
4.4 (19) · Truck Repair Shop

4915 E 32nd St
(417) 623-1661
Closed ⋅ Opens 7:30AM Mon
Click to expand...
I supplied the injection pump. They did not know the difference between top stops and non tops. When they had it together a few weeks ago after they swapped the pump the tech I talked to said that it raised the oil on the dipstick about an 1/8" after driving it hard for 10mins. Said nothing about it smoking at all much less that bad. So it is in the overhead
 
6

67hotrod

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I appreciate all of the helpful replies! They said that Cummins only listed these injectors as available replacements, so that's when they ordered the new hold downs for it. It was after this when it started smoking apparently.

The tech mentioned that he set the preload to 16 In lbs per the book, but that's not what I'm seeing on here. Could being a little loose make it smoke? Assuming the injectors were adjusted with the wrong method, or out of time, and cracked the cups or springs, is that something that will go through the engine and cause any damage? The follower rollers being broken sounds like a disaster in the making... I've rebuilt probably 1,000 engines, but they were all gas or alcohol, I'm still learning on this PT diesel injection system...

So far they are OK with working more on it on them, not sure I'd be able to get them to pick up the tab at another shop...
 
WillWagner

WillWagner

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6 in lb is the "normal" top stop injector setting for IBC setting. IF it was set at 16 in lb using the inner base method, injector 3, valve 5, inj 6, v, 3, etc, the stroke of the injector was shortened by the amount the 16 inch lb torque took up, the top stop was not in play, injector spring compressed when it SHOULD have been at it's top stop set, possible injector, push tube, cam follower damage. If the outer base method was used, there was not sufficient preload on the plunger to keep it seated in the cup during the compression stroke/positive end of injection, most likely no damage, just a bit of soot in the cup. OR, it was set correctly either way...but 16 in lb is incorrect...and the accessory drive is not timed correctly, remember, the accessory drive timing ONLY comes into play when setting the overhead, nothing else. If the drive was removed to repair a leak at the seal, air comp mount, whatever, it can be stabbed back into the hole in any position and the engine will run fine, until the overhead is set again. It is very easy to check when doing a tune up, it SHOULD be checked every time an overhead is set, unless it is your engine and know it is correct or you are familiar with the engine and know that nobody has worked on it.
 
WillWagner

WillWagner

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Another "thing" small cam, non top stop engines were known for for dillution was a failed cam lobe.

A little history.....
The reason TS injectors came about was to relieve the pressure on the cam lobe from the non top stop injector spring pressure always riding on the lobe with force. The top stop took the spring pressure off of the lobe by caging the spring pressure with the plunger in the "unloaded" position in the injector. The top stop setting is the lift of the injector lobe on the cam, there are different profile cams for SC engines, this is going back a long time, but IIRC, .192, .198, .202, that is why it was, well is important to know that the correct injector is installed when using top stops. Cam lift for a specific engine can be found in a CPL book, it also tells you what cam key to use and what base timing is. This is where the 6 in. lb setting comes into play, it is there to put just enough preload on the spring/plunger to keep injection timing correct, loose setting causes late/incomplete injection, the cam lift needs to take up the slop in the setting and is not pushing the plunger all the way down in the cup. Same thing for non TS injectors if they are set loose. There is just always a load on the plunger and cam so you can't physically see or grab hold of the injector lever and wiggle it like on a TS injector.

OK, enough of that,

If the cam lobe/follower is failed in the typical mode that SC or most other Cummins engines failed in...the TS injector was better, cams failed less frequently, but until lobe surface finish was refined, cams still failed in the same manner...which is what is called "Macrospalling". I can't find an image on line and didn't save any of the reuse guideline books, but it looks like the craters on the moon. Eventually the roller starts skidding on the cam, cam lift goes away, the start of injection ramp is flattened out and the fuel that is supposed to be injected quickly so it atomizes, is now just kind of dribbling into the cylinder. It washes past the rings because timing has changed in that cylinder, incomplete combustion from retarded timing, usually accompanied by white smoke, and fills the crankcase with fuel.

Setting the overhead with a failed cam can sometimes rid the engine of white smoke, but you will hear/feel a miss.
 
WillWagner

WillWagner

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Didn't answer your Q's, sorry. Cracked cups can fracture into small pie piece shaped parts that can come out of the retainer, only seen that a couple of times, so that's why I mentioned it. Yes it causes cylinder and head damage. The most common thing that happens is the bending of push tubes, breaking of cam follower pins and shafts if the overhead is set tight, like would happen if 16 in lb was used when setting IBC method.
 
Last edited:
6

67hotrod

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OK, they just found their notes on it. They set it using the outer base circle method, using the 6 in lb from the inner base circle instructions. Theoretically if the drive is timed right there may be no long term damage then?

So just to regroup, we need to check the timing on the accessory drive, and set it using the IBC method torqued to 6 in lbs right? Do you happen to have some IBC adjustment instructions for dummies laying around somewhere?
 
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67hotrod

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I've read that post a few dozen times, and even sent it to one of the guys there before he did the injectors, but it apparently didn't make it to the tech that did it. I'll hand it to him myself this time... Is the OBC method any more or less accurate?

I'm glad this information is being saved on the interwebs, it is invaluable!
 
WillWagner

WillWagner

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OBC method is quicker. They need to make sure they have the correct injectors for the CPL, remember different lobe lifts. Non TS injectors and OBC don't care what the lift is, but a short top stop and a cam profile greater than the top stop will cause damage IBC or OBC. They NEED to make certain the injectors are correct.
 
6

67hotrod

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Great news, it appears to be ok!!! "We" ran the overhead, the correct way, and all of the injectors were over a round looser than they needed to be to get to the 68-72 in lbs of torque. Immediately ran, and sounded better after that. Assuming that no damage was done with them running that loose, and that the rings aren't too bad from all of the washing down with extra fuel, I should be ready to head on to the next adventure now. Thanks a million to Will, he's a good guy that really knows his stuff!!
 
WillWagner

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Very cool, keep an eyeball on the oil level and keep us updated!
 
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