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Discussion Starter #1
1996 12 valve cummins, 5 spd nv4500, 4x4, Borg Warner s366, dap 250 hp 5x.016, 4K gov springs, 7mm delivery valves, 60lbs valve springs, PDD lift pump 425 ARP studs

Hello all, I finally changed my head gasket and oil cooler to deal with that nagging coolant in oil issue. Upon installation of the new HG and putting the engine back together, I am having the following symptoms.
-It has a very rich smelling and looking exhaust
-LOTS of white smoke, especially when driving. I'm talking like cloud up the entire road with smoke. Stumbles off the line under any load at all.
-Sounds just horrible when driving, almost like a "knock" or a "thump"
-To my knowledge, I am not mixing any fluids, and I'm not losing any either, so I'm not burning coolant, it certainly doesn't smell sweet.
-I'm pretty sure I witnessed some liquid diesel spraying out of the exhaust right after the turbo (small exhaust leak there on the downpipe and turbo mating surface).

When I changed the head gasket, I replaced it with a .010" over Cummins HG. I did not resurface the head, as it was quite straight and passed all the tests I found in the FSM. I also changed the oil cooler (I don't think that has anything to do with the issue, but just providing all info). I did set the valves during/after the job. I got the engine to TDC with the head both off and on. When off I turned the motor with my hands on the harmonic balancer. With the head on I used the alternator pulley and turned the engine over backwards. When I got these symptoms, I checked the valves again, and also put in some different copper injector washers. Originally I had thin ones in there, I replaced with the thick ones and no difference.

I understand that with the thicker HG I lose some compression, but with the boost numbers this is supposed to run (60psi) I didn't really want to blow out another head gasket. Would the .010" really make that much of a difference? I've read guys putting it in and having a little less low end grunt and a little more white smoke at start, but nothing of what I am having. Did the motor jump timing somehow when I was turning the motor over getting it to TDC? I am obviously not burning fuel completely, but I didn't 1) increase the volume of fuel or 2) starve the engine of air somehow. I'm thinking that it has less time to burn? What could this possibly be? I am at a complete loss and have no idea which way to go or where to look. I would appreciate any help or direction. Thank you!
 

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The Uppity 12v Admin
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Timing probably slipped or was set incorrectly if you changed it.
 

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Did you adjust the timing while you had the head off?

Usually the timing doesn't slip unless its been adjusted recently. And R&R'ing a head doesn't require the injection pump to be touched at all on a 12 valve. If you're concerned about the timing its easy enough to check. But unless you've messed with it recently, I doubt that's the issue.

You may have a faulty injector, sometimes new parts are bad out of the box. You may also have a head gasket that isn't sealing combustion pressure in. Have you done a compression test on it since replacing the head gasket? If not, the Harbor Freight diesel engine compression test kit will work if you modify the dummy injector a little with a grinder (threads on it are correct, but the lower body is to large to fit into the injector hole as it comes in the kit).

I say check you timing first to make yourself feel better (its free to do anyway), then do a compression test.
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The Uppity 12v Admin
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While the logic of a timing slip isn't quite there, it fits the symptoms more closely than a head gasket issue. If his truck was running that poorly due to compression loss, he wouldn't be able to keep coolant in the engine. Unless it was leaking between like all the cylinders, which I suppose is possible but very unlikely based on what I've seen.
 

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While the logic of a timing slip isn't quite there, it fits the symptoms more closely than a head gasket issue. If his truck was running that poorly due to compression loss, he wouldn't be able to keep coolant in the engine. Unless it was leaking between like all the cylinders, which I suppose is possible but very unlikely based on what I've seen.
The truck I pulled this head gasket off of ran, drove and held coolant pressure. It white smoked (just like the OP described), so I went through all the trouble of checking the timing and replacing the injectors before I finally broke down and did a compression check.

Sure check the timing first (free and relativity easy), but if that isn't it, I'd bet its a compression issue.

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Discussion Starter #7
Thank you all for your input. I did not mess with the timing with the head off, but it was recently adjusted about a month and a half ago.

As far as injectors go, they aren't new, they are the same ones in it had had previously to the fix. I cleaned them by soaking the tips in some diesel fuel additive (I had no diesel fuel laying around) and then very carefully cleaned the excess soot off the tips making sure not to damage the tips or get anything in the spray holes to clog them.

As far as head gasket problems, the head gasket it has in it has about 2 miles on it....maybe I should measure in terms of minutes instead. The truck has been run for 30 minutes since the fix and that has been mainly idling with some light driving around the block when I discovered the problem. Would this blow out the gasket like in your picture?

Could setting the valves incorrectly or poorly have something to do with it too?

When I was turning the engine over by hand could I have messed up the timing? I turned it back and forth quite a bit with the head off (don't worry I did oil the cylinder walls) to get TDC and make sure I was there, but I could still be wrong. What about it revving to around 1200 rpm when I first cranked it (my foot was on the pedal getting it to start because of air in fuel lines). It was just a short blip.

I just started it yesterday to move off of the driveway and it started pretty hard...it was 85* out...

Again thank you for the input and guidance. Still thinking timing? It has almost all the symptoms from the research I have done, but I don't know how it would have slipped, maybe from me turning it back and forth?
 

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Could setting the valves incorrectly or poorly have something to do with it too?
If the valves were not adjusted properly and one (or more) was being held open, then yes, that could be a cause of low compression which would result in un-burnt fuel/ white smoke.

Did you lash the valves after re-installing the head??
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Discussion Starter #9 (Edited)
If the valves were not adjust properly and one (or more) was being held open, then yes, that could be a cause of low compression which would result in un-burnt fuel/ white smoke.

Did you lash the valves after re-installing the head??
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I did lash the valves after re-installing the head, but, that would have been my first time. When I re-lashed them again in an attempt to resolve the symptoms I'm having, that was my second....so that's why I have my doubts. I am having someone with the title of "Diesel Mechanic" look at it in a few days just to cover my rear, but that certainly could be the issue too. I am pretty handy when it comes to fixing things and putting them back together, but when it comes to the small details like using a feeler gauge, I lack experience, so I need some backup.

I plan on having this mechanic check valves and check timing hoping that one of those are the issue. If not, well then I'm at a loss. I guess I would start with a compression test and go from there as I don't want to spend $600 on injectors I may not need.

That leads me to another side question. How big of a deal is it to replace one injector at a time versus the whole set. I've always heard you should do them all. Is that correct?
 

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The Uppity 12v Admin
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Misadjusted valves can absolutely cause a low compression condition which would explain what's going on. However, timing is most likely to slip when recently disturbed. Most often on the first startup but I've seen it happen when trying to purge the lines of air as well.

The issue I have with blaming the gasket is head gasket failures between cylinders is that that's a failure that takes a lot of sustained load to develop. It's something you see on the 370hp marine engines once they have several thousand hours, which generally run at moderate to high sustained loads, often for dozens of hours continuously. Given what you said about the previous owner of the truck that happened to, it doesn't surprise me much. It does surprise me that it would happen on first startup with a fresh gasket. Improper surface cleaning or assembly can always cause problems, but composite gaskets are normally very forgiving on these engines with regard to surface conditions. I suppose the gasket itself could also have been defective to begin with.

My point is don't pull the head right back off. It's more likely it's not the gasket itself, and both slipped timing and low compression from misadjusted valves will show similar symptoms. If the PO is admitting a lack of confidence with his overhead set, that's a great place to start double-checking.
 

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Discussion Starter #11
Misadjusted valves can absolutely cause a low compression condition which would explain what's going on. However, timing is most likely to slip when recently disturbed. Most often on the first startup but I've seen it happen when trying to purge the lines of air as well.

The issue I have with blaming the gasket is head gasket failures between cylinders is that that's a failure that takes a lot of sustained load to develop. It's something you see on the 370hp marine engines once they have several thousand hours, which generally run at moderate to high sustained loads, often for dozens of hours continuously. Given what you said about the previous owner of the truck that happened to, it doesn't surprise me much. It does surprise me that it would happen on first startup with a fresh gasket. Improper surface cleaning or assembly can always cause problems, but composite gaskets are normally very forgiving on these engines with regard to surface conditions. I suppose the gasket itself could also have been defective to begin with.

My point is don't pull the head right back off. It's more likely it's not the gasket itself, and both slipped timing and low compression from misadjusted valves will show similar symptoms. If the PO is admitting a lack of confidence with his overhead set, that's a great place to start double-checking.
I was definitely trying to purge the lines of air so that could be the issue.

I may not be 100% confident in my valve lashing abilities, but I am confident in my cleaning of the surfaces. Those suckers were spotless, so I really hope that isn't the issue otherwise I really need to start questioning my "handiness."

The guy I have looking at it in a few days to do valves and timing is a very sharp dude and has been doing it for years, so I think his experience tops mine 😉

THANK YOU all for your input, help, and guidance. It is so nice knowing there is such a great forum to post questions to and get a plethora of accurate (mostly) answers in a very short amount of time.
If you have any other input or advice, please don't hesitate to let me hear it.
Thank you.
 

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Be sure to post what the eventual solution is, many of us here would love to learn what it turns out to be.
 

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No updates yet. I will be sure to post the update with the issue. It is being looked at towards the end of this week. As soon as the issue gets resolved 🤞 I will update the thread with what the problem was.
 

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Well I got the results back. Sorry it took so long, but the shop I took it to was very backed up and "swamped," so it took a little longer to get to.

Timing nor valves were the issue, both were set correctly.

The issue was a couple of bad/gummed up injectors. The thump/knock I was hearing was a fuel knock. Apparently during the head gasket replacement process I must have gotten the tips dirty or something because the mechanic said he did a pop test on both of them and the spray was off along with #3 not holding pressure. It started to leak around 800psi.He cleaned up those injectors, re-shimmed them and it runs great. Barely any white smoke at all. He said he sort of worried about overfueling the #3 cylinder because of the injector being stuck open, but said the amount I drove it (barely 5 miles to the shop and it didn't get up to operating temp) wasn't horrible.

I'm trying to think of everything he told me, but I think that was it. Sorry for the long wait on this response. I just got the truck back today.
 
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