LDT 465 1C engine noise

I have what sounds like an upper engine noise, but I am not sure. It is a 1983 Air Force M35A2C That has not had the truck or engine rebuilt as far as I can tell.
It shows 11500 miles and 375 hours I don't know if this is actual or not. To give you the history that I know I bought this truck nonrunning from someone who had two of them.They removed some parts from the one I bought to get the other one going. I was told they swapped the electric fuel pump and that was all it needed to run.
Actually they swapped the pump, took the brakes and wheel cylinders from two wheels. It also was missing a bed and two rims and tires.I bought it knowing all this and
the risk involved with buying a non running truck. What I have done to this point is new fuel pump ,cleaned fuel tank, changed fuel filters,new air filter and two injector pumps, it did not run right with the first one I put on. I am in the process of A3 brake swapp and trying to find the source of the enging noise.I have tried to convence
myself I will deal with the noise later ,but it bothers me knowing it is there and I can't seem to get my mind off of it.The truck starts better than any vehicle I have and runs good and strong. It just sounds like it has a valve way out of adjustment. I have adjusted the valves they were fine and I have pulled all the injectors. I did not see anything that looked bad. I have listened all over the engine with metal rods, screwdrivers, wooden dowels and can not pinpoint the noise. I also pulled the flywheel inspection cover and did not see anything there. On the passenger side of the engine at number 6 there is a small amount of oil sepage from the head gasket and you can see the oil move a little while it is running ,but you can not feel any air comming out. I have felt for exhaust leak and did not find any. I have searched this site for common problems like this and was not able to come with much there. I am to the point of pulling the oil pan and heads to look inside. I have a few short videos and maybe someone can point me in a direction I have not thought about. I have a rebuilt in 1974 LD 465 that has a LDS 465 turbo on it that I pulled from a
parts truck. I dont want to use this engine unless I have to I would like to fix the other one as it is a TD block.
Thanks Jim

https://www.youtube.com/watch?v=1nTzXPHDNlg

https://www.youtube.com/watch?v=pCx4aTlgf9o

Could it possibly be coming from the air compressor? I don't hear anything odd. Maybe I have a deaf ear to it. I try not to hear bad noises from my diesels....usually means money.

It sounds like it is comming from the back of the engine last three cylinders. The video sounds different than when you are standing by it. It does sound somewhat normal on the video.
Here is another one from under the truck. Maybe I am being paranoid I just do not want to damage the engine beyond repair.

https://www.youtube.com/watch?v=wrW_hEY2wwY

Yea, I hear it. One of these guru's will chime in eventually.

Sounds like a rocker arm to me. I would hold all of them to find the one that clicks in time and see if holding one way of the other makes the noise change.

I have held them also took a piece of wood and pushed down on the top of the rocker while running.
There was no change in the noise. I agree that is what it sounds like and I a hope it is something that
easy.

Sounds like mine thought that was normal , curious to see what you find out

Mine has the same tick or knock too . I have been nervous about it. I can't identify the source either.

You've put the "stethoscope" to each of the injectors?

I'd say the next step is to drop the oilpan and wiggle stuff.

I have listened to each injector they all have a different sound, but I could not relate it to the engine knock.I have also cracked the line at each injector while running and the noise never changed but the engine ran rough with each one I cracked loose. Now I hate to even mention this because it even sounds stupid to me but I have also listened to the injector lines also. Number 4 injector line has a knocking sound that seems to be the same frequency or in sync with the engine noise. I have changed this injector with one from a different engine it made no difference. Something else I have noticed when I first start it after it has sat overnight I don't here the noise until about the time the oil pressure starts to show on the guage 15 - 20 seconds. It has good oil pressure 65 psi cold 35 psi hot. At 1200 rpm I can't here it, but it may be from the turbo screaming I am not sure. It does not get louder with more RPM or load.

The knock that my engine makes doesn't get louder either. It's definitely in sync with the rpm. I'm not sure if it's every rpm or every other rpm. The strange thing is that I have had the engine running in front of many people who are gear heads and not one of them have ever mentioned the knock. I hear it loud and clear. Maybe I hear it because I have an emotional attachment to the big dumb truck.

Maybe this is a camshaft problem?.

You may have a small hole in a piston, not big enough to make it miss, but enough to hear the tick from compression escaping. Does it have any blowby from the slobber tube when it is running cold?

I started it cold and it has a little blow by
I could not see it if I put my hand over the
end I can feel it. When it is warm/hot
I can see the blow by. I don't know what
is normal or excessive. I does not seem excessive
to me ,but I have only been playing with big diesels
for a few years now so not a lot of experience
to go on.

thinking this over Do not remove a push rod/s. to test. singly or otherwise.As back pressure, (as in a JAKE BRAKE) could hold a valve open. also pressures and vacuum might be too high.

Would it run or damage something running
without a valve opening and closing?
if not it would be worth a try.

Jacklegjim, you mentioned that you don't hear the knock until the oil pressure builds up. Could the problem be the oil pump? After I get my transmission back in my truck I will start the engine and listen for the knock, paying attention to the oil pressure. Probably won't be until Saturday.

The noise may not have anything to do with the oil pressure
,but there does seem to be a delay in the noise on a cold start.

If the noise doesn't get louder with an increase in rpm, that leads me to believe that it's coming from something that is always under the same load.

Use the camera you filmed with, and holding it firmly (or fix it) so that a clear LONG video of ALL the push rods and tappets can viewed at once and "TIMED" to sync that tapping sound. The problem has to be at the top end somewhere. lets work it out. ( you could place a finger on each rocker and try to sync the noise with the culprit after you film and post).
I tried to judge but the film is too fast panning, but seemed to think number 6 from front?