I've been searching around for similar posts and found good advice on injectors, overflow valves, lift pumps, etc. but I'm still unsure of my issue quite yet.

I started having a clacking/knocking noise at idle and higher under light throttle which gets quieter after warming up. It's louder when cold and almost not there when warm. It started right after I adjusted the valves and changed the oil to full synthetic 5w40 Mobil One(for newer diesels I guess). It sounds to me like it's coming from cyl 5 or 6, but not from the valvecover area. I hear it more underneath the truck and either driver or passenger side.

Ive suspected the oil being too thin and plan on going back to plain ol Rotella 15-40 that the truck has been on all of it's life before now, but I'm wondering if I could have gotten the valves a hair too tight on #5 or 6. I do remember #5 or 6 being hard to tell how tight it was and moving the rocker back and forth on the shaft to get it in the perfect "loosest" spot was a lot harder to do than all of the others. They were all very loose and needed to be done(100k? maybe). I have tried loosening each injector line and each make it miss while I can't tell that the noise goes away.

Another symptom is vibration of the truck that feels like a weak cyl. Under a throttle stab or load, the vibe is not there. The noise doesn't seem to be there under a throttle stab, but maybe some under load driving.

Now, knowing the overflow valve has never been changed on my truck, nor has the lift pump and low rpm I've been encountering only when cold, I've been wondering if it could be an overflow valve symptom.

So, basic question would be can the valves on a cyl being a tad tight cause the noise or "miss"? What would be a symptom of the valves being tight? I'm skeptical about the oil, but what's your opinion?

I've always heard the "normal" lift pump pulse/tick in the exhaust on this truck and though it bothers me, that's not the noise. The noise is also not coming from the trans or flexplate. I'll also add that it's not 100% constant and intensity changes some from one revolution to another.

Long winded I know, but I'm trying to be thorough. If anyone can give any advice on diag, I'd appreciate it.

 

There was a person either here or on another CTD board I frequent who said switching to synthetic caused him a noisy engine.
Switching back to dino oil cured it.
Personally that's where I would start.

 

Im with Bill here i wudnt recommend running anything thinner than a 10W in a 12 valve and I'd only use that in extreme cold. Do you notice any difference in oil psi?

 

If the noise coincides with the change in oil, I'd try that first. It is also the cheapest place to start.

 

I haven't noticed any oil pressure difference, but the stock gauge is lacking in its abilities. The sending unit is new though, so it's better than it used to be, but I can't tell a difference warm or cold. *Edit* I can't tell a difference between synthetic and Dino oil. I can tell a difference between hot and cold pressures on the gauge with each oil.

It gives me hope that others have mentioned something before about synthetics. I will be changing soon. We'll see how it acts after.

Thanks for the replies guys!

 

Double check those back two sets of valves. Easy to do. It's also easy to pull a pushrod out of the lifter cup when messing around back there. Buddy did that and bent a pushrod. Had a clatter noise and weak cylinder vibration...

 

I hope I didn't bend a pushrod. I didn't mess with any of the pushrods or loosen the rockers any, just the locknut on the rockers and wiggled the rockers as I was tightening them so they would be in the "loosest" spot for the feeler gauge. If the rocker is too far to one side ot the other, it gives a false tight reading and binds the feeler, but in the middle, the feeler will slide free. The back two were a pain to do though and always read tight. Will too tight make noise? I figure too loose will, but I think I may have them a hair tight rather than too loose. They are definately tighter than they were.

Since the noise and vibe started after the valve adjustment and oil change, I guess I'll check the valves again since it won't cost anything to make sure.

 

Checked and adjusted the valves again as perfect as I could. None were more than .002" out. Now they might have a couple at .001" out at most. None were too tight. I checked all six cyls. I can't get them any more perfect than they are.

After that, I cranked it up and thought it sounded better, then heard it again. I was thinking it might not have been as bad or maybe I was just wishing it was better, so I decided to change the oil back to 'ol faithful Rotella 15w40.

Now it definately sounds better and even feels like it runs better when cold and warm. Ive noticed it smoking at idle when cold, which looks a little like oil smoke, but smells like diesel to me, so I can't tell, but I'm not worried.

Overall I'm happy, though it's not "perfect" and still there, just muted and not as noticeable. Maybe I'll get around to checking fuel pressure next and see how the 305k mile lift pump and overflow valve are doing.

Thanks guys.