Knock goes away when I shut off cylinder. Problem is??

[Rob4]

I noticed a slight knock from an engine I recently installed. It's a military surplus 2002 AMG 6.5. I was told it was good and had less than 40,000 miles. It's very clean inside and out and seems to run great aside from this knock which doesn't belong. The knock wasn't very noticeable at first but after about 40 miles I noticed the knock inside the truck and it sounded like it was coming from the passenger side down low by the heater. Then I could hear it mixed in with the usual diesel engine noise. The knock increases/decreases with engine speed. Using the GMTD Scan Tech software to shut off cylinders caused the knock to decrease almost completely at #2 cylinder. Just listening to it I would have thought #6 or #8. I replaced the #2 injector but the knock was still there. I pulled the pan and checked all the rod bearings and all are in good shape. The rod bearings Plastigaged at less then .002. What next? Since the noise mostly stopped when fuel was shut off to #2 wouldn't that eliminate a valve train problem?
Any help would be greatly appreciated.

[john8662]

Have you checked for injection lines touching, suspect anything near that cylinder you're checking.

You already got to what I would have originally suspected, rod bearing. Usually if it's a front cylinder it's due to a bearing failure, last in the oil circuit. Anyways, you really need to pull a compression test now, there is really no telling beyond tearing it down what is the cause.

[Lightyear]

I had a odd knocking, almost 'clanging' metallic sound coming from the right hand bank of my old 6.2. Using a stethoscope, I pretty much narrowed it down to #4. My thoughts were a rocker going bad somehow. Don't know, as I sold it before digging in, but maybe pull the valve cover and check the condition of the rocker arms and shafts. It'll take some time and greasy labor, but is also a cheap way to rule out another cause.

Good luck...

[Robyn]

Any time there is a harsh metalic clanking from the RH side try placing a gloved hand on the turbo's metal heatshield that covers the rear of the turbo.

This shield will act like a real echo can and will make a lot of noise.

A knock that is more hard could be a wrist pin.


Keep is posted

Robyn

[oldmechanic]

could also be scored piston\cyl wall or cracked piston skirt
OM

[Robyn]

If turning off a particular hole stops the noise I would try swapping the injector to a hole on the other side of the engine and see if the noise follows before I got to froggy with the tools.

Missy

[Rob4]

Thanks for all the input. I've looked the best I can from underneath looking at the bottom of the pistons for damage but can't see anthing wrong. I will do a compression check and see if anything shows up. I will get back to everybody when I find out something. Thanks.

[Warren96]

This is the second time that I have read this topic, and I just noticed that no one has mentioned the famous aluminum heater line resting on an injector line causing a knock. I just bent mine away from each other.