Bad wrist pin/bushing, maybe?
 

I've still got a pretty pronounced camshaft-speed knock from cylinder #8. I've replaced the injector, and there was no improvement; it may have actually gotten a little worse. It's worst when cold, and quiets a little bit as it warms up. Classic fuel cackle does the opposite, so it seems to rule that out as a cause. When I shut off the #8 injector, I hear no knock at all. It doesn't sound like a rod bearing to me, but it is a possibility. I did change the oil yesterday, and there was no improvement at all. A sample of the drained oil is on its way to the lab for analysis . . .

It will occasionally quiet down for a short period of time, to the point that if I didn't know it was knocking I probably wouldn't notice it. This is the reason I'm leaning toward it being a wrist pin causing the knock. With floating wrist pins, I'm thinking maybe the pin is worn unevenly and sometimes rotates to a point where the clearances are closer to spec, and it quiets down temporarily.

Does it seem plausible, or am I way off base with this one? I'm still going to try to rule everything else out before I pull an engine that's only been in the truck for 2,700 miles, but I've got a sinking feeling here. I'll hook up the breakout box and try to get some audio/video posted later today.

Here's the audio. This seemed to be the best place to capture it without too much background noise from the fan, injectors, etc., but it actually sounds worse standing there than it does in the clip. It should be pretty obvious when #8 is cut off and turned back on.

Oil analysis asap.
If its the rotating assembly there should be an indication of wear metals in the report.

It's on it's way to Blackstone now; should be there Monday according to USPS. If it looks normal, I guess it's time to swap the injector out of #8 into another cylinder to see if the knock follows, but I really don't think that's the problem. I'll get the stethoscope out tomorrow and see what I can hear. I put a mechanical oil pressure gauge on it a little while ago and it looks good. 42 at idle, and 60 at 2,000 RPM.

EDIT: The pin bushings are bronze, right? If that's the case I should see elevated copper, tin and possibly arsenic levels, I'd imagine.

Sounds more valve train to me. Dead lifter, bent push rod, etc. Maybe the cyclical nature of it is related to the rotation of the lifter. Lot easier to check that than the wrist pin too.

I'd love for it to be that easy, but I didn't notice any difference in the noise with the valve cover off. I have to retorque the injector, so I'll check again and see if I missed anything. I know how my luck runs though, lol.

Chris, just a thought, but there's probably no accurate way to measure the stroke with the head on and the engine installed, is there? I'm just kind of wondering if I could get an idea of what's going on by seeing if the stroke is shortened at all due to slop in the bearing or pin.

Maybe a long thin screwdriver or rod dropped thru a GP hole to rest on top of the piston, observe the end of it then rotate the crank back and forth. If there's slop in the wrist pin I would think the piston would not move immediately as the slop is taken up with change of direction. Compare to another cylinder. Just spitballin.

I thought about that, but I'm not sure I'd be able to tell that way. It could be a matter of only a thousandth or two of an inch causing this mess, depending where the issue actually is.

I think I might start tearing down my old engine this week in preparation for the "event". Maybe I can toss a head gasket in it and just run it with the low compression in one cylinder while I get this one taken care of. Kinda glad I didn't sell the old one to a rebuilder now . . .

If your sure its number 8 switch the injector to #2 and see what happens. Easy and will confirm. I had a noise like that and it was the injector. Only injector I ever changed, and it was #8, in my E99. I also put Clays FRCO on, but it worked for me. I hope its not your engine.

It's definitely #8. When I kill that cylinder with the breakout box, the knock disappears. I'm going to swap the injector to another cylinder, but it's a fresh injector I installed last week and it was making the same noise before I installed it. I was really hoping it was the injector, but the chance of it being 2 in a row is pretty slim.

With injector swapping I was thinking perdels may give us a clue here but on #8 they can be all over the place and just muddy the water.

Anyway to confirm no air or fuel pressure problem?

Fuel pressure is 52 at WOT, post filter. Haven't pulled the test port on the head and checked it there yet; I'm kind of in a holding pattern until the oil analysis results hit my inbox . . .

From the video, the sound seems too light for a rod bearing. You may be right about wrist pin, but could you use your stethoscope on the valve train (with valve covers removed) to see if there is anything there? Noises are hard to pin down sometimes. Did you assemble the motor yourself and mike the pins? Are the pistons new? A sticky valve would cause a miss wouldn't it?

The engine was a salvage yard pull that had 87k on the odometer. Compression was quite good on it; I checked that before buying it. If the oil analysis comes back good, I'm going to start poking the stethoscope around and see if I can figure anything out. It doesn't have a miss; I was intentionally shutting off the #8 injector in the video. I know I have some injectors with worn poppets (#8 isn't one of them), but I'm not sinking money into more injectors until I figure out what exactly is going on :(