another guy with a tapping 871

[dhirocz]

I figured I should start my own thread. This noise is starting to worry me.

871, 770k miles, 21k hours. @m*m^2 @ 685 k, bypass filter, regular oil changes with gear oil since I got it at 505k. At or around 685k, it got a bearing roll, 6 dimes in the oil pump, new compressor, damper, 2 new injectors, jake springs, overhead has been set twice, a new valve cam, and some other parts.

I suspected my compressor, and at first it only made noise under torque and it seemed worse when it was working. Now, it makes it more under torque, but I can make it make noise at 1000 rpm while stopped, too, even with the compressor unloaded. It does NOT make noise while jaking.

I can say this:
-oil pressure hasn't changed. It's 16-18 while idling, 42-44 while driving depending on RPM.
-engine is not running as smooth as it used to.
-no smoke, no coolant loss, no change in fuel consumption.

I'm 3k miles shy of my next oil change, but I'm considering doing it early and cutting open the filter to check for metal particles. I have a filtermag on the full flow.

It sounds like a case of excessive piston slap to me, but before passing judgement, I figured I have some things to rule out:

- injector check.
- run the engine and see if I can visually see the cause of a noise under the valve cover with it off.
- check the front geartrain for any obvious damage.
- check cam timing.
- check the air compressor for knocking with a stethoscope.
- check the oil filter for metal.
- finally, check the block with the stethoscope for noise from a worn cylinder.

This leaves me with a couple questions:

I can check for a leaking injector, no problem, but what about an over fueling or otherwise failing injector causing a knock?

If everything else checks out, how common is it that a cylinder wears like this? The noise has gotten progressively worse over the last couple of weeks.

I don't drive far, nowadays half of my miles are unloaded, and it hasn't seen mountains or even over 10 lbs of boost in at least 4 months.

I do have a new Cummins damper I was holding onto for my inframe...mine was already replaced, but it's one of those vibratech TVD dampers, not a Cummins. Maybe it's a good idea to throw the OEM on there early even though the TVD is not that old?

Input is appreciated!