It's not the flexplate, it's not the timing chain...
 

2001 XJ, 4.0L

Since I've owned the Jeep I've had some sort of engine noise, and can't seem to pinpoint it. From all the posts here and videos I've seen I've heard explanations of rod knock, timing chain, flexplate bolts, piston slap, rod bearings, lifters, push rods... I'm sure there's more.

I just replaced my rear main seal and while I was down there I could see my timing chain had a fair amount of play in it so I replaced it. I also removed, cleaned and tightened my flexplate bolts and inspected my flexplate for cracks. All looked good. I even checked all the rods for play and they all seemed good. (Rod bearings have about 4K miles on them.)

I got it all back together and on startup it sounded as if the knocking actually stopped, but it came back almost immediately. Arguably louder than before. When I accelerate, even slightly, the knocking goes away. It's just at idle that the noise is quite loud.

So my question is... what could it be. I'm starting to think push rods and/or lifters?

Fresh oil change: Royal Purple 10W-30, Bosh filter.

Thanks in advance for the help.

The 4.0 is a very noisy engine that was designed about fifty years ago. As long as you have good oil pressure, runs well, and you're able to turn the radio up you will be fine. It's not an over head cam Toyota engine, or an engine with roller lifters.

Get a stethoscope and start listing around engine to narrow it down. You can use a large screwdriver too with handle pressed up to your ear and tip touch around suspected areas until noise is loudest or rathrhythm is the same as noise you are describing. Check your motor mounts...

It was the fact that the noise went away when I first started it up, then that the noise goes away on acceleration that leads me to believe there's something to "fix" with the sound. Perhaps something that is effected with a higher oil flow rate that quiets it down.

Motor mounts look good, I checked them. I've tried to pinpoint the sound just not with a stethoscope or using the screwdriver method. It's quite misleading just hovering over the engine as I have been. I feel like I pinpoint the source everywhere I look.