97 4.0 knock popped up out of no where.


So one morning engine had a terrible knock.
Out of nowhere really. Never heard it before. 266.6k miles on it. Man trans.
I tried the mystery oil no avail.
What I finally learned is that the rear main seal has been leaking. Enough over time to drain my capacity down 2.5 qts before I found this problem. Anywho. Gonna drop oil pan and hopefully won’t find a skirt there. No metal in last oil change or sign of any.
My guess is it’s rod bearing. Def #1 cylinder with stethoscope. And I did replace rockers and push rods. Plenty of oil on all of them after filling it back up to spec. More performance but did nothing for knock.
Any thoughts ?
I’ll know for sure in a week or so when I drop the pan. Ugh. Cant post a video that I have but knock mostly disappears above 1800rpm.

And when hot at idle it’s noticeable but not loud.

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Burnt valve?
Exhaust leak sometimes sounds like a knock.
Intake leak one cylinder lean.
Gummed up rings/ blow by

Never look down on anyone unless you are helping them up - Jesse Jackson
It’s possible. After watching numerous vids I’m going with either piston skirt issue or rod bearing. It is only #1 cyl with this issue which is common.
I plan on rod bearings in any case but if it is a piston issue then I’ll replace all six in-engine. Ugh.
There was an TsB issued in the 90s about 4.0 having piston slap due to carbon buildup on top of piston hitting the head. More for the pre 97 engines but interesting nonetheless. I’m glad it’s not electrical issues. I cant see electricity and I suck at chasing electrons .

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Good luck dropping that pan, it was a pain on my 2005. I had to remove the two cats in order to drop the exhaust pipe down enough. Hopefully that won't be the case for yours.

Are you going to do the rear main seal while you have the pan out? The seal itself is cheap enough.

Take some photos if you get a chance.
will def be replacing rms !! Since this is a pre '99, this doesnt have the dual cats they used in 2000+ models.

I only have one cross pipe from exhaust..... I watched a bunch of vids, mostly for 2000+ and i wouldnt wish that on anyone.
My wife's cherokee had a knock that i thought was bearings. Turns out the torque converter had a bolt back out and it was hitting a piece inside the bellhousing