Jeep 4.0L - PYB 10w-30 (first UOA)

[jeepman3071]

Not broken, just gunked up. Its extremely common with 4.0 engines to have gunked up lifters that tap and make noise. Running higher RPM frees them up a bit. I'd say just keep running the PYB and don't be afraid to rev it. The only quiet 4.0 I've heard is my buddy's 2000 XJ. It had PYB 10w30 every 3k miles its whole life verified by the previous owner's receipts from Jiffy Lube left in the glove box. Pulled the valve cover and it looked spotless inside. I have a pic of it floating around this site somewhere. I think almost all of them have a little gunk inside and that is what makes the lifter tap.

The piston skirt issues aren't from high revs, it is a casting issue just like the 0331 head. The skirt with either crack and break or it won't.

 

[SwampSurvivor]

The valvetrain looks spotless - no sludge or varnish on it.

I can't remember exactly, but I'm at about 4500 on this run of Pennzoil Conventional. In the spring I'll do a change and try the higher stationary RPM trick ... after the engine comes up to temperature.

I figured the chatter was a broken piston skirt ... but that wouldn't have gone away. If anything, it would have likely grenaded if it was a broken skirt.