Hey folks. Picked up an XJ today for a decent price but it's got a knock coming from the bottom end that increases with engine speed. I'm really hoping it turns out to be the TC bolts (please baby jesus) but im preparing myself for it being rod knock. The oil pressure is pretty low at idle (between 10-20psi) when warmed up but is pretty decent under load.

The jeep has around 215K miles on it though.

What I'm wondering is if I do need to rebuild the bottom end of this thing...how likely is it that the crank needs to be sent off to the machine shop? I'd prefer to just do a basic bottom end rebuild with the engine still in the jeep.

 

Got more indepth with it this afternoon. No knock when its cold and good oil pressure. At operating temperature the knock is very obvious and oil pressure is under 20 at idle and around 30 under load. But when cold its at 40psi. Safe to assume bearings?

 

Just went out and unhooked the injectors 1 by 1. instead of the knocking going away it just got much worse no matter which cylinder i cut fuel off to.

Anyone?

 

Don't have much to say but I do know that the 4.0L oil pressures when hot are around 10-13 psi idle and 40-55 under load

 

Collapsed lifter? What year is it? I believe some of the newer ones had problems with pistons breaking. Don't hold me to that tho.

 

Well take a listen here. I had it baking hot, then it sat 1/2 hr in 30* weather, then the camera mike....Normally you would hardly notice it. It's been there since at least 02, about 150K ago. I've been thinking of checking crank end play some day.

 

My oil pressure runs at 60-70 constantly

 

That's a substantial range....10 is on the low side, 20 is super.
I'd agree that a bottom end knock when the engine warms is probably bearings. Only way to tell is to drop the oil pan and check them. Plastigage works well.
You can eyeball the crank journals too, but I bet they're fine.
Piston skirt cracks are another somewhat common problem, but that noise tends to lessen as the motor warms. Still wouldn't hurt to give them a peek from underneath while you're in there.

 

Alright thanks guys. I'm gonna check everything out this weekend and drop the pan. Worse case...I've found a used engine within 20 miles of me with only 83K on it for 600 bucks. Would probably be a better route to go than to put 400-500 into a basic rebuild of the bottom end of a 215K engine.

 

Mine sounds the exact same

 

Mine sounds like that as well. Sounded like that when I bought it and almost 2 years later of it being a daily driver it still sound the exact same. I too one day will check things out but until I need to drop the pan for other reasons I will just let it be. I did check the converter bolts and flexed the flex plate to see if I had any cracks but not such luck.

Max

 

Hah you guys are ballsy. I just can't bring myself to drive around knowing that the bottom end could give at any time. Plus I'm going to be using this as a DD and getting rid of my other car (sick of car payments).

 

Could be a lot of things, the 4.0L I6 is a noisy engine to begin with.


Do you have an auto trans? If so check the flex-plate to make sure the bolts are tight and it isn't cracked (a loose/cracked flex-plate is known to sound a lot like a rod knock.).


If the flex-plate is ok the next step would probably be to drop the pan, a bad bearing or cracked piston skirt should be evident with the pan off.


Bad lifters or Piston-Slap (Piston-Slap is annoying but generally harmless) could also be the cause.

 

I've read up on these issues to some extent. I ruled out the flexplate thing considering the knock gets much louder when I remove fuel from any of the cylinders. I don't know if piston slap would be affected by that.

I do know however that when I went to see the jeep it was a few quarts low and had horrible oil pressure. Adding oil helped with the oil pressure but not the knock.

 

Running low on oil definitely increases the possibility of internal engine damage (especially to bearings), cam/lifters could be affected as well. Knowing it was run low on oil I would definitely pull the pan and check the bearings.