I have a 1990 Cherokee my 4.0 has some kind of knock that I can not find! I've changed out my main &a rod bearings. Comes up after the oil starts warming up . I can't figure this out. Pulled the tranny replaced torque converter checked the fly wheel for cracks all good there. What else could it possibly be!!!!!!

 

Could be lifters, pistons, or maybe a cracked exhaust manifold. Or none of the above. Did it do it before replacing the main and rod bearings? How is the oil pressure?

Do you have a stethoscope? Listen to the oil pan and the valve cover, in a couple different places, including the bell housing. And the block near the spark plugs, even. Everywhere. You may find something on Youtube that sounds similar. But you will still need a stethoscope to find out exactly where it is coming from.

 

mine does it cold, piston slap they tell me??

 

Piston slap typically happens on cold start up and decreases as the engine comes up to temp. Slight rod knock usually will become audible as the engine approaches running temp. Bad rod knock happens all the time cold or hot.

Try and narrow it down with a stethoscope. Is it louder in cab, in the engine bay. Back of motor or front. Passenger or driver side.

What did your old bearings look like? Hopefully you labled what cyl they came from.

 

My 90 has, and has had a consistent knock for over 100K, (at 280K now). For lack of a better idea I'm wondering about crank end play. What knock, actually since at about 135K, wouldn't have worsened and blown something? Idk, I just live with it. It is on U-Tube btw.

 

How old is the water pump? Ive had two of them with worn bearings that never leaked but made some horrible knocking. The first one actually had me worried. It's not so obvious where the sound is coming from either. The second one I knew right away as its not as bad and was familiar.

 

Sound is coming from the center of the block I'm thinking piston slap

 

And yes the sound was there before I replaced the bearings. Checked all the lifters they seem nice and tight

 

I'd about bet you my Sweetish vacuum motor collection it sounds like this here>

 

Yes that is exactly what it sounds like. Driving me nuts

 

Mine has a terrible knock in it also (it had when I bought it) No knock until it is under load. Power is good and is only happening at about 4k rpm, My son in-law told me when I was looking at getting the XJ that this is a comin knock with the 4.0 often caused by a loose oil sending unit (rod rattle). I have had my XJ for 3 years or so and the only thing that really worries my is if it stops making that knock.

 

just listen to the video posted that sounds like a water pump going out to me, nothing like the noise mine has