I’m a proud owner of a 96 Cherokee with the 4.0. I picked it up for 1000 bucks from a good buddy of mine who didn’t have the time for it. It’s got typical floor rot, but other than that this Cherokee is in GREAT shape. I had the motor swapped recently because the original engine ended up with a severely broken piston skirt. Now this new engine I put in claims to have just over 100k miles on it happens to have a lot of racket. Most concerning is what I would call a knock. Is more distinct on cold starts and quiets up almost to a normal sounding engine when it’s warm. Almost sounds like a diesel, warm. I know my old engine before the piston skirt began to break was a nice quiet engine. But this “new” one makes so much noise it’s stressing me out lol. None of it sounds major what so ever, it runs excellent. It’s just small ticks and that one faint knock that worries me. I’m no Jeep expert, at least not yet. This is my first Jeep. I guess what I’m wondering is, can these old Jeep 4.0s really make a lot of unknown racket? And what possible things could be going wrong for me to have this faint knock? Like I said it’s not over bearing. It’s just much more distant cold than warm. Do slog of 4.0s have this faint knock? I’d appreciate and feedback. The more I learn about these the better. I’ve always wanted one so I’d like to know all I can. Especially with this “new” engine stressing me out. Don’t want have to change the engine again lol.

 

They should not be noisy, try an engine stethoscope

possible other causes, torque convertor bolts loose (check and tighten, examine for cracks)

exhaust manifold cracked

 

I figure with the motor being changed by a trusted family mechanic, the torque converter bolts wouldn’t be the issue. It was actually just changed about three weeks ago. I do plan to use a stethoscope tho. I’d also imagine the mechanic would’ve noticed a crack exhaust manifold. I’m really just worried it’s another bad piston skirt it just isn’t that bad yet. Other than broken piston skirts, do you know what else the 4.0s are known for?

 

Rod knock, failed lifters, damaged pushrods

 

Mine is noisy on cold starts, but quiets down once warm. After, it sounds great, especially after a long ride, I open the hood, rev it up, and listen.

If you are worried, do a compression test, get an oil analysis.

I think I read somewhere here that the cold start noise is piston slap. But once the pistons warm up and expand a little, the slap goes away.

But like awg, says, check the other things with a stethoscope.

 

I’ve been doing quite a bit of research both more on here and elsewhere on the web. Watched videos and read some info on the whole thing. I’m pretty confident I have piston slap. Which really irritates me bc I just had this engine put in a few weeks ago. I guess that’s the price you pay when buying a used engine. I’d say I definitely have a mild case compared to some but idk how long this engine will last like this. I don’t have the means of replacing the pistons myself nor do I want to put another engine in. I’ve always wanted a cherokee but this first experience isn’t going well. Starting to think these are junk because of all the videos I’ve seen and things I’ve read. I’m not real sure what to do now. I’d hate to get rid of it, I really love this Jeep. Super fun to drive but I’m not sure what I can do that isn’t gonna cost me another fortune. Is there something I can do to quiet the knocking down? Maybe help any excessive wear from happening?

 

Assuming the person who put in the engine won't do anything? Any place you purchased an engine from should've had a warranty.

I assure you these Cherokees aren't junk. They have two big killers, 1. Lazy previous owners 2. Rust

 

the place I bought the engine from only had a 30 day warranty. I didn’t even have that motor in the Jeep within those 30 days. I can’t point fingers at the guy who put it in either. Not necessarily his fault, I bought a used engine, he just put it in. I never liked the idea of buying a used engine. Although my Jeep is in really nice condition on the surface. The underneath was still slowly dying so I didn’t think a brand new engine was worth it but trying a used one was.

 

perform a compression, or better still, a leakdown test, that should give you an indication if the pistons or rings are unacceptably worn

these engines are regularly featured in "Top ten long lasting engines" , so you would have to be unlucky

thing is 100k miles, only takes a few episodes of overheating, or a lot of poor maintenace, and the damage is done

Also, its really about "cold starts" which is where most wear takes place, so a 20yr old engine is just that..unknown cold starts and maintenance

dont give up, lot of guys run with piston slap for ages

how was the bore in your old engine ?...saw an expert engine guy just pull a damaged piston out, hone the bore, and stick another one in

 

[QUOTE=Bk.randy;3596721 Most concerning is what I would call a knock. Is more distinct on cold starts and quiets up almost to a normal sounding engine when it’s warm. Almost sounds like a diesel, warm. [/QUOTE]

That is piston slap, 100%.
My 97 zj has it. In fact it has had it since I bought it with 150,k on it, now has 210k. Not really any worse. Goes away when warm. I've done everything else but the low block, did valve job, lifters, etc. With the head off you can move the pistons down and each one will rock noticeably in the bore at the bottom of the stroke. the 96 and 97s do have the mylar coated skirts, which I think helps. Dead quiet once it warms up.
I continue to almost daily drive it. After a minute or two, it goes away. When warmed up it's great.
However if it bugs you, and you are under a 30 day warranty, ....

 

it never completely went away warm. It used to have 5w-30 in it. Surprising enough, it seemed to be quieter with that. I put 10w-40 in just two days ago to see if it would make it more quiet. Actually made it louder both cold and warm. Now it doesn’t necessarily go away when it’s warm.

 

Well then I don't know. Claim your warranty before 30 days and / or drive it and see. If it's slap, and it never goes away, it's likely fubar.

 

.

 

if this link works, this is exactly how mine sounds in a cold start.

 

Doesn't sound too bad at all.