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Noise from front end

Hmmm...I have yet to master mind the internals of a 4.0 because the deepest failure I had was needing to replace my intake. However, I have a Subaru Legacy that I have diagnosed with a bad timing belt. I ran the engine with timing cover off and observed the belt, it was jumping a bit and quite loose. It has however driven 3000 miles since then with no power issues or anything, great MPG, smooth idle. The noise in your video is so identical to the sound and rhythm of your Jeep. I was able to pry on the failing hydraulic timing tensioner and when I applied manual tension, the noise cut out immediately. I don't know if a 4.0 can be ran with a simple removal of a few bolts like a subie cover, but when your watching the engine run with the cover off, wherever a tensioner is, if their is a way to simulate full tension with a screwdriver or something, see if that correlates to the noise going away. Otherwise, ground the cylinders one at a time and see if any certain cylinder being cut out removes the knocking/slapping noise. Try a stethoscope from an auto parts store and probe around for an area where you hear it most. Do a compression test, pretty easy. Valve cover is easy to remove also, then you could atleast do a quick visual inspection for anything obvious valve related, and also have a good opportunity to replace the cover gasket.
 
It kinda sounds like a timing chain to me. I think you may have more than one problem.

As I remember it there is nothing act as tension, like a Subaru, only a piece of plastic in the timing cover.

There are a few test to check the timing belt without taking it apart. But I'd replace it anyway and double check the flex plate just because so many odd problems can be related to it. And of course the harmonic balancer, even if your low mileage it is the years.
 
The harmonic balancer is new and the timing chain is the original but I haven't tore into the rear end to maybe look at the torque converter bolts. I did take the drive belt off but the noise is still there. It doesn't sound like any parts in the valve train. I guess I will have to replace the timing chain and hope.
 
My bet is on the timing chain or something internal. It fluctuates with prm but it's not instant. once the rpms drop you can hear the chain still scraping for a little bit like it's deceleraring. Torque converter bolts doesn't sound like a deceleraring noise.
 
Have you taken a peek at the pulleys to see if anything looks out of balance? I have had a bad harmonic balancer on a few trucks, ending up just scrapping them, but every time I had a bad balancer I could see my crank pulley wobbling a slight bit and I always noticed belts getting wore down quickly. Now that I tore my timing cover off out of curiosity, I notice their is indeed no tensioning system, just two gears. So that leads me to think you have a bad balancer, or timing chain is old enough to become loose. It actually isn't as hard as I thought to get to the timing chain. Didn't need any crazy tools and I did it in the snowy driveway at about 25 degrees. Good learning experience. Mine has 235xxx original miles and my chain seems good as could be. Must be something else that is more likely to fail and contribute to tension loss.
 
One possible way to check if your chain is to worn. Pull your dizzy cap off and rotate the engine one way and then back the other way using the harmonic balancer. Watch the dizzy rotor. If it moves instanlly then your good. But if there is any sort of pause in motion or a lag in movement I suspect your sir need a timing chain. The chains wear at every single link piviot. It's amazing what stacked tolrences will do.
 
Dragonlich1961 said:
One possible way to check if your chain is to worn. Pull your dizzy cap off and rotate the engine one way and then back the other way using the harmonic balancer. Watch the dizzy rotor. If it moves instanlly then your good. But if there is any sort of pause in motion or a lag in movement I suspect your sir need a timing chain. The chains wear at every single link piviot. It's amazing what stacked tolrences will do.
Click to expand...

Well I just learned something, cool way to test it.

OTOH, I just had a power steering pump self destruct that I was sure was a timing belt (not on a jeep, on a 2001 saturn) but like a jeep, the power steering pump is close to the valve cover. It seized up and smoke the new serp belt while I was turning the steering wheel
 
I was getting a strange scrubbing sound from my 1997 XJ (183,200 mi) which I couldn't really localize. It was at the front of the engine, but not on top. The front seal in the timing cover was leaking anyway so I decided to replace the water pump, tensioner pulley, and timing chain and sprockets. And the front seal, of course!

When I opened the timing cover I found the rubber snubber had hardened into stiff plastic and one of the ears that held it in position had shattered so it was no longer held in position very well. When I went to replace the camshaft sprocket I found the new Cloyes sprocket's indexing hole wasn't in the right place radially (along the line from the hub to the teeth) so it wouldn't go over the indexing pin on the camshaft. I don't know the history of the engine so I don't know if the camshaft is the original and Cloyes made an error, or if the camshaft is 3rd-party and it's at fault, not Cloyes. In any case I just replaced the chain and rubber snubber but didn't replace the sprockets. The old chain and sprockets were worn enough for a 0.3" deflection -- the FSM says if the deflection is 0.5" or more they should be replaced. By replacing only the chain the deflection was reduced to about 0.2", plenty good enough for me. The part that really needed to be replaced was that little block of rubber!

When I had pulled off the water pump its bearing felt OK, but things sat for 2 days while I was called away to work on something else. When I was ready to put on the water pump I checked the old one and the bearing felt quite rough. Evidently the lack of use and the fact it had dried out made its failure more apparent. Of course I used the new water pump. For some reason I reused the old tension pulley, thinking its bearing felt OK.

After buttoning everything up I started the engine and Damn!! there was still a scrubbing sound! I wasn't happy at all. Tried readjusting the serp belt but it didn't help. Then I replaced the tension pulley and all was well.

So I had 3 things failing:
* The rubber snubber in the timing cover
* the water pump bearing
* the tension pulley bearing
 
tylergrant2011 said:
Where can I buy a stethoscope
Click to expand...



Got a cheap one from harbor freight. Under $10 if I'm remembering right. Amazon, most car parts places have something. The more you spend on it the nicer it is, the el cheapo one works fine.

Picked it up to locate a odd sound from the front then the new idler pulley self destructed and I replaced everything that spins up front. Even the bloody power steering pump because I broke the reservoir return. Such a brittle plastic, snaps easy.

It really is interesting to hear what going on, which can be hard with the 4.0 making its usual noises.
It's a good diagnostic tool IMO .
 
The thing that concerns me is with the belt off it still makes noise and that eliminates everything but the harmonic balancer that is on the drive belt
 
You should be able to see any problem with the harmonic balancer now, like the rubber guts coming loose or the outer part wobbling and hitting something like the chain cover in the back side. They are not expensive and not hard to change.
 
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