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Unread 08-21-2013, 07:36 PM   #1
paroxysym
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Loose crankshaft pulley?

So I've noticed a banging/rattling at idle so I crawled under my jeep and have kind of pinpointed it to the front bottom end of the motor. I want to say its the crankshaft pulley, however I am wondering what else it could be? It's a 4.7 with 115k on her.

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Unread 08-21-2013, 09:10 PM   #2
WieSeL
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You have to look at it really. Use a stethoscope or a screwdriver to try and pinpoint the area of the noise. Definitely could be your harmonic balancer
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Unread 08-22-2013, 10:38 AM   #3
blue3
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Quote:
Originally Posted by paroxysym View Post
So I've noticed a banging/rattling at idle so I crawled under my jeep and have kind of pinpointed it to the front bottom end of the motor. I want to say its the crankshaft pulley, however I am wondering what else it could be? It's a 4.7 with 115k on her.
I haven't done this with my jeep, but on my other car I've taken the belt off to spin each pulley by hand, to narrow things down. Using the stetho/screwdriver is another way to do it if you are able to safely get in there with things spinning.
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Unread 08-22-2013, 06:08 PM   #4
ca07wk
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Try turning the crank pulley with a breaker bar
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Unread 08-22-2013, 07:38 PM   #5
WieSeL
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Quote:
Originally Posted by ca07wk View Post
Try turning the crank pulley with a breaker bar
What's that going to do? A harmonic balancer will usually only make noise with a load on it at eng speed. Sometimes it won't make noise with the belt off running but will be loud as hell with the belt on

Check the AC compressor. It's close to the balancer and when a clutch gets worn it will rattle. Does it make noise with AC on and off? If the sound goes away with AC off it the AC clutch, noise with it on, the compressor.
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Unread 08-22-2013, 09:05 PM   #6
90grandoneer
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Quote:
Originally Posted by ca07wk View Post
Try turning the crank pulley with a breaker bar
I am sure he's saying that to see if the bolt is loose. Ain't no way that'll happen, unless someone has had it off and didn't properly retorque it. Also, haven't seen nor heard of a balancer going bad, but it sure is possible. I would think that if that's the problem and it's that bad, it would be easily visible. In any case, if it is the balancer, better change it ASAP. You certainly don't want to see the damage it can do if/when it completely lets loose. You'd probably be replacing almost everything on the front of the engine and maybe the cooling fan and radiator, depending on the RPM at the time.
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Unread 08-22-2013, 09:34 PM   #7
WieSeL
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Oh ok i seee. It's a pressed on pulley. You need a puller to get it off. If the bolt was loose it may not even start to work it's way off. True they don't go bad often but it definitely does happen. Seen it the other day on a Buick v6. The rubber inside breaks down, but doesn't necessarily mean it's going to fly off. Well worth trying to torque it with a breaker bar but you will most likely turn the crankshaft before it will thread the bolt any tighter unless very loose.
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Unread 08-22-2013, 10:25 PM   #8
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Just look at the damper pulley with the engine running,if it is wobbling all over the place it's bad.I probally have replaced 10 or so bad ones on 4.7's over the last few years.One was so bad it actually put a hole in the front cover,was a dumb luck it did not come off and do more damage.
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Unread 08-23-2013, 04:20 AM   #9
Umbrella
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The harmonic balancer went on my WJ 4.0.

It definitely does happen.
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Unread 08-23-2013, 07:06 AM   #10
paroxysym
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i have yet to remove the belt, i did notice yesterday sitting in the drive-thru at the bank that if theres a load on the engine its intermittent- where as when i had it in neutral it was more apparent. i also here it when i hit a bump- so im thinking something is loose. i may remove the front skid this week to see if that MAY be the culprit as the shop i took it to removed it last time to do my oil change.

ill keep you posted, but i appreciate the feedback and hope it keeps coming

Umbrella, how much did that cost to replace?
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Unread 08-23-2013, 10:16 AM   #11
90grandoneer
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Wiesel is exactly right on how the pulley is constructed. Like I said, there is no way the retaining bolt would come loose, unless someone had it off previously and didn't properly re-torque it. And, yes, it is a press fit (requires a puller to remove), but there is no keyway....except on the aftermarket UD pulley that I have on mine.

The stock pulley has 3 "spokes" that you can get a pry bar through and wedge against something on the engine. This will allow a re-torque. The SLP UD pulleys I have on both my Hemi's don't have any spokes and a strap wrench must be used to stop the engine from turning over when torquing. IIRC, the torque is ~125 ft. lbs. That's why I say it'll never come loose, unless someone has messed with it before and didn't re-torque.
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Unread 08-25-2013, 05:30 AM   #12
Umbrella
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Quote:
Originally Posted by paroxysym View Post
i have yet to remove the belt, i did notice yesterday sitting in the drive-thru at the bank that if theres a load on the engine its intermittent- where as when i had it in neutral it was more apparent. i also here it when i hit a bump- so im thinking something is loose. i may remove the front skid this week to see if that MAY be the culprit as the shop i took it to removed it last time to do my oil change.

ill keep you posted, but i appreciate the feedback and hope it keeps coming

Umbrella, how much did that cost to replace?
On the 2000 4.0, a harmonic balancer costs less than $40.

Not sure about a 3.7/4.7/5.7, but doubt it is too much.

I have a 3-jaw puller and changed it myself, 20 minutes.

Here is a link to a good thread on it, including an explanation by Mrs. Umbrella a.k.a. "the wife" on how it felt when it let go. LINK
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