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I have a 2008 Dodge Avenger with 2.4 liter 4 cylinder engine and 4 speed automatic transmission. Odometer reading is 80750 miles. Engine has developed over the last several weeks an ominous noise from the valve train. This engine has a chain driven exhaust camshaft and intake camshaft with variable valve timing. Both when the engine is cold and after warm up there is a very noticeable noise coming from the crankshaft pulley head of the head. It definitely sounds like it is coming from the camshaft drive area. At times it is a whirring noise, some knocking and occasionally some popping in this area. It is even noticeable from within the cabin area when driving at slower speeds of 10 - 20 mph.

I removed the serpentine belt accessory drive and turned all the pulleys. The belt tensioner pulley was making noise so I decided to replace 2 fixed idler pulleys and the tensioner pulley. Noise level is still about the same. So I decided to run the engine without the accessory belt in place. Good news. The noise is not present. So my idea that there was a problem in the valve train is wrong.

So the issue is how to determine which accessory is creating the noise. I turn the water pump, AC compressor shaft, power steering pump and they all seem smooth. I am leaning towards the power steering pump since that has internal rollers that move along an oval track inside the pump. The water pump only has an impeller and a bearing and the alternator just has slip rings and bearings. Any thoughts on how to accurately determine which accessory is creating the noise?
 

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I'm glad that it doesn't seem to be internal engine.
You can put together a make-shift stethoscope with a punch and a piece of rubber vacuum hose. The vibration damper/crank pulley can make this kind of noise if it is coming apart. The variable displacement axial A/C compressor can also make this kind of noise (there may be no compressor clutch). A cracked accessory bracket can also be silenced with the belt load removed from it.
Listen around with the stethoscope to locate more closely the source of the noise.
 

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Discussion Starter #4
Jeff2KPatriotBlue said:
First, try topping up the Power steering.
I checked the power steering fluid and the level is right at the ADD mark so I believe there is sufficient fluid.


You can put together a make-shift stethoscope with a punch and a piece of rubber vacuum hose. The vibration damper/crank pulley can make this kind of noise if it is coming apart. The variable displacement axial A/C compressor can also make this kind of noise (there may be no compressor clutch). A cracked accessory bracket can also be silenced with the belt load removed from it.
Listen around with the stethoscope to locate more closely the source of the noise.
The A/C compressor is a variable displacement that is controlled by the engine computer so there is no clutch on the pulley nor clutch bearing. I engaged the A/C control on the instrument panel to put a load on the compressor but there was no difference in the sound. That should cause the compressor wobble plate to move and force the pistons to oscillate if that were the noise source.

I thought that when I turned the power steering pump I felt a few hard spots. Now that the engine has cooled everything turns smoothly. So more detective work. I like the idea of a make shift stethoscope so I will try that. Thanks.
 

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I tried using the make shift stethoscope. I touched the metal punch to the body of the power steering pump and the alternator but I could not detect any more appreciable noise.

Last night I removed the remote power steering reservoir and emptied it of fluid. I then disconnected the hoses to it and inspected the filter in the bottom of the unit. Since the housing is translucent it was easy to illuminate with a bright light. The mesh filter has some minor spots or blockage. I reversed flushed it with solvent, let it dry and then re-installed and added some ATF+4 transmission fluid. I believe the mesh filter is NOt starving the pump for fluid and causing noise.

I started the vehicle engine and there was minor noise. The power steering pump was at ambient temperature since it had not been operated for several hours. I decided to add some fluid to the reservoir and as soon as I added about 1 teaspoon, the knocking and catching noise started immediately. I do not know if that is just a coincidence or that indicates there is an internal problem with the roller cam inside the pump.

I let the engine run for about 2 minutes and then stopped it. I removed the serpentine accessory drive belt and attempted to turn the pump pulley by inserting my finger in the spokes. There was some resistance as one would expect. I spun the pulley for about 2 minutes and then all of a sudden the resistance vanished. It was like the unit was not pumping. You could spin the pulley as fast as possible manually and it would spin down in 2 - 3 seconds. That seems to be strange behavior. Maybe I am heading in the right direction.

I have a spare 110 volt electric motor with pulley that I am going to try and rig a belt drive from it to the power steering pump. If I can spin the pump by itself I should be able to determine if that is the problem or need to move on to the next accessory.

This is the first vehicle I have seen with the decoupler pulley on the alternator. It is good to know that it can be a noise source. On the Avenger I spin the alternator and there is no noise from the bearings at least and no electrical charging problem.

Thanks IC for the tip about the alternator. I never realized that could be a noise source.
 

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Discussion Starter #7
I rigged up a 110 volt 1/3 horsepower electric motor with a belt and connected it to the power steering pump. The motor was laboring to spin the power steering pump as there was fluid in the system. I ran it for about 20 seconds and there was no knocking noise.

I then attached the electric motor to the alternator and spun it. No noise from it. I then attached the electric motor and belt to the A/C compressor pulley and no noise there.

So the situation is real elusive. Obviously the serpentine belt needs to be in place to put mechanical load on each accessory pulley.to cause the knocking noise to become audible. So that tends to make me think that the alternator decoupler pulley (which is just an overrunning, mechanical clutch) is suspect. But again this is just guessing.

I could take the vehicle to a Chrysler dealership service department but will I just get more guessing???? A $75 - $100 diagnostic fee could be applied towards a replacement alternator??? In situations like these I can certainly understand why repair facilities and vehicle owners ALL get frustrated!
 

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I took the vehicle to a dealership service department to get another opinion about the noise. I was told that it was the alternator bearings making noise. I probed for further clarification and asked if it was the decoupler pulley. All I was told was that Chrysler does not supply the pulley separately so that was a round about way of telling me that the pulley was causing the noise.

So I purchased a rebuilt alternator complete with new pulley and will install it. So this problem is resolved. Since I drive older Chrysler vehicles I have never encountered a problem with the over running clutch which is just another name for this decoupler pulley. It is truly sad to have to replace an alternator because the pulley fails. I am sure the bearings and brushes still have many miles of service left in them.

Why engineers tinker with something that is reliable and in the process shorten the life and reliability is just stupid in my opinion. But many other manufacturers including popular imports use the same pulley design. What ever happend to K I S S : keep it simple stupid!

Thanks to Imperial Crown for sending me in the right direction. I would never have thought an alternator pulley could create noise.
 

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As an engineer, I can tell you that I have never seen a requirement to make something last as long as possible. Not even long term nuclear waste storage!
 

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Jeff2KPatriotBlue said:
As an engineer, I can tell you that I have never seen a requirement to make something last as long as possible. Not even long term nuclear waste storage!
I would agree that maximum longevity is not necessarily advantageous. And if you wanted something to last a long time, would a manufacturer be able to make it cost competitive. Probably not.

Chrysler pioneered the usage of alternators in 1961 on all its car lines. It provided some electrical charging during engine idling conditions which was certainly advantageous. Due to its design that promoted long life because the slip ring brushes only had to carry a minute current. This allows alternators to run many, many miles before wear takes its toil. It is not unusual to get 150,000 - 200,000 miles from an alternator before brush wear or bearing wear causes a failure.

Now manufacturers put this entirely mechanical decoupler pulley on a long-life item and the over running clutch mechanism fails prematurely. The idea is to get smoother running and less vibration from the accessory drive belt system. Oh I guess that might be a selling point for a vehicle but to compromise durability that severely for nebulous results seems to be a step backward.

Or is it possible the engineering idea behind usage of the decoupler / over running clutch pulley is sound but implementation is compromised with poor quality materials or poor internal design or poor assembly procedures?

If you do an internet search on this pulley design you will find lots of information about failures across many manufacturers vehicle lines. I am not trying to start a fight but I just have to wonder what thinking (or lack there of ) goes on with engineering manufacturing today. OK. I will step down from the pulpit!
 

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Those alternators with the decoupler pulleys are also a know problem on the Calibers. It's easier and almost as cheap just to replace the whole alternator. As mentioned by IC, it takes some special tools and know how. I have neither, I just know that a LOT of Caliber owners have been through this.
 
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