SZMB

First of all, sorry for posting this thread in this forum. I’m running out of ideas in trying to identify the cause of this problem. The members in this forum are fairly active and enthusiastic about their MBs, I’m hoping that I may get some help here from you guys. This is actually a 2004 CLK320 w/ 80k mi. Since the CLK320 shares the same engine as the E320, I’m hoping someone here may have seen/experienced this problem in their E320. Just recently, a loud low-frequency grinding noise has been coming from the front left (passenger side) of the engine compartment at idle. The noise seem to be loudest near the alternator, and it gets louder at higher RPM. However, there’s no loss of power. It’s still as powerful as ever. I removed the drive belt and checked out all the pollies by hand; all the pollies seem to be tight and the bearings are smooth. The noise sounds more like metal hitting against metal. See the video in this link.
http://www.youtube.com/watch?v=N5G-KL6RGGo

emilner

A pulley might feel fine while it is manually spun, but that is far different than when under tension and spinning at 1000 rpm. It sounds like a pulley might be the problem. I used to diagnose this by removing the belt and starting the engine to see if the sound is still there. I do not know off the top of my head what is driven by the MB belt (beyond a/c PS, alt etc), but I would imagine there would be no long term harm to try running the motor for 3-5 seconds with the belt off. If the noise is still there then the next culpret could be the cam drives.

emilner

You could also try hitting the pulley bearings with some WD40 while running, if the noise lessens or goes away than you know it is the problem (sometimes grinding bearings will show no change since they are far gone)...

SZMB

There's only one belt. Certainly, I can remove the water pump pulley and spray in some WD40.

emilner

I woud just pull the belt for a few seconds and see if the noise is gone before pulling pulleys. If it does go away then start spraying pulleys to find the culprit (if you cannot audibly tell)...

SZMB

With the belt removed and nothing is connected to the water pump pulley, does the alternator need to be driven as well in order to keep the car running for a few seconds and not resulting any damage to any electronics or mechanical parts in the engine? I have tried this on cars with two belts, i.e. with the AC compressor disconnected, but never on cars with just one belt.

no_mulligan

Try using a wooden dowel rod or stick around 24 inches long. You will use the rod like a stethoscope. Very carefully, touch the center of each pulley with one end and your ear on the other end. BE VERY CAREFUL around rotating equipment. Don't have any dangling clothes or jewelry on either. Sounds will vibrate the wooden rod. You'll know when you get close. Do this without taking any belts off. Good luck.

SZMB

Using a stethoscope sounds like a great idea. However, I won't use a wooden rod thought -- sounds kind of dangerous, I don't want to have my ear cut off while listening for noise. Ebay sells stethoscope for cars for around $10. I think I'll try to start the car with the belt off, the battery should be able to keep the car running for a short while.

http://cgi.ebay.com/ebaymotors/MECHA...motiveQ5fTools

DanG2

It may be the belt itself. It's a hard to be sure because the camera is moving around, but it appears from the video that the sound comes and goes in sync with the white flash on the belt. If the noise was from a bearing, I'd expect it to be more constant.

I'd take another look, and if that is really the case I'd try a new belt. If that cures it I'd double check the pulley alignment, and maybe the belt tensioner.

SZMB

After doing some more search online and in youtube, the noise seems to be from a failing alternator, where the bearing is making noise when under tension or load. This kind of grinding noise is well documented and has a distinctive sound from pullies and belts, and you'll find all kinds of articles about this problem when you do a search online. I'm going to use a section of the garden hose as a stetheoscope to confirm that the noise is from the alternator before buying a new/rebuilt alternator. Other videos posted on youtube had the same grinding noise from the alternator.
http://www.youtube.com/watch?v=ZBIktSdXLsU&NR=1
http://www.youtube.com/watch?v=Ya_rlzLZTOI&NR=1

Taylor-Made'90

My friend Douglas had the exact same grinding noise (on his CLK) and it was the alternator shaft bearings.



He got an aftermarket alty and it's performed fine. But he bought a alternator rebuild kit and attempted to rebuild his. He gave up (on it) rather quickly.

SZMB

I bought a stetheoscope from ebay for $10. After listening to different parts of the engine, the problem is definitely from the alternator. I highly recommend using the stetheoscope in identifying the locations of the noises. I just ordered an alternator rebuilt online.

health services

sounds like the idler pulley, I just replaced one on my SIL car. it is the upper most pulley. Pull the belts off and turn the pulley by hand if it is bad you should be able to feel it. I think it was less than $50 for the pulley at the dealer my cost.

health services

I missed this reply.

it almost sounds like a cage fell apart in your bearing.

vettdvr

That's what it sounds like to me also. If it is the alternator bearings be sure to change the idle pulley also. They are very small diameter high load and spin fast. This results in short life. Mine was replaced when I changed the belt at 80,000 miles. The bearing was rough but not failed totally.

I also bought a pulley from Autozone for about $20. Ok,, not MB part. However I looked at the pulley and bearing installed. Then I put the failed MB part in my lathe, machined it for bearing removal and found the bearing in the MB part was identical in brand and number to the AZ part at $25 less.

My guess is MB outsources the pulley to the same company.