My S55 has what sounds like a grinding or metal-on-metal, no lubrication bearing sound, mainly between 1000-2000 RPM. Definitely RPM related as the noise always occurs at that RPM range regardless of transmission gear/tire speed. It’s also strong enough to be felt as a vibration in the gas pedal. Want to start eliminating possible causes.

If I remove the supercharger belt temporarily as a troubleshooting step, A) would this cause any engine problems (other than reduced performance) and, B) would this cause a CEL by throwing a code?

Thanks in advance.
Cheers,
Jeff

 

Bump - Anyone? Any reasonable speculation? Any MB Techs out there?
Cheers,
Jeff

 

Make sure the engine is and the key is out of the ignition. The following procedure should not throw any CELs.

There are two belts on the m113k engine.
Remove and replace both of them as well as the plastic idler pulleys on each belt system. These pulleys are cheap and often fail at this age making a horrible noise you describe. They are identified in your OM. Take a pictue of the belt assemblies to get it right when you reassemble. I got my parts from Sponsor www.mymercedesparts.com. Have your vin ready and let them know you are an MBworld member.

With the belts off, Spin the other pullies. If they make any noise such as you described replace them.
keep the old belts in a box of spares in your trunk.
Given the age of the car this is a recommended service. Good luck!

 

Is this noise present only when there is a load on the engine (I.e. driving) or an you recreate the noise I. Your driveway by revving the engine to 1000-2000 RPM's.

 

Thanks Grane for the information. However, prior to writing the thread, I had replaced the double pulley assembly (p/n 113.202.04.19) as the outer pulley bearing (which runs the compressor) was incredibly wobbly. Thought for sure that was the problem, but it wasn’t. Of course, I changed both belts at the same time as they had developed ‘belt chirp’. Unbelievably, the noise is still there. What I suspect (with a heavy heart) is a bearing within the supercharger. So what I want to do is run the engine temporarily (less than 5 minutes) without the compressor belt. I would leave the main belt installed, of course. It is under this condition that I am hoping not to trigger the CEL. Nevertheless, I will re-inspect the remaining idler pulleys for the main belt, for while I did inspect them, it was only a cursory look.

Good question, MBtech1098. The noise is most noticeable under load, but present (albeit, far less noticeable) while at a dead stop and just revving the engine. Very repeatable, very predictable, very metallic (meaning, not sheet metal rattling or any ‘tinny’ sound). It is *not* a main bearing deep thump/thunk and I do not sense that it has a rhythmic frequency tied to the RPM’s. It’s more of a grinding sort of noise (like a worn ball bearing) but so severe in intensity that it can also be felt through the gas pedal. So I suspect it’s a bearing of some sort. Slightly more noticeable when the engine is cold.

I freely recognize a description of a sound is tough, if not impossible, and I am really not trying to describe it here. What I want to do is begin eliminating sources of bearing noise. Easiest is the blower by running the engine without the compressor belt for less than 5 minutes. But I do not want to create CEL codes, if I can avoid it. Next would be any auxiliary assembly (AC Compressor, etc.) that is tied hard through brackets to the engine. But leaving the main belt off will, no doubt, throw a code.

One more tidbit. If you look a couple entries back in this M113 Forum, you’ll see where I described a severe vibration at ~2,500 RPM. Replacing the 3 mounts made the vibration go away. But I clearly didn’t solve the problem. I suspect the root problem there and this problem are the same. Replacing the 3 mounts simply masked the vibration… until the transmission mounts fails again. Whatever is causing this bearing/grinding type of noise, also causes (I believe) severe engine vibration – enough to tear the transmission mount.

Any thoughts or input from all is greatly appreciated.

Cheers,
Jeff

 

Is it possible for you to record the noise you are experiencing?

 

You can inspect the idler pulleys with a dentist type mirror for cracks in their rear side but given their age, low cost, and the fact you have the belts off I would just replace them. Why chance ruining a good belt? Make sure the belts are not too tight but I don't know what the exact procedure is to determine such.

Since you are an MBCA member there was a tech article on this in the STAR they is probably on the website. You might want to submit the question there to George Murphy.

Somewhere on this Thread or elsewhere there is a discussion of replacing the S/c pulley, bearing and Mobil Jet oil if you search. Hope it's not that but it's better than replacing the "lifetime" supercharger unless you have an extended warranty.

Good luck.

 

Yes and no. The recordings I made do not adequately provide a good audio of the noise. When in the driveway, the noise is too subtle to be adequately distinguished from normal engine noise. When driving, the noise is present but road noise then begins to drown it out. The noise is not like hard bearing knock, tappets, or anything rhythmic. My noise is similar in nature to a combination of muffed throttle growl (as when you punch the accelerator and the sudden in-rush of air creates that distinctive throaty, 'howl' sound) and sandpaper being rubbed over concrete, just not as loud. Odd combination, I freely admit!

The 'howl' sound I attribute to the compressor. It's the subtle sandpaper-on-concrete sound that bothers me, and the fact that I feel the vibration sensation in the gas pedal at the same time. Above 2500RPM and things smooth out and quiet down; strongly suggesting a bearing of some sort. Or a harmonic balancer (?).

Thus, I want to troubleshoot this problem by elimination. Removing belts and such would be a logical start to isolate the noise. But at the same time, I do not want to throw a CEL code, if I can help it. If I have to, then so be it and I'll deal with the code(s). I assume removing the compressor belt would not damage the engine.

Cheers,
Jeff

 

No damage will occur by taking of the kompressor belt. Also the CEL may or may not come on, however that is not a big deal, just clear it of it does.

 

OK... Removed the compressor belt and drove the car about a mile or so. No CEL and no codes appeared. Noise is still present but less intense suggesting that removal of the compressor belt had an effect. Considering the compressor is still in motion when the engine is running, I'm really leaning toward the compressor bearings. Once I get a can of Mobil Jet Oil, will change the compressor fluid to see if it reduces the 'grind'.
Cheers,
Jeff

 

So, using a 5mm Allen ball-wrench, a large syringe and a bit of aquarium tubing, I sucked out a whopping 3 tablespoons of compressor oil. Yup, only 3 tablespoons! Smelled horrible and was pitch-black. Cleaned the syringe and pumped into the supercharger ~3/4 cup of Mobil Jet Oil II. The color of the fresh Jet Oil is a clear orange. Obviously, my supercharger was in need of some serious servicing!

Immediately after starting the engine, it sounded better. The vibration ‘felt’ in the gas pedal is gone and the grinding noise is much reduced. While my compressor wasn't 'dry', it was not being properly lubricated. The continued grinding noise, albeit reduced, suggests the bearings have worn excessively.

Because of the severe condition of the compressor oil I removed (what little there was) I'm going to do another compressor oil change in a week or so. That should get virtually all the old stuff out. Even then, I'll have plenty of Jet Oil left over for multiple future changes. Shelf life is outstanding for this stuff. Time to change the compressor oil was a comfortable 20 minutes.

Cheers,
Jeff