The noise is clear during idle and it's coming from front of the engine. But it goes away when I push on the accelerator. My friends insist that it has to be a bearing or something similar in one of those pulleys.

But I thought if it was a bearing, then it should be making noises at any rpm, not just during idling.

I have searched the forum and some mentioned the similar symptoms with a fix of changing motor/trans mount. Can the engine mounts failure cause these nailing/vibrating noise @ idle, and quit at acceleration?

The Benz is the 96 E 300 D.

What failures will cause engine nailing noises during idle but quit at higher rpms?

Hard to say. The alternator pulley freewheel is only active at idle. There's more engine vibration at idle, so mounts could be it. Could also be injector nailing that goes away, I suppose.

You really need to get out the stethoscope.

The eaiest way to check the accessories is to drop the tension from the belt and check each pulley by hand for drag or noise.

To confirm you can also run a "cold" engine for 30 seconds to see if the noise is present with the belt off.

The tensioner damper shock bushings can sometimes cause a rattle noise.

I had vibration at the tensioner assembly that was due to a bad motor mount also.

First thing to do is pull the belt and check the other pulleys.

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Terry Allison
N. Calif. & Boca Chica, Panama

09' E320 Bluetec 77k (USA)
09' Hyundai Santa Fe Diesel 48k (S.A.)

I would put my bet on tension dampner shock or the bushings with it.

__________________
-disav

99 E300 TURBODIESEL Astral Silver 282K - AMG brakes, suspension, monoblocks, speedo & interior - Full Load Maxed on IP by custom Speed Tuning USA Chip - T3/T4 Garrett - EGR/MAF delete
98 E300 TURBODIESEL Alexandrite Green on black leather 289K
95 E300 DIESEL Green Queen 267K SOLD
84 300D 216k SOLD
87 300D 299K #22 head - intercooler - full load adj. - 8sec 0-60mph - SOLD
76 300D 214K SOLD

I second (or third) this...99% it is the bushing...but you need to replace the whole shock.

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Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz

Thanks for all the tips guys! I will check out each of the listed possibilities and will let you guys know the result.

One thing puzzles me is the fact that the noise is present during idling only and completely disappear on a slightest push on the accelerator.

So, can a bad bearing be one of the possible problems? is it highly?

When you guys talk about the dampener, is it the strut looking like thing( but smaller) located in front of the engine? below the valve cover level?

That would be it. Is your noise random, or consistent? If it was an injector I'd think it would be consistent; my E300 has a random ticking (also only present at or slightly above idle) which I suspect to be the tensioner.
I believe a bad tensioner can also lead to premature fan clutch death...a bad tensioner on my engine would also explain why my fan clutch is going bad for the second time in a few months.

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99 E300 TD -- sold
01 540i 6 spd

Mine had the same noise only at idle...it was the tensioner shock bushing. It only does it at idle just because that is the same frequency as the shock happens to resonate at.

You might want to consider new motor mounts when you replace the tensioner shock as I have heard that bad mounts can cause premature failure of the shock/bushings due to the extra vibrations being transmitted through them from the way the engine shakes more at idle.

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Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz

I am having problem trying to find the place that sells the dampener/tensioner ( not local MB dealer yet, of course). Where do you guys find them at? I have looked through Mercedesshop.com, couldn't find it.

http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1ZT1FAGUU20Q0QEQ3S&year=1996&make=MB&model=E-300D-002&category=G&part=Acc.+Belt+Tension+Damper

Its on the cooling system page.

Before getting a damper, remove teh spring and drop the belt and test the other bearings first. Then start it and see if the noise is gone or not. If the sound is still there, its not related to the belt.

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Terry Allison
N. Calif. & Boca Chica, Panama

09' E320 Bluetec 77k (USA)
09' Hyundai Santa Fe Diesel 48k (S.A.)

IIRC the OEM part is just about the same price as the aftermarket so you might just want to check with the dealer...normally they stock them too.

Terry's suggestion to isolate the belt drive accessories is a good one, that will assure you that you have found the source of the noise.

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Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz

The OEM part is a Bilstein shock, so if thats what your parts counter sells then get one of those.

Note that its likely that only one bush has failed - the other may still be ok. So either push that bush out and keep it, or keep the old shock. If the new shock fails in time, you can just swap the bad bush for the good one.

I'd also get a tensioner spring as well - since they can snap suddenly and the car is undriveable without it.

Thanks for all the help, guys! I will definately drop the acc. belt first to check for the source of problem before ordering the tension dampener.

A failing alternator can cause the tensioner spring to make noise. I have had a little intermittent nailing at startup for a while, but it got much louder about a month ago. I raised the hood and heard a loud "twang" (sort of like dropping a coil spring on a concrete floor). It made the sound a couple more times before the engine got warm, and then it stopped. I couldn't find the source, but it did it every time the engine was cold. I was concerned I had a serious problem, so I took it to an independent shop. It took them a while to diagnose the problem, but they said something in the alternator was binding which caused the belt to jump occasionally, and then the tensioner spring would make the noise. A new alternator cured my noise. They said the tensioner was still in good shape.