W210 E320CDI engine rattle

[IanT]

Since getting my 210 there's been a rattle that sounded like something metallic under the bonnet. Jay had a look but as it only happened while on the move at gentle throttle, it wasn't easy to diagnose as being anything different to the usual combustion irregularity that happens sometimes on these engines at 100k miles.

Recently I noticed it happening at idle and investigated as much as I could without a workshop, and there seems to be a metallic 'tink' noise irregularly coming from the front of the engine bay, possibly low down on the drivers side. Running isn't affected, but it seems to make the noise whether warm or cold, sometimes making a louder one and then stopping for a while. I've turned all consumers off, so items like AC aren't running, but I can't diagnose it.

It seems to go away under hard acceleration (while the throttle is blipped) but returns after the revs come down near to idle again.

I've probably got too much mechanical sympathy for it and so being ultra cautious with an undoubtedly expensive engine I've not driven it for nearly 3 weeks now and am obviously missing it.

Are there any obvious things to check?

I've removed the radiator fan cowl and can't see how to remove the viscous fan and auxilary drive belt to rule that out of my diagnosis. Can anyone shed any light please?

Cheers,

Ian.

 

[IanT]

Thought I'd give this a gentle bump before I concede and take it to a garage. I'd take it to Olly on the South coast but am not confident that driving it any distance is the right thing to do.

I've had a recommendation to use Wright-Tech (Andy Wright), who is very local to me and used to be in Orpington trading as Merc-Tech until very recently.

If there's something I can do while the bits I took off are still in the boot, that'd be great.

Cheers all,

Ian.

 

[_Taz_]

the viscous fan & aux fan are driven by a piece of garter belt that is hidden behind the steel frame / brace that holds the fans in position...

been there when I fitted a new A/C condensing RAD, after the old one had a hole, cause comically enought by a stone that had wedged behind the motor & machined a perfect circle through the face of the rad

Amazing at costs, tho', approx' £300 from MB, europarts £120, fitting was easy, not perfect but it works now !

If it's by the RHS lower bay it could be an engine mount / turbo area, possibly loose studs ?

 

[Dunhamkid]

Fan belt tensioner?

 

[tmaoahthfte]

Alternator pulley?

 

[IanT]

Thanks for the suggestions everyone, I dropped it off at my most local indy on Thursday last week, will hopefully hear back tomorrow when he gets chance to look at it.

I had already had a good look around, but there wasn't anything obvious anywhere and so without knowing exactly how to take it to bits I didn't think I should really get stuck in too much. I couldn't see how to remove the viscous fan for example, nor how to take the tension off the aux belt so as to remove it, or otherwise I'd have done so and then run the engine to see if the noise disappeared.

I'll post back when I hear more, I don't normally use any garages as I'm normally of the opinion that cars should be mostly DIY for mechanical matters.

Ian.

 

[IanT]

Alternator pulley?

Have a gold star.

That's exactly what it was, there's a one-way bearing fitted to the alternator pulley that is there to smooth the spooling of the auxiliary drive belt at low revs, and it was this that had failed. The car is now quieter at idle and that tapping noise at low throttle has now gone.

The other two pulleys were also changed as their bearings had gone dry so hopefully I'll need no further maintenance in that area for a while.

From memory, before I bought my last 210 (220CDI) it had suffered a more severe failure of that component and needed a new alternator as well as a number of other parts, so I'll consider this to be a small disaster averted.

Thanks for the suggestions.

Ian.