OM646 Serpentine belt tensioner oscillation

Discussion in 'Engine' started by selphy, Apr 19, 2015.

  1. selphy

    selphy Active Member

    Messages:
    96
    Joined:
    Mar 10, 2013
    Car:
    Mercedes E220CDi
    Noticed my tensioner oscillates quite a lot when idling. Is it normal?

    60K miles E220Cdi.

    https://youtu.be/SR3u6tGb2zk

    Thanks
     
  2. mersum1es

    mersum1es MB Enthusiast

    Messages:
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    Aug 9, 2012
    Location:
    Finland
    Car:
    W219, W220
    Bad freewheel clutch of the alternator?
     
  3. OP
    OP
    selphy

    selphy Active Member

    Messages:
    96
    Joined:
    Mar 10, 2013
    Car:
    Mercedes E220CDi
    Thanks for the suggestion mersum1es.

    I slipped the belt off - it was easier to release the tension than I had expected but I'm more used to working on transverse engines where there is only space to get a short ring spanner in and a couple of fingers in! With a 1/2" breaker bar I easily released the tension and the belt was easy to remove and refit.

    Anyway, I checked all the pulleys and I think they're all good. With the alternator armature locked I could turn the alternator pulley in only one direction and it was nice and smooth with just a little resistance. The other pulleys seemed fine also - a very slight squeak from the larger idler bearing but I reckon they're good.

    Does you have experience of how hard it should be to release the tensioner on this engine? I haven't seen many threads about the tensioner and idler bearing so can I assume they're not known weak points on this engine?
     
  4. Troon

    Troon MB Enthusiast

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    Aug 23, 2011
    Location:
    Staffordshire
    Car:
    A big one
    I would have expected to need a longer breaker bar than that! :D

    Seriously though, it's quite easy. I released mine to change the belt with a standard socket set ratchet handle without a lot of force. Hard to say if yours is tight enough, but it doesn't take a lot of force.
     
  5. OP
    OP
    selphy

    selphy Active Member

    Messages:
    96
    Joined:
    Mar 10, 2013
    Car:
    Mercedes E220CDi
    Thanks Troon,

    I read some useful information on the Gates website which suggested that significant movement of the tensioner when idling could be caused by a fault in the alternator freewheel pulley or the torsional vibration damper (by which I think they are talking about the cranskshaft pulley) and that these should be checked and that the tensioner should be replaced.

    Well I've checked the alternator pulley already and will take a chance on changing the tensioner. Hopefully the INA branded parts that ECP/CP4Less stock are of good quality. Life's too short to visit the main dealer for parts - I always find it an underwhelming and expensive experience and I don't even like their coffee.

    Any pointers on what to look for on the cranskshaft pulley? I used to run a PSA HDi engine which had a habit of eating through crankshaft pulleys - the tell tale sign on that engine was shiny metal filings. Is this the same on the Merc?
     
  6. OP
    OP
    selphy

    selphy Active Member

    Messages:
    96
    Joined:
    Mar 10, 2013
    Car:
    Mercedes E220CDi
    Good news: problem solved. I changed the tensioner, both idler wheels, alternator pulley and the belt for good measure.

    Less good news: I'm not sure which of the parts was at fault as they all seemed OK with no obvious sign of damage or excessive wear. However, it was a very easy and fairly cheap job as there is loads of space to work. All done in half an hour.

    Video link: tensioner with engine idling after parts replacements:
    https://www.youtube.com/watch?v=eKyV228XiEk
     
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