R171 M113 Tensioner Pulley

[E55BOF]

The SLK 55 spat its serpentine belt off today - the tensioner pulley seized. No noises, just the red battery/alternator warning, then about half a mile later the power steering became manual steering. Fortunately, I was only about a mile from home, so throttled off and used minimal throttle until I got there. The engine temperature rose no more than 10 degrees, so no other harm done, and the serpentine belt is fine too.

I'm pretty sure this:

Febi Tensioner Pulley V-Ribbed Belt 45875 - GENUINE - 5 YEAR WARRANTY | eBay

is the correct Febi pulley, as confirmed by their online catalogue. It's actually described as an 'idler pulley', though they also list another idler pulley which is identical to the idler pulley on my car; I think something has been lost in translation, because the website states: "The idler pulleys guide and hold the auxiliary belt in its entangled position..."

The seized tensioner pulley is a smaller-diameter all-metal item, with a lip on the side away from the engine, but this one is larger and has no lip. I've seen mention on one of the US websites (I think) that there are two versions, and that the later one (I presume this Febi item) will fit and do the job.

Can anybody confirm this?

 

[E55BOF]

Question answered, though not as I expected; what I can see is just the bearing from the pulley - the plastic part has completely disintegrated and fallen away.

 

[pmcgsmurf]

Sounds lie the bearing has maybe failed and ripped the plastic to bits.

£11.66 if you have Prime.

 

[Will]

Check the crank pulley harmonic damper too, they tend to wobble and the V-belt then doesn’t run smoothly as it should.

Would be a good idea to check all the other pulleys/bearings as well including the water pump?

No funny noises prior to failure, usually the bearings whine long before they give up?

 

[noogieman]

Best tensioner parts are INA, Litens or Gates.
I would stay away from Febi made in China

 

[E55BOF]

Check the crank pulley harmonic damper too, they tend to wobble and the V-belt then doesn’t run smoothly as it should.

Would be a good idea to check all the other pulleys/bearings as well including the water pump?

No funny noises prior to failure, usually the bearings whine long before they give up?

Harmonic damper runs true, idler pulley is a recent replacement by the look of it. Water pump spins quietly by hand. No unusual noises previously audible, but the exhaust is quite loud, and anything else would have to shout to make itself heard...

 

[slade1]

Had same problem with my CLK, about a 100yds from home. the shredded belt wrapped it's self round the crankshaft between pulley and block causing more aggro. I used OEM parts from MB.

 

[E55BOF]

Fortunately, on mine the belt came off entire with no other damage. It even looks still perfectly usable, but I might as well replace it anyway, so I will.

 

[E55BOF]

Doing the job tomorrow. Does anybody know what the tightening torque is for the bolt that holds the pulley to the tensioner?

 

[slade1]

To get the old tension pulley off you will need a locking pin, small Phillips type screw driver will do.
Torque, a bit off common sense here, how tight were the bolts to unscrew with standard Allan key or Torx key, I can't remember which.

 

[E55BOF]

No need for the locking pin; it wasn't very tight. No need for a torque wrench, either, just locking compound. It needs a T50 Torx bit, but one with the recess in the centre for the pip in the bolt head.

Doing the job without removing the rad fan and shroud, for which afaik you have to remove the rad, is an absolute pig because access is very tight, but I could get just enough room by undoing the radiator top mountings and tilting it forward. I lost some skin, but only a tiny bit of blood.

It was much easier on the E55K , because there was more room to work. f I had to do it again on the SLK, I'd bite the bullet and take the rad out...

 

[slade1]

M171 must be a different tension pulley to the M172 V6

 

[slade1]

Typo error M272

 

[E55BOF]

Unsurprisingly, yes, they are different. The M113 would be a five-minute job with the engine on the bench, but in the R171 it's a tight fit.