M272 Serpentine Belt Idler and Tensioner failure and replacement

[Blobcat]

Sat waiting for garage door to open tonight and thought “that’s a strange noise the door is making”. Then realised I could smell plastic burning...

Engine off, bonnet open, front engine cover off and bits of belt strewn around

Top idler wheel completely gone...




You can see bits of the idler I recovered from deep in the engine bay



The tensioner looks like the newer type with 17mm release nut. So do I just need a new idler and belt?

Its bleeding (well my hands will...) tight at the front of an SLK so any tips on replacement appreciated.

I’ve changed the belt on the 911 when I had the alternator rebuilt, this looks about as tight.

I‘m guessing genuine MB parts for idler and belt - unless there are other recommendation.

 

[sonic]

You couldn't have had a better place for it to happen? A fairly rare happening, how many miles has the car done?

 

[Blobcat]

You couldn't have had a better place for it to happen? A fairly rare happening, how many miles has the car done?

Just over 95K, I did hear a “squeak” when I started it a week or so ago, I was going to let @Cole@MBS look at it at the next service, although that is ~5k miles away.

 

[mioba]

Great time and place for it to fail and good you got it when you did. Snapped belts can cause alot of damage if they go flying.
Original MB parts all the way. You know the drill!
Check your other pulleys too, to ensure they are rotating freely and for excessive play. If any are not right change them (its only a bolt).
There are tonnes of vids on youtube. I changed the belt on my W251 this year as precaution.
A small wrench with a long handle helps due to the narrow gap.
Get the torque from the dealer. They are not that high and can easily be undone.
Make sure no damage at all to the other pulleys and the grooves are perfect.

 

[Uncle Benz]

Common failure that. Easy fix. I can’t quite recall if it’s one with the long bolt, but if it is you just need to turn the fan to a point where you can slide it out. Spin the others while the belt is off and listen for harshness. Worth eyeing the tensioner for leaning over too while you are there. No biggy, lucky it didn’t fail out and about.

 

[mioba]

Oh and check your tensioner too that its not sticking. Also easy to replace. They come with the locking key in.

 

[rifiki]

Had same problem with M272 CLK about 100 yds from home. May need small Phillips screw driver to use as locking key.
I changed the idler and check bearings on alternator, water pump etc.

 

[Blobcat]

Had same problem with M272 CLK about 100 yds from home. May need small Phillips screw driver to use as locking key.
I changed the idler and check bearings on alternator, water pump etc.

I'll see what I can fit in the tensioner when it's wound back - pop rivet looks common

 

[mioba]

You will definately fine something to lock of the tensioner, a screwdriver a long allen key, its a very simple design, you will see when you turn it. If you need to replace its not imprtant as the new ones comes with the key

 

[AndySlade]

Small twist drill to hold tension from spring, whilst fitting new belt etc would be my sugggestion, get one closest to hole size.

 

[Blobcat]

Small twist drill to hold tension from spring, whilst fitting new belt etc would be my suggestion, get one closest to hole size.

Problem is access, I can just get my hand down into the gap behind the radiator - I can't tun my hand when it's down there so it will be a case of wind it back with my left hand, "carefully" place something in between my fingers on my right hand then feed it down to the tensioner. I'll then drop that one and never see it again (it will join all the 10mm sockets... ) and repeat it again until I either run out of things to put into the tensioner or I manage to get one in...

 

[Blobcat]

Parts ordered from MB Grangemouth with a very healthy forum discount
£5 for delivery (or free to local Arnold Clarke (I went for the delivery))

Drivers side mirror glass in stock (Pheasant interface on the M1)
Poly Serpentine belt in stock
Idler Pulley wheel in stock in Germany so shouldn't be too long to get

MB Grangemouth parts department an absolute pleasure to deal with, check the part numbers as 2 pulley are listed for the M272, really great customer service.

Did it as a stock order to keep the ££ down so should be here next week sometime, In the meantime I'm slumming it in the 911

 

[LostKiwi]

In the meantime I'm slumming it in the 911

I feel for you. Seriously I do.
Must feel like you're sat in a wedge shaped box with all this sunshine today

 

[Blobcat]

I feel for you. Seriously I do.
Must feel like you're sat in a wedge shaped box with all this sunshine today

I appreciate the forums support in my time of need...

 

[Blobcat]

Bits arrived Friday at work, but I was working from home on Friday so picked them up today.


Breaker bar and 17mm socket to wind off the tensioner. Didn’t bother holding the tensioner off with a pin/rivet etc. Didn’t need to


Quite a lot of the plastic from the idler stuck in the water pump pulley. Managed to get it all out with a screwdriver.
Checked all pulleys and all smooth and spinning nicely.

Had to prise off the back of the old idler from the mounting then clean it up before fitting the new one.
All went together pretty well and access wasn’t as bad as I first thought.
Belt was a bit tedious as twisted from packing. Fed it through then wound the tensioner back and slipped it on.
checked it was in all the right groves then gave it a start.



No untoward noises and all still in the right grooves after switching off.

I think the bearing and belt needed replacing...




Also replaced the drivers door mirror, again not a bad little job.

 

[mioba]

Good job.
Now the car needs a serious wash

 

[Blobcat]

Good job.
Now the car needs a serious wash

I’m thinking more of a “flippant“ wash, but I know what you mean
It will be going through the car wash later this week

 

[Blobcat]

Good job.
Now the car needs a serious wash

 

[mioba]

Thanks for the follow up post.

 

[Blobcat]

Thanks for the follow up post.

Way too many threads go cold and we never know what happened