How to replace/change idler/belt tensioning pulleys on SLK 230 - Mercedes Benz SLK Forum

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#1 Old 12-29-2014
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Post How to replace/change idler/belt tensioning pulleys on SLK 230

Hello fellow members!
Finally I came up with the problem of idler pulleys. It seems to be a common failure due to bearings. Oh well, 150,000 miles. I can understand that
There is 1 idler pulley and 2 tensioning pulley but I'll refer to them as simply "idler pulleys:.
My description of the problem is posted here:
https://www.slkworld.com/slk-r170-gen...ml#post1793049
Also, some members reported their pulley failures here:
https://www.slkworld.com/slk-r170-gen...r-replace.html
https://www.slkworld.com/slk-r171-gen...ird-there.html

I found a good DIY on Pelican Parts on how to replace idler pulleys and tensioners:
Pelican Technical Article - Mercedes SLK 230 - Replacing Your Belt Tensioner

Update: I managed to replace all my 3 idler pulleys! It's a relatively easy job and took me about an hour for all 3 I must say what a difference it made!!! Really, now I realized where all my whining noises came from! My sweetheart is a lot quieter!!! I would strongly recommend replacing all 3 pulleys and a shock. Well, the shock itself didn't fail internally (at least mine), what failed is the rubber grommet on the shock (or whatever you call it).
The original pulley on the car are made by INA. So I got my parts from RMEurpoean. Same OEM INA pulleys but a lot cheaper than from the dealer ;-)

Tools you would need:
1) 8, 10mm, 15mm sockets
2) CR-V6 Hex bit
3) Torque wrench
4) Possibly a container to drain coolant.
5) Possibly a star bit set (40 bit if I'm not mistaken)

Now, you have two options - you can drain the coolant since if replacing all 3 pulleys we will need to remove radiator fan shroud to access 2 left ones. Or you can be lazy as me and simply disconnect small top hose from the coolant tank and simply plug the hole on the engine with some rubber or I used shooting earplugs .

New pulleys:


Remove
To remove the radiator fan shroud, and coolant tank please see these threads:
https://www.slkworld.com/slk-r170-cla...slk-230-a.html
https://www.slkworld.com/slk-r170-cla...slk-230-a.html
Next, you will need to remove 2 serpentine belts. Please, check this thread:
https://www.slkworld.com/slk-r170-cla...170-230-a.html
Now simply pop the plastic caps on the pulleys with something like a flat-head screwdriver. Be careful of the fragile plastic. Be patient and proceed slowly not to break the caps. Then, use 15mm socket to remove bolts holding right and left tensioning pulleys. If you're replacing a shock absorber, then you will need to undo 2 screws with star socket. Before unscrewing them, you want to secure the tensioning device with a pin (I used small screwdriver that fit the whole).
Here's a picture.

15mm bolt:


Shock absorber:

Shock absorber removed:


Get your new pulleys, put them back in and screw the bolts with 25 Nm of torque.

Two left pulleys:


New idler pulley made by INA in Slovakia (absolutely same as OEM!)

The upper left idler pulley is secured with CR-V6 bit. simply undo the screw, put new pulley back in, put the screw back in, and the plastic cap.



Belt tension released:

Old vs new. Old on the left, new on the right. See the INA writing on both? =)


Again, old vs new by INA

Both pulleys removed:

New pulleys installed:

Serpentine belts are in place:


That was easy, right?! Don't forget to put serpentine/poly-v belt back in, fan shroud and refill the coolant if you drained it!
That's it we're done here! Now my car is a LOT quieter!
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Last edited by JaysonM; 01-11-2015 at 01:12 PM.
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#2 Old 12-29-2014
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Thanks Jayson - in your investigation of the problem, did you happen to find the issue in any engines other than the 230? I'm particularly interested if the 320's have the same issue.

Len
2003 SLK320 40,000 miles - now lives in Tucson with my daughter
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#3 Old 12-29-2014
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We replaced the tensioner on our 230 back in August. It failed at about 135,000 miles. Easy fix and less than $50 I believe, not including the belt it took out.
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#4 Old 01-11-2015
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Originally Posted by sokoloff View Post
Thanks Jayson - in your investigation of the problem, did you happen to find the issue in any engines other than the 230? I'm particularly interested if the 320's have the same issue.
I have updated the thread with pictures and more info
Sokoloff, I didn't find anything about 320. But if you think about it, bearings are mostly mileage related. And the thing that the rubber grommet from my shock absorber simply deteriorated tells me that it could lead to tensioning device play and failure of the pulley. Luckily, I caught it in time! So, I would definitely recommend you check the shock absorber and pulleys for play. Simply remove the serpentine belts and spin the pulley by hand, check for noises while they are spinning, as well as any play.
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#5 Old 01-11-2015
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Thanks Jayson. Those photos are great.
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#6 Old 04-16-2016
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1998 SLK230

My driver's side tensioner was making a horrible awful noise. It was tilted at a 15 degree angle and the belt slid halfway off.

I just removed the old pulley and the bearing is completely gone. The pully was turning on the shaft with no bearing at all for maybe 30 miles.

Do I need to replace the shaft? Or will replacing just the pulley make things right?
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#7 Old 04-16-2016
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Never mind. That chewed-up "shaft" in the photo was actually the inner race of the bearing. I don't know where the outer race and ball bearings went or how long they were gone. The groove you see in the photo was gouged by the bearingless pulley.

I removed the 15mm bolt and the inner race of the bearing. The metal shaft underneath still looks good. I'm going to order the pulley and cross my fingers.
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#8 Old 04-25-2016
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Success!

I decided to replace the works. RMEuropean had the best price on the 2 belts and 2 of the INA pulleys. New-Part had a much better price on one INA pulley. Both vendors shipped immediately; I recommend them both.

Installation was a breeze, as stated here. The photos from this forum of the correct belt routing were a big help.

You do need a 15 mm deep socket, a T40 driver, and an E10 socket.
Harborfreight is your friend for infrequently used tools like those.
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