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Replacing Your Belt Tensioner
 
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Pelican Technical Article:

Replacing Your Belt Tensioner

Tom Morr

Time:

2 hour2 hr

Tab:

$50 to $100

Talent:

**

Tools:

E8, E10, E12 Torx driver, deep socket 15mm, 5mm 10mm Allen, T40 Torx

Applicable Models:

Mercedes-Benz R170 (1998-04)

Parts Required:

New belt tensioners and belts

Hot Tip:

Don't work on a hot engine

Performance Gain:

Wont leave you stranded at the side of the road

Complementary Modification:

New belt

The Mercedes SLK230K has two belts and two separate belt tensions. One belt is used to run the Kompressor and alternator while the main belt is used to drive the water pump, power steering and other accessories. The belt tensioners provide a constant tension on the belts, which is needed to run all of the engine accessories. Over time the tensioner can fail to maintain the proper tension and the belt will start to slip. If this happens it will usually make a squealing noise. The tensioner can also fail by the bearing wearing out. This will cause the belt to wear unevenly and fray along the edges. You should check your tensioners and belts every six months for wear, cracking, fraying, delaminating and drying out. If the tensioner is loose or you can wiggle it or if your belt shows any of these signs you should replace them. I recommend you always replacing the belts when replacing the tensioner and recommend you buy two belts and always keep an extra one in the car. You don't want to be stranded on the side of the road for the lack of a spare drive belt.

NOTE: The '99 SLK230 has the newer type of tensioner with the self-contained spring, no shock.

While you can replace just the Kompressor belt by itself if you need to remove or replace the main belt you will need to remove the Kompressor belt first.

This article is going to show you how to replace both tensioners. You will need to remove the fan and shroud first. Please see our article on removing your fan and shroud.

First the Kompressor Belt

Let the car cool so you don't have to work around a hot engine. If you forget the routing of the belt don't worry we provide an illustration below.

With the hood open you need an E10 (reverse Torx socket) and driver. Locate the tensioner and using the Torx driver turn the nut on the wheel counter-clockwise. You can now slip the belt off the tensioner.

Next use a deep socket 15mm and remove the tensioner pulley.

There are three E12 Torx bolts holding the tensioner to the engine. Two of them are easy to see and one is partially hidden under the idler pulley. You do not need to lock the tensioner into place to remove it, actually the Kompressor tensioner, unlike the main drive belt tensioner cannot be locked in place. Remove the three bolts and slip the tensioner from the engine.

Take care and note which bolts goes where as one is smaller than the other two.

Main Drive Belt

Take note of the route of the belt or use the handy reference picture below.

Locate the tensioner and using the E10 Torx driver turn the nut on the wheel counter-clockwise. You can now slip the belt off the tensioner.

To remove the tensioner you will need to lock it into the open position. Turn the tensioner wheel counter-clockwise and insert a retaining pin between the rotating part and the tensioner base. If you do not have a retaining pin you can use a 5mm Allen key. It is easier job to install the pin after you have removed the belt as it can be a tight fit getting the pin in while the belt is in the way.

Use a flathead screwdriver and remove the cap on the tensioner pulley. You may want to order a new cap in advance as they are a pretty tight fit and can get ruined when removing them.

Use a deep socket 15mm and remove the nut and pulley from the tensioner.

Remove the upper shock mount using an E12 socket and swing the shock off to the side. Leave the lower bolt alone as you need a special short 10mm Allen to remove it while it is mounted on the engine.

Remove the two E12 bolts from the right side and lower tensioner, and a T40 Torx to remove the upper left bolt.

Underneath the tensioner is a mounting bracket that helps connect the A/C compressor. Remove the one remaining top bolt and loosen the lower two. You will already have removed one of the bolts when you remove the lower tensioner bolt. This will give you enough room to remove the tensioner form the engine.

Use an E12 and 10mm Allen and move the shock to the new tensioner.

Installation is reverse of removal. Don't forget to remove the holding pin from the new tensioner. Take care to make sure the belt is properly seated on all the pulleys, follows the right path.

This photo illustrates the routing of the Kompressor belt
Figure 1

This photo illustrates the routing of the Kompressor belt

Locate the tensioner and using the E10 Torx driver turn the nut on the wheel (red arrow) counter-clockwise.
Figure 2

Locate the tensioner and using the E10 Torx driver turn the nut on the wheel (red arrow) counter-clockwise. You can now slip the belt off the tensioner.

Next use a deep socket 15mm and remove the tensioner pulley (yellow arrow).
Figure 3

Next use a deep socket 15mm and remove the tensioner pulley (yellow arrow).

There are three E12 Torx bolts holding the tensioner to the engine (red arrows).
Figure 4

There are three E12 Torx bolts holding the tensioner to the engine (red arrows). Two of them are easy to see and one is partially hidden under the idler pulley. You do not need to lock the tensioner into place to remove it, actually the Kompressor tensioner, unlike the main drive belt tensioner cannot be locked in place. Remove the three bolts and slip the tensioner from the engine.

This photo illustrates the routing of the main drive belt.
Figure 5

This photo illustrates the routing of the main drive belt.

Locate the tensioner and using the E10 Torx driver turn the nut on the wheel (red arrow) counter-clockwise.
Figure 6

Locate the tensioner and using the E10 Torx driver turn the nut on the wheel (red arrow) counter-clockwise. You can now slip the belt off the tensioner.

To remove the tensioner you will need to lock it into the open position.
Figure 7

To remove the tensioner you will need to lock it into the open position. Turn the tensioner wheel counter-clockwise and insert a retaining pin between the rotating part and the tensioner base (red arrow). If you do not have a retaining pin you can use a 5mm Allen key. It is easier job to install the pin after you have removed the belt as it can be a tight fit getting the pin in while the belt is in the way.

Use a flathead screwdriver and remove the cap on the tensioner pulley (red arrow).
Figure 8

Use a flathead screwdriver and remove the cap on the tensioner pulley (red arrow). You may want to order a new cap in advance as they are a pretty tight fit and can get ruined when removing them.

Use a deep socket 15mm and remove the nut and pulley from the tensioner (red arrow).
Figure 9

Use a deep socket 15mm and remove the nut and pulley from the tensioner (red arrow).

Remove the upper shock mount (red arrow) using an E12 socket and swing the shock off to the side.
Figure 10

Remove the upper shock mount (red arrow) using an E12 socket and swing the shock off to the side. Leave the lower bolt (yellow arrow) alone as you need a special short 10mm Allen to remove it while it is mounted on the engine.

Remove the two E12 bolts from the right side and lower tensioner (red arrows), and a T40 Torx to remove the upper left bolt (yellow arrow).
Figure 11

Remove the two E12 bolts from the right side and lower tensioner (red arrows), and a T40 Torx to remove the upper left bolt (yellow arrow).

Underneath the tensioner is a mounting bracket that helps connect the A/C compressor.
Figure 12

Underneath the tensioner is a mounting bracket that helps connect the A/C compressor. Remove the one remaining top bolt and loosen the lower two (red arrows). You will already have removed one of the bolts when you remove the lower tensioner bolt. This will give you enough room to remove the tensioner form the engine.

Use an E12 (red arrow) and 10mm Allen (yellow arrow) and move the shock to the new tensioner.
Figure 13

Use an E12 (red arrow) and 10mm Allen (yellow arrow) and move the shock to the new tensioner.

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Comments and Suggestions:
Ian Comments: The replacement tensioner and pulley are exactly the same as the old parts. In fact I refitted the old tensioner with the new pulley to see if that helped, still too small! I've searched the internet and found just one other person who encountered the same problem with this model SLK. They were engaged in an online diagnosis/discussion with a Mercedes mechanic. Both parties ended up just walking away. Anyone else encountered this?
November 30, 2016
Ian Comments: I have just replaced the rear power steering tensioner and pulley in my 1998 SLK230, but I can't get the belt back on. I haven't replaced the belt, it's the one that was already on there. I've got the tensioner fully tensioned with a pin inserted in the second pin hole but the belt just seems to be a few centimetres too small. I've checked the routing diagram and that it's sitting correctly on all the other pulleys/wheels, so I just can't work out what the problem is. Any ideas?
November 26, 2016
  Followup from the Pelican Staff: Maybe the new pulley or tensioner is too large? Wrong part. - Nick at Pelican Parts  
Ohio ref Comments: Replaced both belts following your steps. The photos with the yellow highlights made for simple replacements. We had little struggle getting to the bottom but work our way through it. Removable and replacement took about 1 hour. 1998 slk230 new belts and power steering pump.The directions and photos were spot on. Thank you and I look forward to doing more projects on the list
May 25, 2016
  Followup from the Pelican Staff: Thanks for the feedback. Glad we could help.
- Nick at Pelican Parts
 
Bill Comments: Can you give me the # to the bearing on the pulley mounted to the belt tensioner for the alternator/ kompressor
March 27, 2016
  Followup from the Pelican Staff: I’m not the best with part numbers.

Give our parts specialists a call at 1-888-280-7799. They can figure out what part or repair kit you need. - Nick at Pelican Parts
 
Miketzu Comments: Video of the removal and replacement of the tensioner and the belts for the 2002 slk230 would be most excellent, if that could possibly be supplied. Especially the removal and replacement of the alternator belt for the 2002 slk230
March 21, 2016
  Followup from the Pelican Staff:
We don't currently have that tech video. If we get a chance to perform the procedure, we will be sure to document it.

I would grab a repair manual. It will have the procedure, special tools and torque specs.

Give our parts specialists a call at 1-888-280-7799.- Nick at Pelican Parts
 
Jaye Comments: I have a 99 SLK230 and figure 10 belt tensioner shock doesn't exist which also makes figure 9 incorrect. I did get my belt tensioner off with help from some of the other photos thank you and the 99 SLK230 has the newer type of tensioner with self contained spring, no shock.
July 15, 2015
  Followup from the Pelican Staff: Thanks for the additional info. We appreciate it. I will have the article application updated.
- Nick at Pelican Parts
 
sam Comments: Can you identify components/ parts in fig 1 linked by kompressor belt please thx
June 24, 2015
  Followup from the Pelican Staff: the tensioner, ps pump and water pump. - Nick at Pelican Parts  
Bijan Comments: Great pictures and descriptions.
Thanks,
October 17, 2014
  Followup from the Pelican Staff: Thanks for the feedback. Glad we could help.
- Nick at Pelican Parts
 

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