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Mercedes Timing Chain Tensioner Replacement
 
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Pelican Technical Article:

Mercedes Timing Chain Tensioner Replacement

Steve Vernon

Time:

2 hour2 hr

Tab:

$200

Talent:

**

Tools:

E14 Torx, 15mm, 27mm sockets, screwdriver

Applicable Models:

Mercedes-Benz ML320 (1998-03)
Mercedes-Benz W203 (2001-07)

Parts Required:

New timing chain tensioner

Hot Tip:

ALWAYS disconnect the battery before beginning

Performance Gain:

Avoiding catastrophic engine damage

Complementary Modification:

Change serpentine belt

The timing chain tensioner is responsible for keeping the proper tension on you timing chains. It does this by keeping constant pressure on the guide rail. If you are starting to get chain noises from the engine, especially on cold start ups you should inspect or replace the tensioner right away. Failure to maintain constant tension can lead to the timing chain jumping a sprocket and then catastrophic engine failure.

The first step in replacing the timing chain tensioner is to disconnect the battery. You are going to have to remove several components to get to the tensioner including the alternator and you will be working around live electric wires here. If you happen to touch the lead going to the alternator against something, you can cause permanent damage to the electrical system if the battery is hooked up. Be smart here and disconnect it. Please refer to our article on battery replacement for more info.

You will need to remove the two air inlet ducts as well as the front engine cover to get access to the coolant temperature sensor on the front of the engine. Remove each duct by compressing them towards the engine and slipping them off the air inlet. With the ducts off remove the front engine cover. It pulls up and away from the engine. The cover is held on by five clips and will easily come off with hand pressure.

You will need to remove the fan next. Please see our article on removing the fan and then return here.

Next, use an E10 (reverse Torx socket) and driver. Locate the tensioner and using the Torx driver turn the nut on the wheel counter-clockwise 45 degrees. You can now slip the belt off the tensioner. There is a picture below that shows you the routing of the belt that you can use when you reinstall the belt.

You can also lock the tensioner into the open position if you need both hands to install the new belt. Turn the tensioner all the way 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.

The alternator is held to the engine by two bolts. Use an E14 Torx and remove the two bolts. There is a spacer that is pressed in the mount that you may or may not have to press out a little to get the new alternator installed.

Lower the alternator down a little so you can get access to the connections on the back. Unplug the harness, pull the plastic cover off the cable connector and use a 15mm socket to remove the cable.

Now you can slide the alternator out of the engine. You will need to move the auxiliary coolant hose out of the way.

Located on the engine block between the upper mounts for the alternator is the tensioner. Use a 27mm socket and unscrew it. Note: make sure you have the socket flush to the block as it is at an odd angle and you do not want to strip it. The tensioner has almost 2 inches of threads on it so just keep unscrewing until it comes out. There will be a little oil that comes with it so be prepared. Clean around the block and make sure the new seal is on the new tensioner.

Make sure you disconnect the ground terminal (red arrow) from the battery before you begin this project.
Figure 1

Make sure you disconnect the ground terminal (red arrow) from the battery before you begin this project.

You will need to remove the two air inlet ducts (red arrows) as well as the front engine cover (yellow arrow) to get access to the air filter housing on top of the engine.
Figure 2

You will need to remove the two air inlet ducts (red arrows) as well as the front engine cover (yellow arrow) to get access to the air filter housing on top of the engine.

Remove each duct by compressing them towards the engine (red arrow) and slipping them off the air inlet.
Figure 3

Remove each duct by compressing them towards the engine (red arrow) and slipping them off the air inlet.

With the ducts off remove the front engine cover.
Figure 4

With the ducts off remove the front engine cover. It pulls up and away from the engine (yellow arrow).

The cover is held on by five clips (red arrows) and will easily come off with hand pressure.
Figure 5

The cover is held on by five clips (red arrows) and will easily come off with hand pressure. Note: You will need to remove that fan from the car at this point. Please see our article on removing the fan and then return here.

This is a picture that shows you the routing of the V-belt; the tensioner is shown by the red arrow.
Figure 6

This is a picture that shows you the routing of the V-belt; the tensioner is shown by the red arrow. Note: the front of the car has been removed to give you a better view.

Locate the tensioner and using the Torx driver turn it counter-clockwise 45 degrees.
Figure 7

Locate the tensioner and using the Torx driver turn it counter-clockwise 45 degrees. You can now slip the belt off the tensioner and install the new one.

You can also lock the tensioner into the open position if you need both hands to install the new belt.
Figure 8

You can also lock the tensioner into the open position if you need both hands to install the new belt. Turn the tensioner all the way 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.

The alternator is held to the engine by two bolts (red arrows).
Figure 9

The alternator is held to the engine by two bolts (red arrows).

Use an E14 Torx (red arrow) and remove the two bolts.
Figure 10

Use an E14 Torx (red arrow) and remove the two bolts. There is a spacer that is pressed in the mount (green arrow) that you may or may not have to press out a little to get the new alternator installed. The rear nut (yellow arrow) is part of the block and will not fall into the engine compartment when you loosen the bolts.

Lower the alternator down a little so you can get access to the connections on the back.
Figure 11

Lower the alternator down a little so you can get access to the connections on the back. Unplug the harness (yellow arrow), pull the plastic cover off the cable connector (red arrow) and use a 15mm socket to remove the cable.

Now you can slide the alternator out of the engine.
Figure 12

Now you can slide the alternator out of the engine. You do not need to remove the auxiliary coolant hose (red arrow) but you will need to move it out of the way.

Located on the engine block between the upper mounts for the alternator is the tensioner.
Figure 13

Located on the engine block between the upper mounts for the alternator is the tensioner. Use a 27mm socket and unscrew it (red arrow). Note: make sure you have the socket flush to the block as it is at an odd angle and you do not want to strip it.

The tensioner has almost 2 inches of threads on it (red arrow) so just keep unscrewing until it comes out.
Figure 14

The tensioner has almost 2 inches of threads on it (red arrow) so just keep unscrewing until it comes out. There will be a little oil that comes with it so be prepared. Clean around the block and make sure the new seal is on the new tensioner. Installation is the reverse of removal

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Comments and Suggestions:
320 G Comments: Nick 99 CLK 320 there is too much inside pressure on the new timing chain tensioner, and the piston is extended all the way out. When inserting the new tensioner, the piston end touches the chain guide and it seems very difficult to push it in and start any threads at the same time. Is there oil inside the new tensioner in addition to the spring? is there a special installation tool? Thanks
September 11, 2016
  Followup from the Pelican Staff: No special tool or reset procedure. You have to push it in and hold as you screw it in. - Nick at Pelican Parts  
320 G Comments: Does the new tensioner need to be primed? The old tensioner will not screw in as it is fully extended and is hard to start up male & female for for initial insserting
September 5, 2016
  Followup from the Pelican Staff: No special tool or reset procedure. You have to push it in and hold as you screw it in. - Nick at Pelican Parts  
Afaustino Comments: guys, some help needed, I had just replaced the head-gaskets water leaking into oil and now started to re-assembly the engine. mine is a W202 M112 1998 C280. I am willing to use the same tensioner car has roughly 100K kilometers so I believe it to be still good, however I noticed it has to be pre-loaded or re-set to minimum extension for it to be screwed back in place. This tensioner looks not obvious how to do this, any ideas?
August 2, 2016
  Followup from the Pelican Staff: The factory repair info does not mention resetting before installing. It only states reverse steps to install. You should be Ok with just screwing it in and tightening. - Nick at Pelican Parts  
Roland Comments: Hi there I have the same problem with my Mercedes, I have took everything off apart from a bolt that is on the right hand side from the inner side of the timing chain cover, it is bloody difficult to get to that screw, is there a way of doing it without taking the camshaft and the cilynder block off. Unfortunate I don't have a photo to show you at the moment but if requested I'll probably take one. Kind regards if you know anything about this busters bolt
May 19, 2016
  Followup from the Pelican Staff: What vehicle are you working on? I can't comment with a bit more info. - Nick at Pelican Parts  
Ralph Comments: For some reason any comments past September15 aren't loading up. Or is it just me
October 4, 2015
  Followup from the Pelican Staff: Working for me. - Nick at Pelican Parts  
ralph Comments: Hi

I followed these instructions, but after 2 starts the tensioner on the left new has ended up like that. Any ideas?
October 2, 2015
  Followup from the Pelican Staff: You may lack oil pressure to the tensioner. Check engine oil pressure. - Nick at Pelican Parts  
Boo Comments: Do I need to preload the tensioner? Thanks in advance.
September 19, 2015
  Followup from the Pelican Staff: No. - Nick at Pelican Parts  
a william Comments: do we have to set the crank pulley to tdc or anything of that sort
March 24, 2015
  Followup from the Pelican Staff: That would be a good idea, in case something goes wrong. But if you are not rotating the engine over with the tensioner out, should not matter. - Nick at Pelican Parts  
Wolfy Comments: these instructions are for the serpentine belt, NOT the timing chain tensioner
February 7, 2015
  Followup from the Pelican Staff: Not correct.

Check the final few steps. the beginning of the article is how to gain access to the tensioner, the final steps show removing it. - Nick at Pelican Parts
 

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