Does anybody have the instructions for removing and installing the timing chain tensioner on a OM642? Thanks in advance if you do. Old one is out, new one comes Tuesday via UPS.

Symptoms for replacement: When the engine is cold i.e. below 90* C, there is a rattle from the front of the engine. The rattle goes away after the engine gets up to 100* C and there is no rattle the rest of the day from the front of the enigne as long as the temp is above 100*C. Water temp is the temp mentioned. Pulls like a train when fully hot.

P.S. I have seen the YouTube video by Alex, but some doubt exists. One response to Alex was that the new one is easier to install if the engine is turned counter clockwise a given amount......so if someone has the Mercedes instructions, they might enlighten me. Like will the new one just have to be screwed in to 80nm and that's all? Or do you have to remove a ??pin/something to make it functional? before installation?

Never mind. I got the new tensioner from a Mercedes dealer out east this morning. I followed Alex's YouTube video for the most part. I had to use a 1/2" drive electric torque wrench to undo the 23mm size head on the tensioner. I could not do it by myself using an extension and all my force. Elec torque got it out in a half second.

As for putting it back in.......rocked the front pulley with a wrench back and forth a bit to put slack in the chain, untill the tensioner would go in by hand. Putting it in like Alec did with a extension and socket without putting slack in the chain could possibly result in stripped threads and we don't wanna ever, ever go down that road. Fine threads on the tensioner is why. Thanks Alec? or Alex on YouTube.

 

This video refers to the W164 and not the W166. It may be the same but here is the procedure. WAY easier than it appears to be even in the video. If I had to do it again with the below instructions, I bet I could be done in 30 mins max.

This was on my 2013 GL350

1. Remove engine plastic cover
2. Remove the air filter. Unbuckle the two buckles holding the hose that goes from air filter to engine (they look like lunchbox latches). Unscrew 2x eTorx screws and pull out the air filter towards the front of the car. No need to remove anything, just turn it around at different angles till it comes out.
3. Remove air filter housing. Remove the two T30 screws. The back one is really long and easy to see.. doesn't look like the front one at all.. it's a long silver screw sticking up. Front one is a regular looking screw with a T30 head. Pull air filter housing out. Same as above, no need to remove anything just pull it out. Oh yeah, unplug the air intake hose from the front of it and don't forget to put it back on at the end (VERY easy to forget as it blends into the background...)
4. Reach down at the front left of the engine (just in front of the air filter housing) and feel for a 22MM bolt head. Look at your new one, it looks the same. WIS says cut a wire tie and remove the harness out of the way, I didn't do that at all.. no need.
5. Unscrew the bolt and the tensioner comes out.
6. THE MOST IMPORTANT PART. Get a 27mm wrench on the crankshaft pully and turn the engine backwards (counterclockwise) about 1/8 to 1/4 turn. This loosens the chain so there is slack. Now you can easily put the bolt in with no spring tension.
7. Look at your new tensioner and press on the end. See how it's spring loaded? You will NOT need to push the bolt in against that spring tension if you do this right. Now turn the engine 1/16 or 1/8 FORWARD (opposite direction you turned it before) and try the bolt again. Keep doing this and it will eventually go in like a normal bolt (the threads catch). Turn it slowly and by hand until it is ALL the way in before you use a wrench.. do not cross thread!
8. Another way is get someone else to turn the crank pully back and forth while you hold the bolt in till you feel it drop into the hole and have the threads engage. I did it by myself and did it the way I list in #6 and #7 above and it only takes 2 mins longer.
9. ALSO VERY IMPORTANT. When you start the engine, you'll hear a loud TICK TICK TICK that sounds like the chain came off or something. Don't worry it's just the new tensioner being dry and out of oil. I ran it 1000rpm for 10 seconds and panicked because the sound didn't go away. Restarted 2-3 times and when I ran it at 2000rpm for 5-10 seconds, all the noise went away. Probably the best way is to start and let it idle 30 seconds till it lubricates fully rather than the 2000rpm as I did.

Get an OE tensioner only.. this is a part you don't want failing inside the engine or having to do the job again. They're not that outrageously expensive.

We will see tomorrow morning if the tick that started a few months ago at 170k km (110,000mi) goes away permanently. It was ticking a good 5 seconds after parking the truck 12 hours or more. I suspect it will be gone now.

 

Just a quick update to my post above.

When I replaced the tensioner and started the truck a few times, I didn't drive it after. Just left it in the same spot. Next morning started it and the tick was back just like before I replaced the tensioner!

So I called the dealership and booked an appointment to look at the timing chain, since it's under the extended warranty from the Bluetec settlement. 3 weeks to get an appointment

Later that day I drove the GL around. Not a lot, maybe 5 km (3 miles) and parked it.

Ever since then the tick is GONE at startup. I guess I needed the tensioner to get fully lubricated / full of oil. Running it a maximum of 30 seconds wasn't enough. Driving it was.

So replace your tensioner if you hear this tick... it is really quite easy and totally worth it!

 

I have about 274K miles in mine, I don't get the ticking noise on cold starts in the morning, instead, I get it when the engine is already warm and restarting the car after a few minutes to maybe 30mins after it was off. Could it faulty tensioner present itself this way? I have the replacement part already, but now that I've read you write up, I may on the right path here. Any inputs would be much appreciated.

 

BTW just completed the job and you DO NOT NEED to remove ANY air filter or filter housing the tensioner sits on top of the ALTERNATOR for straightforward access
YOu only need to remove the engine cover and the air intake pipe which feeds air to the filter that all.

 

If you have got the Feild measure done on your ML you can go to the dealership and get your timing chain, guides and pressure switch replaced for free at the Dealership.

 

Replacing the tensioner is pretty simple job, like others said, you need to remove the Passenger's side air housing and 22mm socket wrench. Rotate the crank pulley counter-clockwise just enough (25-30deg) for the chain to slack. The new tensioner torque specs is 80NM (you may need a braker bar to remove the original tensioner).

Now, in my case, as soon as I started the car the rattle was pretty bad, worse than with an old, worn and lose tensioner. I drove it for a couple of miles, hoping that after engine is warmed up that noise would disappear but nope, nothing. Same continuous rattle next morning. Besides I got a MIL (CEL). I am taking my car to the dealer for chain replacement, seems it is stretched a lot, to the point I got camshaft related OBD code (it is my understanding that the cam adjuster can't compensate for the stretch).

I am also under under MB extended warranty from the Bluetec settlement so hopefully I will not be paying a lot ) will keep you all posted.

 

Now I am scratching my head, thinking whether or not I should put the old tensioner back in place, since the dealer will likely see the new tensioner in there. Btw the tensioner is NOT covered by MB Extended warranty, the chain itself is.
What would you guys recommend?

 

Small update: cleaned and re-installed the old tensioner, rattle disappeared but I am still going to have my dealer to look into the timing chain stretch. Another thing is, be VERY careful with the aluminum O-ring (or seal ring or just call it a "washer") that goes between the tensioner and the engine block. Somehow I reinstalled the tensioner having both, old and new seal rings there, so when I torqued down the tensioner, both washers got damaged and I got an oil leak. Luckily I didn't take the car for a ride so the leak was rather minor. Yet I have to clean the garage flooring.. What a luck!

oil leak from under damaged seal-ring