Rattling sound from timing chain
 

1990 300SE
Engine 103.981
Chassis 126.024

I am hearing a rattling sound which I perceive to be like the sound of the timing chain rattling against the guides maybe? This noise is heard not just after starting up, but continued to rattle minutes while listening to the motor idle. However, when a friend revved the motor up to maybe 1500 RPMs, the rattling stopped. I tried to locate perhaps a loose piece of plastic as the cause but had no luck in doing so. I have read a few threads in this forum regarding the timing chain being strong on these cars (I only have 125000 miles), but could the tensioner be bad? And if I am going through the process of replacing the tensioner, assuming that is the cause, shouldn't I just go ahead and replace the timing chain and all the guides also?

Thanks in advance,
Michael C.

OK, after letting the engine idle for 30 minutes, the rattling almost goes away completely. Every minute or so I can still hear a faint rattle for a few seconds and then it will stop again. I hope this helps.

Michael C.

it does sound
 

like a tensioner issue.

how is your oil pressure?

tom w

Yeah, if you are going to install a tensioner, I would definitely replace the chains too while it is apart.

Now, about the guides and rails, it is my understanding that replacement requires MUCH more labor, as you have to "dig deeper" into the front of the engine. :confused:


I received a quote of $500 for chain/tensioner replacement, but it went to $1200 when I asked about guides & rails. Unacceptable. :rolleyes:

Good luck!

Hi Beach Benz, yes the timing chain set-up on the M103 engine is usually trouble free. Before you start tearing stuff apart I think you should take a close look at the belt tensioner/damper. When the damper fails it can cause a very noticable rattling noise. Look closely at the damper mount where it attaches to the bracket on the left side of the upper front cover. Sometimes the bushing is visibly worn. If it looks OK try this. While you can hear the rattle, push on the damper with a suitable tool ( wooden hammer handle, large screwdriver). If the damper is causing the rattle, the noise will decrease when you put pressure on it. You'll also feel a heck of a vibration. Good luck.

yeah
 

i wondered about that too, but he was so sure it was the timing chain i didnt mention it.

tom w

AC compressor?
 

OK, after letting the engine idle for 30 minutes, the rattling almost goes away completely. Every minute or so I can still hear a faint rattle for a few seconds and then it will stop again. I hope this helps.

Reading his comment above, I'm wondering if it's the AC compressor cycling?

Thanks everybody for the quick responses and excellent ideas.

Tom w: As far as my oil pressure goes, when idling in park, middle between 1 and 2 mark. When idling at a red light, it reads a little past the 1 mark. Upon any acceleration, the level immediately hits the 3 mark with no problem. I must also add that the oil level was low meaning I could add maybe 3/4 quart to bring to full mark.

ILUVMILS: I will try your suggestion tomorrow and report my findings, thanks.

Richard: I can definitely say it's not the a/c compressor because it is disconnected, but thanks for the input.

86560SEL: I agree, that sounds unacceptable.

Replacing the tensioner is a VERY simple job. Replacing the chain IS A LOT MORE WORK!!! Replacing the chain just for the heck of it doesn't make any sense. If the belt tensioning damper checks out OK, remove the Poly V-Belt and see if the noise goes away.

They all rattle at the damper/bolt location

Do as ILUV suggest.
The place is where bolt#6 goes through Damper #10.
Best time to catch it is at idle, in gear ,w/foot on brake.. have someone do that while you jam a screwdriver in there and you will hear it stop as soon as you apply pressue...
Very Common.http://webwench.net/w123manuals/Service/W124/w124CD1/Program/Engine/103/13-3450.pdf

There is an easy O ring fix in the Archieves...

arthur
 

so if the screwdriver between 6 and 7 stops the noise then it is not a serious problem but can be stopped with an o ring? it is actually harmless?

and it would be the same on my 350sdl?

tom w

Yeah, the upper eye of the damper has a rubber insert and they dry out..causing the bond between the rubber bushing and the metal eye to seperate. When this happen, the damper slides from side to side, causing the rattle..the screwdriver test/trick just takes the slop out by jamming it in the space.
If one takes the bolt out and sandwiches an O ring in between the damper eyelet and the frame [ around the bolt] . it stops the side motion and the problem is permanently solved..
The rubber bushing does not wear out, so the damper still works fine, it just floats in the eye ,,so the O ring stops the lateral movement. I have done tons of them and they have never failed again, so it is not a bandaid fix......
I have a DIY article in the archieves on it somewhere ...

EDIT
Found it,,
http://www.peachparts.com/shopforum/tech-help/26091-all-m104-engine-owners-please-read.html?highlight=ring+rattle

Thanks so much! It was the top eyelet of the damper like you said. I am going to try your O-Ring suggestion this weekend.

This forum rocks!

Michael C.

Very good..
The correct O ring you want is the size of the bushing in the eyelet, not the size of the through bolt.

ILUVMILS: What all is involved when just replacing the tensioner on a V8 W126? I do not have any chain rattles and it does not concern me since it is a double chain, but the "ZZZZRRR" sounds from the front of my engine upon first startup when the oil pressure is going up does have me concerned, as I have been told it could be my tensioner causing that noise. I would not mind changing that, if it were easy/low cost repair.

Thanks for any information.