Hi,

Today, I was working on my 300SL, 1992 with 62000 miles . I had a noise coming from the front of my 104 engine just above the distributor cap. Not knocking nor something rotational. (Bought the car like that). So after some research here and there, I concluded it must be the timing chain guid in the valve cover. Removed the valve cover to inspect and change the guide. Surprisingly the chain was so loose that the guide came off without even removing the tensioner. I replaced that with the new one. Then removed the tensioner and realized it was jammed and the inner part wouldn't slide out. Replaced the tensioner with an OE one too. Put everything back and started the engine. The noise was gone. What a good feeling and how short it was. As soon as shifted to R and D the noise came back. It is defenitely the same type of noise. It's not as continious as it was before and not present when driving.


Is there any possibility that the new tensioner didn't extend out far enough to push the chain? Is there any installation trick that I missed.

Is there any reason or possibility of the chain has streached in such a low mileage?

If the side guides are gone bad, would the noise come still from the top of the engine or it would be clearly on the sides?

I am going to remove the valve cover and see if the chain is still loose or the tensioner has done its job.

By the way the guide rail that I removed had some surface marks but not that bad at all.

Any comments would be greatly appreciated.

Sean

I had a customer car with an identical problem. It wasn't getting oil into the tensioner. The spring in the tensioner is mainly there as a backup and for when the car is started, normally oil pressure does the whole job. The oil galley was plugged by sealant, removed that and problem was gone. The car was in about 3 different shops before I discovered this.
Gilly

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Thank you so much for the fast reply. In fact I found a small piece of sealant in the old tensioner. I believe you've caught the problem. Could you please give me more direction how to clean the oil path. Can I do it just from the tensioner housing or need more parts to be removed.

Thanks again,
Sean

First the "proper" way to check it, which is going to sound scary and I WAS scared to try it:
Remove the cap of the tensioner, this will be under tight spring tension as you probably know since you replaced it once. On the part that ratchets into the outer housing, you'll need to HOLD that in tight with oh whatever works that's sturdy. I guess a screwdriver or a punch, THEN have someone either start or just crank the engine and see if oil comes out of the tensioner. If not, you've found your problem, the one I did not a single drop came out of that tensioner.
On the one I did, which btw was a 300CE with the 104 like yours, I had to take the front timing cover off, big job. Owner was one happy dude though! Took it to Milwaukee to a dealership with the typical "great German MB mechanic with the German dialect and name". His advice? Motor Honey-type oil treatments, thanks alot Guenther or whatever yer name is. OK was also at 2 well-known European-only repair shops in central WI. Neither had a clue. Would have this chain-rattle noise, it was more noticeable up around 3500 rpm or so. There is a passage in the front cover that goes from the front of the block, through a port in the front cover and into the tensioner bore. The tensioner is designed to allow passage from the bore itself into the tensioner (through an open space in the outer part of the tensioner IIRC, study the tensioner and you'll see what I mean). MORE than likely if this is keeping oil out, as this one did, there is probably quite a bit in the galley somewhere holding the oil back, not just in the cover. But before starting working on the cover, sure find the small oil hole going to the bore and see if you can clear it. Someone probably resealed the timing cover and got a bunch into the galley hole, gotta be careful where you goop that stuff! Let me know if you have any other questions.
Gilly
PS: If you remove that outer cap and no oil comes out, probably found it, but I'd still want to crank the engine with the cap off, but use a tool as I mentioned to simulate the spring tension just to be sure you don't jump time.

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Thanks a million Gilly,
I'll do the test as soon as I find somebody to help me with cranking the engine. Since the inner part only moves in one direction, can I push it further in and supply the pressure? I know this is not the right cure but will it stay in place or will go back over time?
Back to your test, when I removed the inner part from the old tensioner some oil came out but not a whole lot. Few drops only. This confirms your theory I guess that the path is clogged.

Is there any way to rich in the path by some thin wire or so? Is it deep inside the housing or close to the edge? I saw the hole on the tensioner which is just close the washer. I know that timing chain cover removal is a big job. Not that I don't feel confident but I just don't have the place to do it. I take the car to my friend's house and work there. I was looking at the procedure and it seems that it take a good long time to do it.

Is it OK to drive the car the way it is at all or the loose chain can cause further problems?

Sorry to ask so many questions but you are right to the point and I greatly appreciate your comments.

Best regards,
Sean

!

Try not to drive the car at all until you fix this problem, because if the timing chain were to jump or something else fail while it is loose, then the engine could be destroyed or severely damaged.

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1991 MBZ 300E "Benzachino II" @ 165,000 miles
1990 MBZ 500SL "Shoshanna" @ 118,000 miles

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Just another thought on this problem. If the tensioner is operated by oil pressure and the oil pressure normally drops when the RPM drops, could the sound you hear be caused by too low an oil pressure at idle? What does you oil pressure guage show at low RPM?

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Very good point. I don't think that's the cause in my case though. This happens even with cold engine when you first start and the oil pressure reading is high. I will check the numbers and relation between different RPMs and oil pressure readings tomorrow.

Thanks again,
Sean19

I checked the oil preassure readings related to the noise. It is the same when the reading is close to 3 (engine cold) and when the reading is between 1 and 2 with warm engine. This happens in the same RPM around 600.