1992 300SL Timing Chain Noise - PeachParts Mercedes-Benz Forum

Sean19 · #1 08-16-2006, 03:29 AM

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

Gilly · #2 08-16-2006, 05:12 AM

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

Sean19 · #3 08-16-2006, 02:51 PM

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

Gilly · #4 08-16-2006, 04:59 PM

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.

Sean19 · #5 08-16-2006, 08:43 PM

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

Rahulio1989300E · #6 08-16-2006, 11:40 PM

!

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.

Sean19 · #7 08-17-2006, 05:19 AM

Thanks for the advice. I'll try not to drive it. Hopefully I 'll get the chance to work on it and follow Gilly's suggested tests.

Gilly · #8 08-17-2006, 07:48 AM

Ahhhhh, I don't know, the guy who's car I worked on, he was driving his all the time like this. Don't know if I'd sweat it too much, you have a new tensioner and spring right?
You'll only get the inner ratcheting piece to go just "so far", to get rid of the noise you'll have to fix it.
You can try and alternate method to clear the passage, sure, can't hurt to try, I know I did but the stuff blocking the oil galley was back on the block side, not in the cover, there was only a little in the cover.
The chain isn't loose enough to jump when the spring is in place, but when you do the test the spring is NOT in place, so that's why you need to hold it in. It's just loose enough to make the noise.
Gilly

Sean19 · #9 08-17-2006, 02:37 PM

Thanks again Gilly. I'll try and post the results. You're great.
Sean

Sean19 · #10 08-19-2006, 04:54 AM

Dear Gilly,

I removed the valve cover again. Surpizingly I found out that the chain was tight. I believe as tight as It should be. There is still a play about 1/16". I have no idea what the spec is. But there was a big difference caompare to when I had the old tensioner. Before I could see about half inch play and I was able to easily slide the chain guide out without removing the tensioner. As I described there is still a similar rattling noise but now it comes only when the car is stopped and it is in R or D and rpm drops to around 500. As soon as the car moves it goes away.
I realized that there was a play in the new rail guide in vertical direction in one of the holes that is actually not round and kind of oval shape. The oval shape is in the direction that the chain moves and I didn't expext any play in another direction. I can feel the play and to me that could be the cause of this remaining noise. Is there any possibility that that shaft is worn out since the guide is some sort of rubber and the shaft is steel?

I think for now I will drive it the way it is and see if it gets worse over time. If I can change those shafts and if it makes sense to you, I'll appreciate if you advice me how and where I can buy them.

Let me know what you think.

Best regards,
Sean

Sean19 · #11 08-23-2006, 04:42 PM

Today I removed the valve cover again after few days and driving the car several times for total of 100 miles. The chain was pretty tight. So I think the tensionner is still doing its job properly. The rattling noise is still there though when car is stopped in D or R and around 600 RPM.

Rick76 · #12 08-23-2006, 07:40 PM

Your remaining noise may be caused by the upper bushing in the fan belt tensioner damper (small shock). These generally make a noise only in drive or reverse. Easy to check and there are many posts on this forum with more info.

Sean19 · #13 08-24-2006, 04:02 AM

Thanks Rick.

The noise is very clearly coming from inside where the top chain guide is under the valve cover. I assume the noise that you mentioned should come from lower and out of the engine where the belt tensioner is. Correct me if I'm wrong. BTW the noise sometimes very rarely shows up when in P. But very very rare. Only if the RPM falls for any reason.

I'll defenitely check it out.

Thanks again,
Sean19

300holst · #14 08-24-2006, 01:07 PM

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?

Sean19 · #15 08-25-2006, 02:59 AM

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