350SDL Strange Timing Chain Noise During Start Up. - Mercedes-Benz Forum
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#1 (permalink) Old 03-26-2012, 10:44 AM
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350SDL Strange Timing Chain Noise During Start Up.

I have been the happy owner of a 1991 350SDL. Has 171K miles on it, original engine, new reconditioned gear box. Engine uses modest amount of oil, nothing outrages.

As of late when I do a cold start in the morning I get a loud metallic clicking sound in the timing chain area of the engine (front of the engine). It only lasts about 30 seconds to a minute and it is gone. Once the engine is even a little bit warm it will not make the same noise. I have had this car serviced by Gian Wayman of the Import Doctor in Hunting Beach CA, for over 6 years. He looks after my red 350SDL as well, and has been able to fix some complicated problems. But this one has us stomped to far. We replaced the timing-chain tensioner, no cigar. Our next move is to open the timing chain cover and have a look, a lot of work. Before we do that any idea out there?

This is obviously something (small) broken but it is more than likely alleviated as soon as oil starts flowing.
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#2 (permalink) Old 03-26-2012, 10:59 AM
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Bad replacement tensioner? Aftermarket ones are crap. Are you sure it's TC? As you know, there can be all sorts of noises with these diesels. How about posting a youtube video with sound?

Chief

Erstwhile 107, 123, 124, 126, 210 owner
Current 107 280SL
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#3 (permalink) Old 03-26-2012, 11:31 AM
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We bought an orginal MB chain tensioner. No, I am not sure it is the Timing Chain, but the noise comes from that general area so it would appear to be TC related.
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#4 (permalink) Old 03-26-2012, 11:38 AM
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+1

Regarding the work done, was only the tensioner replaced, or the rails too. If the chain wasn't replaced, was it because he measured & didn't find any 'stretch' ?

Otherwise, I'm sure you're already well aware of the unique issues that gave the 350 a special place in the W126 pantheon. I haven't a clue what that sounds like.
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#5 (permalink) Old 03-26-2012, 02:30 PM
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The OM603.97 3.5 litre engine is a POS, but the TC's and guides aren't usually a problem on the 603 engine.

If you are sure it is the TC, I would swap in another tensioner first. It is relatively easy to do, and even a used one from a donor should tell you something by comparing the difference btw the two.

Chief

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#6 (permalink) Old 03-26-2012, 03:04 PM
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I am going to check on the rails cause I do not know. I will get a video posted on YouTube if I can of the noise. The chain was NOT replaced, the tensioner can be replaced from the outside as you know. We have not opened up the chain cover so have not measured the chain.

As for the 603 engine, I know it has been much maligned on this and other sites but I have had very good luck with two 350SDL cars. The first one has the noise, and 171K miles, the second has 130K miles and uses virtually no oil either. So from my experience they are great cars. I know others think otherwise.
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#7 (permalink) Old 03-26-2012, 03:12 PM
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You're lucky. But the clock is still ticking.

The 603.96 is a GREAT engine- vast improvement over the 617. Not so the 603.97 (3.5 litre version). Lots of torque, but just not reliable, and way too high a failure rate- probably along the order of >30%. That is absolutely unacceptable, hence it is a piece of sh!t. I own one, and it will soon be so much scrap metal.

The 126 CAR on the other hand, is magnificent.

Chief

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#8 (permalink) Old 03-26-2012, 03:18 PM
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OK, clarifications. We did take off the valve cover and the timing chain is tight as a drum, that part of the rails we could see appear to be fine. As stated before we installed an original MB chain tensioner. What we have not done is take off the chain cover cause it is a load of work and it is not at all clear that the problem will manifest itself when we do. The mechanic suggested that it may possibly be a faulty pressure valve in the oil pump which is supposed to keep oil in the upper part of the engine. The theory is because the valve is leaky it may allow oil to seep out and drain in the sump hence the initial noise which are some metal parts running w/o oil and this happens to sound like it is coming from the timing chain/front area of the engine but it has nothing to do with that particular area.
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#9 (permalink) Old 03-26-2012, 03:33 PM
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SOunds a little sketchy to me. What is your oil pressure gauge reading on start-up?

These oil pumps produce pressure instantly, and I can't imagine the split-second it takes to pressurize the galleries etc to have that effect. Also, there is always (well, on shutdown) a film of oil that forms the essential boundary layer btw the moving parts of your engine, regardless of pressurization.

You're right, the timing cover at the front is a royal pain to remove. I'm still an advocate of swapping in another tensioner before you do anything else.

Get yourself a stethoscope. Check out the water pump, belt tensioner, etc and try to better isolate the noise.

Chief

Erstwhile 107, 123, 124, 126, 210 owner
Current 107 280SL

Last edited by ChiefRider; 03-26-2012 at 05:17 PM.
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#10 (permalink) Old 03-26-2012, 03:37 PM
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Oil presure gauge indicates fine.

Will swap tensioner with my red 350 and see if makes difference.

Stethoscope is good idea.
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