Timeing chain question on 90' 300SE

[80300dbenz]

I have a 1990 300SE, runs great and in pretty good condition for 180,000 miles. I was wondering do these cars have to have thier timeing chains replaced after a some particular point? Another thing is that I put regular unleaded instead of premium, and when im on the feeder getting on the freeway I can hear a pinging sound is that because of the UNLEADED fuel?

THANKS.

[Gilly]

There is no maintenance point for replacing the chain. If you are concerned about it, what needs to be done is the engine is inspected for the amount of chain stretch it has. There is a maximum allowable amount, I think it is measured in degrees of rotation variation from nominal, 3 or 5 degrees come to mind.
On the pinging, try premium and see if it goes away. You can still use regular in that case (I wouldn't) but don't push the engine to the pinging point if you can avoid it. It's not caused by the unleaded, just the low octane.
Gilly

[80300dbenz]

so there is no certain point to when it needs to be replaced? Have you ever heard of any incident that someones chain snapped? should I be concerned about it with 180,000 miles on it.

[softconsult]

Keep changing the oil regularly. The chains run for a very very long time.

Steve

[Gilly]

No, MB doesn't come out and give a mileage that the chain is replaced at, simple as that. "No maintenance interval" is the proper way to state this. Kinda like, oh I don't know, how about the steering wheel? Leave it alllooone.
BUT of course your smart by concerning yourself with it. Sure, they can break, very very rare, especially on the engine in your particular car. BIG problem is that it's rarely the chains "fault". There are guide rails inside the engine that can break, and if they do they can take the chain with it. It's relatively easy to replace the chain itself, but the rails need alot of front-engine disa$$embly. So, what to do? Listen for what is referred to as "the death rattle". This is a rattling noise on first engine start (of the day), lasts for maybe 1 to 5 seconds. Usually this will ONLY require a new chain tensioner (easy easy job). And get it done quick, as this is REALLY bad for the rails, which can drag you down the slippery slope to broken rails, busted chain, timing gears, etc. If you are really really concerned, get the chain checked for stretch, requires the valve cover to be removed, the timing mark for the cams locked in place with a special tool, and record where the timing mark for the crankshaft is, nominal is that the crank indicator is at TDC.
Gilly

[Gilly]

Originally Posted by softconsult

Keep changing the oil regularly. The chains run for a very very long time.

Steve

Right, Steve, good advice BUT it's got 180,000 on it and guessing he's bought it recently?? I also don't want to start another OIL thread, but regular oil changes on these aren't like MOST cars, 5000 miles is plenty enough, I'd go 7000 or 7500 myself it it were mine. Engine does hold 7.5 quarts of oil. Not like a typical car with 4 or 5 quarts.
Gilly

[S-Class Guru]

I have about 180k on my '91 300SE.
I checked the tensioner a year or two ago, and it was only on the 4th "click"
or "groove" out of 10 possible "clicks".
Difficult to explain, but it's a plunger with ridges and a spring. The chain stretches and allows the spring to push the plunger over the next ridge, and then it can't come back. of course you have to remove and disassemble the tensioner to check this - pretty easy though, only problem is you will need to make a small socket-type tool to hold the tensioner threads against the engine securely while you screw it back in against the spring pressure.
imagine trying to screw on a bottle cap with a 50-pound spring under it.

So, is this "click' or "groove" position a reasonably good way to estimate chain stretch? I would assume the factory probably wanted new nominal to be about 3-4, allowing for stretch, but making sure none were too tight initially?

Oh, about the 7.5 qts of oil: my 103 engine calls for 6.5 qts, but is above the fill mark when I drain for 30 minutes and then replace filter and oil with only 6 qts. The light comes on when it drops 1/2 qt, so I assume all is good.

DG

[Gilly]

The only accurate way to determine chain stretch is the method I've already described.
Gilly