Timing chaim on MB 300E
 

Hi you guys there,

I have Mercedes Benz 300e 86, over 200k miles, still runs good. I am concerned whether previous owner replaced timing chain or not because of car's age. I have tried to look into the engine to find where that chain is located but couldnt see anything except a belt behind the fan. Can someone tell me how much i should expect it to cost to be replaced. If it breaks, how much damage may i have on the engine. Also what is the sign of worn timing chain?. I am asking this because sometimes when i start my car in the morning i hear some sound like tak tak tak,it lasts for around 10 seconds and then everything is ok. Also oil pressure goes up to 3, so that is ok.
Thanks Alex

You have to remove the cam cover to be able to see the chain. You can also see the cam "timing" mark when you remove the cam cover which kinda gives you an indication of the amount of chain stretch. Do you know how often the oil was changed in the past - the chain condition is directly related to the frequency of the oil changes. If there is any doubt - go ahead and have it changed. If you change it yourself you will spend less than $200. When I recently changed it in my 300D I replaced the tensioner at the same time. If you pay an independent to do it my guess would be between $400 and $500. If it breaks the cost will be at least 3x these amounts. Figure the MB dealer will be the most costly.

The parts are relatively inexpensive, but its quite a job to exchange the chain.
If there is no way of defenitely finding out whether or not your chain has been changed, I would most defenitely recommend having it done sooner than later.
If the chain breaks the valves are no longer correcly timed and the pistons will hit and bend the valves, leaving the engine inoperable and making a complete head-rebuilt/valvejob necessary.
You should avoid any abrupt accelerations, thats usually what breaks the chain or stretches it.
The M103 straight six in your car is not really infamous for broken timing chains though, the V8's are though. But at your milage I'd defenitely have it done anyways. Better safe than sorry!
The tack , tack sound indicates that your timing chain tensioner is worn out and does not hold the pressure on the chain.
I would get the parts myself and have a reliable independent do the job. You'll need inner and outer rails, tensioner, clamping lever, chain and a masterlink. Collect the replaced parts though. You can never be too sure.
Good luck and happy motoring.
F.J.

aantonic,

You got some good replies here, but they mostly apply to the diesels and other engines.

The tensioner will typically not indicate problems because of oil pressure because on the M103 it is a ratcheting tensioner. As the chain wears the tensioner ratchets tighter. When you change the chain you MUST push the ratchet plunger all the way through the mechanism and reinsert it from the outer direction to give the system slack and allow it to begin ratcheting again. If you don't do this you can break something when tightening everything up on the new chain.

The chain and associated parts are inexpensive as a previous responder indicated, but replacing it is not too bad. The tough part, until you learn the trick to it, is putting the upper timing cover back in place so that it doesn't leak. It is a chronic leak problem unless you put it in place correctly.

Once the upper timing cover is off, you merely cut a link off the old chain at the very top, temporarily connect the new chain to old and feed it through while turning the crankshaft bolt. This is done with tensioner removed. Once you have it in place, CHECK THE CAM TIMING and then peen the master link carefully in place.

The trick to putting the upper timing cover in place is using the special sealant from MB for the lower U Seal, it will let the cover slide into place without moving the U Seal out of place.

These chains are remarkably long lived given that they are a single row chain. I believe that this is due to the ratcheting tensioner.

My personal belief is that the double row chains on the diesels and in line SOHC single bank engines will last virtually forever if the oil and filter are changed FREQUENTLY. However, the single row chains are beginning to be suspect now that miles are stacking up on lots of these engines. If you look at mplefluer's picture in one of his threads, you will see chain failure picture he has very kindly posted. With nothing more than his picture to look at, I am still not sure whether his chain failure was metal fatique or wear-through. But I just ordered a new chain for my M103 engine that has 198,000 miles with 3,300 mile hot oil and filter changes. His picture and some other statements of failure have changed my theory about single row chain life. I still hold by my thinking as far as double row, single bank engines go.

Hope this is helpful and have a great day,

Another comment in regards to the tensioner - this is applicable to when I replaced the chain/tensioner in the 300D. Upon close inspection of the tensioner "spring" you could see where the edge in about the middle section had been rubbing against the side of the tensioner housing. The spring was about rubbed in half of it diameter thickness in this area. Look for flat spots on the tensioner spring.
Unfortunately, I did not get any pictures of it.

Jim,

I agree with you on the old hydraulic pressure only tensioners. There is good pressure and it's working or if it won't hold pressure it's not getting the job done.

On the ratcheting tensioner, it only needs to hold oil pressure occasionally to see that it is ratcheted out to take up the slack. If it only happens at 70MPH it's enough to push it out if need be.

Have a great day,