I have a '82 300sd with 100k on the clock. I am told the timing chain should be replaced by some and other say don't worry about it. My experience with a chain is it makes a racket when it gets badly worn. Is this the case with these chains and should I worry. Will it ever make a noise or just break?

If you browse through posted messages you will see more than one discussion about the timing chain. The general advice is, change it!

MikeB

[This message has been edited by mikeb (edited 10-09-1999).]

If you've been good about changing the oil and oil filter every 3000 miles, you shouldn't have to worry to much about the chain yet. Most of them we see in the shop last about 150K. I would recommend replacement then or before if it does decide to start rattling. One of the biggest problems on the diesel though is chain stretch which throws the timing off enough to kill the power output and fuel economy.

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ASE Master Technician, Lead Technician for Deutsch American Inc. Over 6 years of Import experience-specializing in German Automobiles.

One of the biggest problems on the diesel though is chain stretch which throws the timing off enough to kill the power output and fuel economy.
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And that is reason enough to make the change. They sell off-set cam keys for this,
but the easy and best solution is a new chain. You can buy a repacement w.master link that , hooked to the old chain, threads
through the gears with ease. I use a bungee cord to keep tension on the chain and turn the crank by hand in the running direction.
Any that have done this will tell you it is not a big expensive job. It is also advisable to check the chain tensioner.

A PS to this post.
After changing a chain, a good wear comparison is to hold the new and old chain
from the end on it's side view and see how well the other end supports itself. The worn chain will droop a few inches compared to
one in good condition. This is due to wear in the links that you can't really notice trying to measure the chains. This will really show up if the chain has been cleaned of the remaining oil. If there is
little difference between the two when they are changed and the complaint is chain rattle, this is an indication that the
tensioner should be changed.

I own an 86 420 SEL, can someone tell me what timing chain rattle sounds like exactly and when it occurs the most ? I am having a problem in finding out for my self if the chain is due for a change.

Thanks for all the replys. Keep them coming, I need all the advice I can get. One other question, when the chain gets worn badly does it break or just skip the sproket? The results will be the same but just curious.

Mreid: the result may not be the same. A chain that breaks altogether may very well cause the valves to hit the pistons and cause all kinds of internal engine damage. Not to mention what might happen to all the chain tensioners/rails and the sprockets when that chain lets loose at 3,000RPM. I was just at a reputable foreign car parts shop and they said the chain and tensioner should run you less then $100. And labor should be around 3 or 4 hours. Pretty simple and inexpensive job that could cost you a lot if you neglect it. General consesus it to get it replaced ever 100K.

Greg

Just another question/comment. If the timing goes out as the chain stretches is it not safe to assume that if the power and economy are still right up there (35mpg) then the chain must be in good condition?

To address your last question:
When the timing mark on the crankshaft harmonic balancer is at TDC, { Zero degree mark }, there is also a cam timing mark on the front of the cam. If this mark is lined up right on with it's mark, then the timing has not been affected and the chain is not severly streched. That is where the off-set timing keys I mentioned earlier are used to compensate for chain strech. This is easily seen by simply removing the valve cover and hand turning the engine over in it's normal direction to TDC.
There is still a possibility of chain fatigue on high milage engines without visible strech.

Thanks for the replys. I will take the valve cover off and check things and set the valves at the same time.
This is a wonderful site for a new Mercedes owner. I appreciate all the advice.

MReid:
A 420SEL timing chain is old and dangerous at 100000 miles, we typically recommend replacement at or before then. The chains themselves rarely break but slap around and cause the failure of one of the nylon(plastic) guides in the head and immediately snowballing into big money, read $3500.00 plus. Use a Mercedes only tensioner and change it also along with tensioner rail and upper guides. Typical cost $750.00 or so