When To Replace Timing Chain
 

Hello Everyone, Recently got a 1981 240d with an unknown service hx of the last 100k miles. Since I'm going to adjust the valves, while I'm in there is there any way to visually inspect the timing chain for condition and possible need for replacement? I'm not ready to do that job yet! Thanks, JEFF

Welcome to the forum Jeff,
If you use the search button you will find lots of good info there including how to set your valves and measure chain stretch.

I actually meant I was not ready for the timing chain job yet. Not too worried about the valve adjustment. Knock on wood.:):) When timing chains fail, do they actually just break or do they stretch first and then break? Thanks

In most cases they stretch, I have not heard of one breaking.
You can get by for quite a while with offset keys before
actually change the chain.

There is no specific miles to replace it at. You must measure the chain elongation to determine if it needs replacement.
http://www.peachparts.com/Wikka/OM617TimingChainStretch

Replacing the chain is pointless if you do not replace the guide rails at the same time.

the tensioners are just as importnat as the chain, but never let anyone ever tell you the chains never breaks. The chain on my uncles snapped

Jack;

Where do you place the woodruff keys on the timing chain/assembly?

John :confused:

come on people... the search button up top works great. type in offset key
or timing chain it's all there over and over.
http://www.peachparts.com/shopforum/showpost.php?p=1402601&postcount=5

Between the camshaft and camshaft sprocket.

Thanks. Are there pics posted anywhere?

John

It's basically impossible for a chain to "snap" of it's own accord. There must be a prior event.........such as the loss of a guide or the tensioning rail.........that precipitates the chain failure.

Not always. Metal does fatigue over time and everything man-made will have production flaws.

You know the old saying, a chain is only as strong as it's weakest link. All it takes is one bad link for the chain to break. Remember the member (Craig?) that happened to find his chain was missing a link bar?

Just to be clear, that was my original oil pump chain at about 300K miles that had worn to the point the one side link had basically just fallen off. Personally, I like to replace the timing chain/guide/etc. at about 200K miles and avoid playing around with offset keys.

can you see if you have a key installed, or must you remove the cam sprocket?

OK, I'll agree that 300K will cause sufficient wear on the pins to create the possibility of a failure and that it should be replaced at that mileage on principle, due to the potential for catstrophe if it fails.

I presume we're talking 300,000 /miles/, yes? I get a bit confused (my own fault) when I see you guys write 300K because being from Canada I just think to myself "oh, 300,000km".

I'm just around 308,000 Km now, so I figure I have a ways left to go before I get /that/ worried about my chain. FWIW, about 192,000 miles.

Correct.

Yep... I agree with Brian on this...


As soon as my 617 hits 300k ( in about 13k) I am sending her off to my mechanic for him to replace it... I do not want to mess with the chain and related stuff.. at all. I will help him but he will be in control

TheDon, me too. I've got a ways to go, but when I hit 300,000 (heck, maybe 250,000) I will have the MB dealer replace my chain. I've read up extensively on doing it myself and while it /looks/ within my abilities, I figure it's like this: if I mess up installing a new chain and destroy my engine, it's my fault and I have to deal with it. If MB messes up, I am inconvenienced and they have to deal with it. I'd rather make it someone else's problem than my own.

Replacing the chain may cost a couple of hundred dollars .... waiting until the rail goes and locks up the chain and cam and bends valves and potentially knocks dents in the top of the pistons.... well, I am not even going to tell you how much that costs.... you can imagine....
I think it is easier to replace the chain ( and accompanying stuff ) than to do the offset key....

Not really, remove the bolt on the cam sprocket, slide it forward, swap keys and slide it back on. You don't even need to take off the chain.

It took me longer to get the valve cover off than to swap the key.

I've posted pics of this before. Search under my name.

Scott

Well, then the question comes up of which offset key you chose to use...
How did you measure the stuff that counts in making that decision ?
That is what I was factoring in....
and if you just roll in the new chain and rails.. then you have a new chain and guide gear.... a comforting thought since it is the stuff which touches the chain which is more likely to cause big problems....

Measure the elongation and pick the key that brings it closest to 0.
Fastlane sells the keys you need and makes choosing the right one simple.
http://catalog.worldpac.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=2BV1A96NK2C20NAG0D&year=1982&make=MB&model=300-DT-001&category=All&part=Camshaft+Woodruff+Key

I'd offer an opinion, though maybe unpopular.

When I first got into these MB Diesels (16 cars ago), I did every maintenance item by the mile. If I went 3001 miles before the oil change, I felt guilty.

Over the years I've become incredibly impressed with the durability. I choose to bring each car up to snuff and then do maintenance as items fail.

For that reason, I've chosen to not worry about the timing chains. But I also have the ability to go 'out back' and grab another engine (two of them waiting for a home right now).

So, instead of getting overworked on exact maintenance, I've grown amazed at the durability of these cars.

-diesel don

You sure make that sound easy and quick...

Why don't you list exactly the process (and tools) that he needs to follow to get that measurement correct right here in this thread ?
No reference to other threads in other words... Just tell him how to do it.

For somebody with the necessary skills, tools and will, it is. If I could do it 5 years ago when I was still a noobie then anyone can do it.

Tell? I'll show. :)
Download the actual offset key guide: http://members.cox.net/lnewcomb99/Documents/CamshaftOffsetKey.zip

This statement by you is the most important concept in this thread.

If a person has doubts about the condition of the chain elongation then they are likely to have doubts about the condition of the more dangerous parts which rub against the chain... what if the prior owner rolled in a new chain 200,000 miles ago but did not replace the rails ?

Then no matter how well you measure and put in the proper offset key your engine is still in danger of calamity ...
and those instructions are not all that clear... lots of discussion in the archives...

All things considered on an old engine in a car you have not owned since it was new... put in a new chain and all the things which contact it ...

The timing chain on my SL was replaced at 110k, apparently they only have a recommended life of 100k on my gasser. I got to see the cracked plastic guides, yikes. This was when the heads were off the block anyway, so kind of a no brainer It seems to be a common cause of engine failure. .

Do diesels have the same plastic guides that can break off into the chain? It was one of the first things I brought up with my indy, but he said that I shouldn't have to worry about it for another 100k or so.

It is a common cause of chain failure.
If the car is new to you it seems a good idea to check the condition of these guides and rails.... if the engine locks up due to this will your indy pay for the damage ? I would take ' shouldn't have to worry' with a grain of salt...
It may be possible to change out these rails without taking the chain out... I seem to remember at least one side being pulled out the space at the top after being released by the pin....and letting the tension off of the ratcheting tensioner...check the FSM ....

No, look at any other mechanical chain drive. Take a bike for example. The chain snaps when the become old. The links get play in them and the pins that hold them together bend or break and a plate pops off. What happens in a double row chain is one link breaks, then the link aside it breaks from bearing all the weight.

Well jaschanks, Considerable usage of internal working parts of engine will demand to change timing chain, though I advice you to clean your engine thoroughly with an engine degreaser first. You will observe that your engine is getting unable to get started which is also a clear indication to change timing chain. Hope this little info helps.

You can't really change the guides on the 603's without pulling the front cover. Nore the 617 if I remember correctly. On the 603 you can just get at the top guide which is pretty pointless because I doubt that would be the one to break.

All you can get without yanking the front cover is the chain, tensioner, and top guide. The lower guide is impossible, and I don't beleive you can get the tensioner slide either.

But inline engines have short pretty simple chains, not like V engines. So they rearly actualy break. Usualy performance drops to the point where you want to change it long before they actualy fail. On the newer engines that I am more familer with, they seem to average 1 degree of stretch every 100k miles with good oil changes. The older 617/616 seem to stretch them more. I wouldn't touch anything without checking the chain for stretch. And since fuel is freaken expensive and I like to keep my diesels running as good as they can if its more than 2-3 degrees out I'd change it. A new chain is cheap, I can roll a new chain on an engine for what two tanks of fuel cost. Those offset keys are band aids to me, I don't fix things that way. I did put an offset key in my $500 throw away SD.:D Beaters get band aids, good cars don't.

Also you can't worry about every little thing, engines fail, more so 20++ year old engines with a ton of miles on them. If you are worried about the chain or guides keep good clean oil in the sump and don't beat the crap out of it doing 5k rpm up shifts.

Don't worry their are no engine problems that Metric Motors and your checkbook cannot fix!:D

:D Well said, Thank You.

603.96 timing case & chain rails
 

Need pointers on timing case removal
(my engine manual does not include
this chapter!)

I've pulled the head (blown gasket) and
want to change out the plastic in the
timing (300K miles on engine.)

Appreciate any help...I know you've got to
pull about all the pullied accessories at a
minimum.

Thanks, and

Cheers,
Richard Whitney