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.

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Thanx,
Alberta Luthier
1983 300CD ('Stinky')155k miles, 2.47 diff, EGR removed, AAZ injectors with 265 nozzles from Sean,and vogtland lowering springs.
1984 300SD ('Old Blue')150k Klicks from Japan originally, came with rear head rests, no sunroof and never had an EGR

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.

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81 Mercedes 300SD 289k.......SOLD
82 Mercedes 300CD 252k......slow ride

82 mercedes 300 SD...mi Unknown
83 Mercedes 300D ????ksniff..gone too
84 Mercedes 300D 148k........SOLD
85 Mercedes 300TD 386k and holding some one elses project

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.

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 ...

Jack;

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

John

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Certified Registered Nurse Anesthetist (CRNA)
2002 F250 powerstroke with Plantdrive WVO conversion
1983 300SD 190K miles ,sold
2006 E320 CDI

Between the camshaft and camshaft sprocket.

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

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1981 300SD 512k OM603

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?

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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?

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1985 300D - 599,xxxk - blue interior #265 Monark Nozzle, AL129X, 15" Ronals, Gen II Big Brakes hunting
1985 300D - 491,xxxk - in prog-{A-A IC, 3" exhaust, psi\pyro, 28*BTDC, Hella Euros, IP Limiter removal
1985 300TD - 783,xxxk - parts car,used new engine with ALDA cap inplace
1987 Kenworth T-600 8LL 425 CAT Mech. - 6,000,000+k - DEI exhaust wrap, punched through resonators, 1 recent rebuild,

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.

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1984 300D Turbo, 326000 Km, Thistle Green Metallic