'84 300D timing chain

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Diesel Dude - 21 Jul 2005 23:57 GMT

Dear MBZ Gurus:
My '84 300D has 175k miles on it now and I am wondering about the
timing chain. Do the 617.952 engines need to have them replaced, or at
least inspected regularly?
TIA

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T.G. Lambach - 22 Jul 2005 02:19 GMT

Your question is excellent for the valves will hit the pistons if the
chain breaks. Inspect and replace it if necessary. The inspection is
done during a valve adjustment when the cover is off.

Just behind the camshaft's chain sprocket is a thrust collar with a
notch cut into it. The driver's side of the front cam support has a
groove cut into its middle. Turn the engine by the crankshaft (by hand /
wrench) until the notch is aligned with the groove. That is the cam's 00
degrees position.

With the cam at 00 degrees the next step is to read the crankshaft's
angle from its harmonic balancer. Under all the dirt there's a pointer,
slightly to the left of top.

The chain ought to be replaced if the crankshaft's angle is 5 degrees or
more.

It's replaced by cutting the old chain, attaching the new chain and
slowly turning the engine by hand and so pulling the new chain into
place. The chain's tensioner needs to be released so the ends can be
linked together. Both ends need to be kept in tension to ensure the
chain doesn't jump a tooth. The chain also drives the injection pump so
one doesn't want to lose the engine's timing.

Hope this answers the question.

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Martin Joseph - 22 Jul 2005 17:57 GMT

> It's replaced by cutting the old chain, attaching the new chain and
> slowly turning the engine by hand and so pulling the new chain into
> place. The chain's tensioner needs to be released so the ends can be
> linked together. Both ends need to be kept in tension to ensure the
> chain doesn't jump a tooth. The chain also drives the injection pump so
> one doesn't want to lose the engine's timing.

That is a very interesting method... I guess the sprockets don't wear
out in these engines then? usually in my experience the "timing set"
includes the sprockets and the chain, and disassembling the front
timing case is necessary.

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Conrad - 22 Jul 2005 19:20 GMT

>> It's replaced by cutting the old chain, attaching the new chain and
>> slowly turning the engine by hand and so pulling the new chain into
[quoted text clipped - 7 lines]
> includes the sprockets and the chain, and disassembling the front
> timing case is necessary.

I don't buy the "sprockets don't wear" theory - everything wears. In other
engines, replacing the timing chain and sprockets is recommended. Perhaps
in the Benz Diesels, time and experience have shown that to be
unnecessary, but it still gives me the willies. I've seen two types of
timing chain sold for these diesels, one is a complete chain, pressed
together at the factory, and the other is the "master-link" type chain,
which, indeed, is attached at one end to a cut end of the old chain then
cranked through to replace it. I'm sure the "master-link" type chain and
installation will work for a while - I'm just concerned about the
longevity when a new chain is placed onto old (and I promise you, worn)
sprockets.

This subject has some interest to me because I just bought an 84 300D
"Euro" with a thouroughly locked engine (according to the last
owner, it "stopped suddenly on the highway"). I suspect when I have time
to open it up that the timing chain will be the culprit.

So how bout it folks - anyone have any long-term experience with putting
new timing chains on old sprockets on these models?

Cheers,

Conrad

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Diesel Dude - 25 Jul 2005 23:34 GMT

Thanks for the input guys. I'll have a look-see at the chain when the
valve cover comes off for an adjustment and check the crankshaft angle
at that time, next week or thereabouts.
Cheers,
Steve

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