My FSM ( for the 617 engine, which is the subject in this thread)says "if timing requires correction install an offset woodruff key or, if the chain is excessively elongated, install a new timing chain" Nowhere could I find a definition of "excessive", but certainly the travel of the chain tensioner will not allow for too much elongation before it reaches end of effective travel. If I understand Leathermang's point correctly, it is that while there are several reasons for valve timing variation, stock removal on the head is strictly limited (ON THIS ENGINE, which is the subject in this thread) and the maximum amount removable to restore flatness wouldn't even affect the valve timing enough to use the smallest offset key (0.7mm, which corresponds to about 4 degrees). Why have the offset keys then? To correct for chain elongation. (ON THIS ENGINE, which is the subject in this thread)

"You are making assumptions and not reading the manual verbatim. No where in the OM617 manual does it say install offset keys until they can't bring timing back to specs"

You are going to force me to load down this thread with pictures of the manual...

In fact it says that specifically.

Please get your FSM out and read ( be sure it is the turbo 617 manual ... and stop referring to TSB's which list other engines and NOT the 617 turbo ) on page 05.8-215/4 F2

Under " Adjustment"
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"If the timing requires correction, install an offset woodruff key or, if the chain is excessively elongated , install a new timing chain. "
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In other words, if you can not correct with an offset key, replace the chain.....

"Statement #2 says keys are available in these sizes, but it doesn't say you can use them to correct chain stretch until you run out of keys."

Ok,,, so somewhere you got the impression that this is a one time shot.... that when the chain stretches after being brought back to reasonable specs by using ( whatever size) woodruff.... that you can not go to the next size and correct it again...
Is that your position ?
If yes, where did you get that impression ?

I am saying that they are saying exactly that... use the keys until you run out of them... then you are forced to replace the chain...

Pete, that is exactly my position... Thanks....

Leathermang,

Reading MB instructions is like interpreting the bible. I have read and reread 05-215, and I must concede that it is ambiguous. Perhaps we need someone to interpret the manual directly from German.

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I guess it matters most if you are an Orthodox MB guy, or a more enlightened follower of MB orthodoxy, or a strict follower of Fundementalist MB teachings that take things quite litterally.


I myself believe the offset keys are to allow for getting a cam to spec with a NEW chain. Due to tolerances, and future machine work. Offset dowels are availible for American cars for the same reason to degree in the cam prperly, they were not intended in that capacity to correct for chain stretch.

Just my $.02

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1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
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"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

That's because nobody would ever bother, it's a miracle to find anyone that's actually replaced a chain on most domestic motors.
I always replace them on something with over 100K miles, though they practicaly never break.

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"I guess it matters most if you are an Orthodox MB guy, or a more enlightened follower of MB orthodoxy, or a strict follower of Fundementalist MB teachings that take things quite litterally.

I myself believe the offset keys are to allow for getting a cam to spec with a NEW chain. Due to tolerances, and future machine work. Offset dowels are availible for American cars for the same reason to degree in the cam prperly, they were not intended in that capacity to correct for chain stretch. " --Boneheadedoctor

Not really..... First off.... it SAYS IT IS FOR CORRECTING CHAIN ELONGATION..... which only happens with wear....

second, we know these guys are frugal....

third... I have experience with CHAINS... and know how STRONG a DOUBLE ROLLER CHAIN IS.....

fourth.... if you make up a diagram with the cam sprockets, the angle the chain runs off to the next item on the engine... and do the trig you will see that it does not make ANY sense to manufacture offset keys in the sizes available for the ' future contingencies' you have mentioned....
SINCE you have the ratcheting tensioner on the back side of the chain load...and the IP is independantly adjustable... so the only thing which will need adjustment by using new parts ( offset keys) is the cam sprocket. If you will do the trig and reread the manual it will be obvious the offset keys are not produced for up to the number of degrees they are just for adjustment for things like head height when installing a new chain.... just does not add up...

Guys, I have again read and reread the microfiche version of the instructions for job # 05-215, and it is now perfectly clear to me that the instructions are very unclear. I believe this is the first time in 30 years that I have seen MB leave a procedure to interpretation. It is sort of like the figure ground principle in the study of art. I can interpret these instructions either way. Leathermang is right about the chains being tough. In fact I just read a TSB on All(some)-Data that MB even strenghened the chains from the originals. So my conclusion is that the chains are tough and don't stretch much so I won't worry about it, and if I do get a streched chain situation, I'm going to change the chain. No sense fooling around with offset keys and have to retime the pump too. Pump timing is critical on diesels for power and smoke and possibly cold weather starting. So I will just roll in a new chain and go with the marks. I won't even fool with the dial indicator unless the head has been surfaced or the block has been decked. Just for *****s and giggles I will check my TDMs today to see if any specs are given in them. I still can't believe MB left something as important as chain stretch up to the individual to decide. Myworld is falling apart.

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Really long thread...Interesting issue.

Let us ask this question...What is the cost of repair on the engine if the timing chain does break?

5 times or 10 times the cost of the chain and installation.


$400 looks like good insurance to replace the chain at 100K miles.

Then lets all go for a good drive!

Good Day to all.

You are really stubborn.... but we are shooting for 5 pages ... so what the heck....

Your position is still not logical. Chains stretch MOST when first installed.... and MB says to check it at a certain number of K's...

So if you are afraid of dial indicators and offset keys then you will be replacing the chain WAY more often than is needed... and since you need to set the injection pump with either procedure you are not saving anything... in fact your labor will be more because you will not be taking advantage of the chain ' wearing in' and slowing down its elongation.... which will lengthen the time between IP settings if you use the offset keys... but will be at the same rate if you roll in a new chain each time...
And since the only accurate way to check the chain elongation is with a dial indicator I still can't figure out how you intend to be safe about when you roll in the ( COSTLY ) new chain.....

Did you drop a magnetic base attached to a dial indicator on your toe or something ? The whole thing can be had for less than $25... and are lots of fun to have to check other things.... it takes about 10 minutes to check the chain stretch with the dial indicator method.... what is the PROBLEM with that ?

LOL

Installtion tip: When rolling in a new chain, you should always verify the IP timing. It should be set a degree or so advanced from normal, so as the chain initially wears over the first 20,000km, the pump will go right into spec where you want it. I find that using the far side of spec (advanced) can give a hair more MPG. That means 14.0 ATDC for OM60x engines (spec is 15.0, +/- 1.0) with the RIV method, and 26.0 BTDC for OM61x engines with the wet/drip methods (spec is 24.0 +/- 1.0). The spec for engines from 1990-up actually changed to 14.0, +0.5, -0.0! I keep mine set around 14.0 (RIV method).

Periodic checking and adjustment(WHEN NECESSARY) of IP timing, valve timing and clearance (dial indicator, feeler gauges, offset keys, wrenches, brain)will provide more benefit in engine longevity and performance at less cost than "fixing" things that ain't broke. You can lead a horse to water, but you can't make him drink.......think!

Amen Pete, I am sure by the time we get to page 5 that we will have convinced him... or battered him into submission.... LOLOLOL

Leathermang,

You can't even count so how are you going to use a dial indicator? We are on page six.

I don't know how old you are, but I'm guessing I was using a dial indicator and installing offset keys when you were still *****ten yellow. I checked my 83 300TDT at 225k and it was on the mark. I'm getting ready to do the 335k service on it. I will check timing then. Heck I'll even hook up my Sun diesel timing light, fire it up and see what the flashes say. I can even rev the engine and see if the advance mechanism is working properly. I've owned hundreds of MBs, but I love this wagon. We just went camping this weekend in the Santa Cruz mountains. We went to Carmel, John Steinbeck's Monteray, and the Santa Cruz boardwalk. The 123 300TDT is perfect. If we take anyone else, I use the two luggage rack bars, and if everyone wants to take a bunch of junk, I install the MB safari rack. LOL

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" If we take anyone else, I use the two luggage rack bars,"
That may be ok in N.California.... but around here the roof would fry them in 15 minutes...

Rick pm'd me about the page count yesterday... I guess the number of posts per page is user controlled..... but I don't remember altering mine....anyway, my screen says we are on the 3rd page.... And I am staying till the BITTER END....

I am sensitive to the " high cost tools" label people have put on the dial indicator...... and the impression that checking the position of the number one valve with one is " A Big Job"..... because so many people have posted those sentiments....

Since I own a nice $15 dial indicator from Enco...and a very pretty $6 one from Harbour Freight I don't consider them expensive tools... of course the people saying those things don't own them... and have only seen the $150 ones in the catalogs....
My magnetic base ( with fine adjustment rod) only cost $18.

And I know the procedure ( since we assume a person already has the valve cover off to set the valves ) is a 10 minute operation.

I hate to leave statements without objections posted because people new to working with machines could be left with the idea that those ( muddying the waters) type statements are true.... depriving them of some really great tools.

I am 55... but clearly you have way more experience and tools than I do... therefor it is even more important that I help correct your interpretation of the manual instructions to coincide with mechanical realities...... .... or at least for the benefit of those watching .....

Why don't you start a new thread and post pictures of your camping trip ? I assume you got your wagon in some of them ?