I spent hours and hours reading posts on this forum on when to replace the timing chain and it seems like the general opinion is: keep checking the chain for stretch and replace it when stretch reaches about 5 degrees.

However, today I contacted a mechanic who was highly recommended to me as someone who is very knowledgeable on these old MB diesels and this is what he had to say about timing chain replacement: when your car reaches 100,000 miles, just replace the chain. I explained to him that there are a lot of well experienced folks on this board who own several of these vehicles and that they recommended that you simply keep your eyes on the stretch before you decide to replace the chain and he said that it is rubbish . Then when I told him I have just 149,xxx miles on my 1984 300SD he said: since the previous owner didn't change the chain, if I were you I wouldn't be driving that car.... I have seen cars with very nice looking chains break... the only proper way to measure chain stretch is to take the entire chain out and place it right next to a brand new one and then make a comparison.

Let's just say that right now I am COMPLETELY CONFUSED on which way to go! Advise please.

How much money will this guy make changing the chain for you?
What reason would we have to misslead you ?

The factory shop manual says when stretch gets to a certain point put the offset key into the cam sprocket to fix it... like four sizes are available to bring it back to stock... when the offset key can not accomplish that then you need to replace the chain.
Keep in mind that the chains seldom break THEMSELVES.... it is usually lack of upkeep on the chain rails and slides.... they wear through or come off and catch the chain and cause problems....
I think renewing those every 100,000 miles would be good protection... I am not sure if that can be done without removing the chain.... someone will know and should speak up soon.... I assume they can ( at least with small hands ).... LOL

He wants $400 to do it... and that includes the cost of the chain. But I don't know if he included the cost of changing the rails, etc

I understand that no one here would mislead me. This place is full of good people.

He just sounded really cocky about it. What mostly got me super confused is the fact that from reading what's posted here , some folks have MB diesels with 300K miles, 384K miles, etc still running on the original chains and injectors. When I mentioned that to the mechanic he just said, "yeah I've heard those myths too." Now I know these aren't myths, but that just got me confused.

You really do not hear about many chain failures on the 615, 616, 617 series engine, at least not on this board. I suspect that chain failures are predominately caused by infrequent oil changes and generally poor/bad/non-existent maintenance practices. Something that, if you admitted to doing around here, would merit an immediate whack on the hand.

Lilly's chain had 267,000 on it with about 9° of elongation when I replaced it 'on principle', and just to be able to say I'd done it too. FWIW, the banana rail is a gold-plated PITA to get out. After inspecting it, I decided that it wasn't worn enough to warrant changing. IMHO, that particular part must be made from ailen materials found at the Roswell site to withstand 250,000+ miles of operation and exhibit not one whit of appreciable wear.

FWIW, wholesale for the chain is somewhere between $80-$110, the master link is about of bucks and the tensioner and thermostat housing gaskets are another $2-$3.

It's not a hard job (motor mounts are tougher) but is tedious and time consuming. Also, it is imperative that you remove the rail tensioner before rolling in the new chain. Once the chain is in, replace the tensioner and 'reset' according to the FSM's instructions.

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Never a dull moment at Berry Hill Farm.

His motives may not be the issue, it may be a difference of perspective. Since he is a mechanic, if it were his car, he probably would change the chain just for good measure and because it is cheap insurance. I grew up on honda motorcycles and my rule was: keep the chain tight, the valves loose and the oil clean. That idea came to apply to all engines in the many years since.

If you want (think you need) a new chain, change it yourself. I have changed chains in many engines and it is not a bad job, just don't let go of the chain. Keep it (them) wrapped around the sprockets every second of the job and don't let it hang loose.

Cars are more than just transportation to many people, if you would be proud to change your timing chain, do it.

About 2 years ago I nearly bought a 300D, but got to know the new owner thru email discussion about biodiesel.
after a year she asked if I knew anyone with a 300D head for sale. It seems her mechanic recommended she replace the timing chain.
She agreed and he did the job.
A week later, the new chain came off and IIRC. destroyed the cam blocks, valves and there was damage to one piston.

The engine was repaired, but she was without her Merc for about 6 weeks. She sold it when she got it back, because she didn't trust that mechanics work anymore.

My interpretation is that he didn't install the chain joining link correctly when he changed the chain. The joining link pins need to be deformed by using the chain setting tool.

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Tony from West Oz.
Fatmobile 3 84 300D 295kkm Silver grey/Blue int. 2 tank WVO - Recipient of TurboDesel engine.
Josephine '82 300D 390kkm White/Palamino int.
Elizabeth '81 280E, sporting a '79 300D engine.
Lucille '87 W124 300D non-turbo 6 cylinder OM603, Pearl Grey with light grey interior


Various parts cars including 280E, 230C & 300D in various states of disassembly.

As R. Leo said, chains rarely break in the 615, 616, and 617 engines. By the way the chain is the same part # for all 3 engines. I have 335k miles on my 83 300TDT, and I just keep an eye on it. I am anal about oil changes which keeps the wear down. If you see signs of chain stretch, I'd recommend replacement rather than installing the offset keys. Compensating for chain stretch is not their intended purpose. Offset keys are used to bring cam timing back to specs after stock removal from the head during a valve job.

Peter

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Auto Zentral Ltd.

The chains may not break that often, but every year we see a few unlucky friends here that have catastrophies with something breaking in there, most likely a slide. I say most likely because there is so little left to work with after that happens.
I say just change those parts now, much cheaper than the alternative. Besides, after changing the timing chain, with over 330,000 on my 78, it lost that annoying idle miss.
Can't say the same for my 81, but that was the problem with the older beast. BTW, it had 8 deg of stretch.

" Compensating for chain stretch is not their intended purpose. Offset keys are used to bring cam timing back to specs after stock removal from the head during a valve job."

That is completely OPPOSITE of what the Mercedes Factory Shop manual says.......

I'd be willing to bet that guide failure isn't usually the direct result of chain elongation but however, the failure of the tensioner to take up all the slack.

And, I'll bet even more money that there are sufficient warning signs prior to this failure as well (rough uneven idle, poor performance, excessive noise from the chain vault ect.)

Obviously, the tensioner can't do it all but poor maintenance (infrequent oil changes for one) would allow the oil gallery going to the tensioner to eventually gook-up and not pressurize the tensioner (IIRC oil ony flows into the tensioner cavity, not through it). Ultimately, when the chain had elongated enough for the tensioner to move to the next detent, it wouldn't/couldn't and voilá: chain slap, slack and eventually whap, there goes the leading edge of the guide just downwind of the cam sprocket.

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Never a dull moment at Berry Hill Farm.

braverichard, how far off is your cam timing now? If it is not more than 4 degrees you should think seriously about leaving it alone. If it is just a little more you can install an offset key. You can see the condition of 1 upper guide and the tensioning rail when you have the valve cover off. Then you can check your valve clearances and spend your money on good lubrication.

braverichard, I think that mechanic is full of rubbish and he's simply trying to make money. The proper way to go is to check the chain for stretch and inspect the guides and tensioner. Every car will wear its chain at a different rate, and to say that every car needs a timing chain replacement every 100K miles is BS. I know LarryBible went 300K+ miles on one chain and it still had very little stretch at that time. Of course chains do occasionally break, but it's usually caused by something jamming the chain, not by the chain itself. That's why replacing the chain without paying attention to the guides and tensioner is useless.

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2004 VW Jetta TDI (manual)

Past MB's: '96 E300D, '83 240D, '82 300D, '87 300D, '87 420SEL

This mechanic may also be betraying a V-8 gasser background. His advice would be sound were this the M117 or similar vintage engine. The inline 6's though, and the diesels, place far less stress on the chain, and with proper care may well last the life of the car. If you have an engine that requires mechanical valve adjustments you should be in there so frequently that you'd detect dangerous chain stretch long before it can become a problem.

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Tjohn

82 300 SD
77 450 SL (gone)

Again going by the book, Mb allows for about 3 degrees stretch. If there is a problem of power then an offset key can be used, but if the stretch is more you must replace the chain. As I stated earlier the primary reason of the offset key is to correct for stock removal as stated in the section on refacing cylinder head parting surface.

Peter

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Auto Zentral Ltd.

"Mb allows for about 3 degrees stretch. If there is a problem of power then an offset key can be used, but if the stretch is more you must replace the chain. As I stated earlier the primary reason of the offset key is to correct for stock removal as stated in the section on refacing cylinder head parting surface."

NOT TRUE NOT TRUE NOT TRUE.
You have not read the MB factory shop manual.

For you guys with math knowledge but no manuals.... can you imagine the amount which would have to be shaved from a head in order to produce this effect ? LOL... not even close...

The manual says specifically that the offset keys are to correct for chain elongation... and that only when you have used the most offset of them and can not get the engine to specs that you must replace the chain...
I can start copying the manual and posting it... but that should not really be necessary...