Hi,
I just purchased a 1991 420sel with 124k mi. Everything indicates the car has been very well taken care of. I have been unable to determine if the timing chain has been replaced, so I guess I have to assume it has not. There is no irregular noise at startup. Generally it runs smooth as silk in fact. But attached are pics (sorry, best I could do by myself). This shows how much play there was when I pressed up with my finger on the chain (please note one pic is chain in resting position), and shows the color of the guides. The guides have an almost imperceptible ridge in them. This is a weekend car (maybe every other) and I'd obviously like to not spend half the price of the car on timing chain and related parts, but of course don't want to trash the engine. Would replacing upper guides and tensioner be a rational choice, or is doing the whole thing the only way to go in you opinion? Thanks as always.

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Do guides ASAP. Those looks like they have been in there since West Germany. Start on driver side, use OEM only. Same with cam cover gaskets, I have had crap luck with after market ones. You will need new little crush washers too for the bolts.

You can just toss in woodruff keys to get the cam timing back, I had to even with a new chain. I am +1/+1 now on mine. Do cam oiler plastic too. Inspect the ICV hoses, they are probably rock hard. At this age and mileage you will need all new top end rubber at some point. All the aforementioned bits should be maybe $150 (not including the intake manifold business)...just the guides, gaskets, etc.

Park it until you do guides. Really. It could be a several thousand dollar mistake.

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I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.[/IMG]

As good rule, you change out the guides when they're "beer bottle brown." I would do all the upper guides, the chain tensioner and the chain. Especially if the car is in good shape and you plan to drive it for years. I've done enough of these to know that when they fail, the car is worthless.

Ive done a ton of these, do the three guide rails, and the tensioner rail with tensioner and chain and it will go 250 k thousand miles before needing a valve job, the chain is done by cutting a link using a guide tool and with sparkplugs removed roll in a new chain connect a link and your done about
5 hour job plus or minus, see how much your timing is off set to tdc and check marks when cam marks align , read your crank when both cams aligned you should be about 5 degrees stretched at your mileage, I would do the work, if not and the guide rail breaks it causes chain to jump a tooth or two and bam bent valves!

Thanks to all for the insight. I don't know if I'm up to that task myself or not; most likely would just suck it up and pay for it. Humor me with this question. I might not put 25k on the car in 5 years. How much assurance would just need upper guides give me?

The end of that was supposed to be 'how much assurance would just doing the upper guides give me' (if the use was going to be that light). Doesn't really get me anywhere because tensioner could go tomorrow? And if doing guides and tensioner then certainly do chain? I think I hear the answers already. But if the guides only approach has any merit for a very low use totally superfluous car, please feel free to make my day ☺

This information was very useful to me.
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Measure the timing chain stretch, and replace it if is 5 degrees or more.

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Prost!

Thank you all! I feel well armed in my decision.

I would replace at least the tensioner, tensioner guide, chain, chain guides and plastic oil sleeves on the oiling tube. There are plenty of threads on this job here on PP. The life expectancy of guides is related to time so wear isn't usually a critical factor.

Use only Mercedes parts and make sure to cover the openings around the chain with rags so you don't drop anything into the timing cover or the oil pan.

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84 300SD
85 380SE
83 528e
95 318ic

read this thread-

Another reason to change your timing chain

don't short cut it, do it right. the way i check is zero the crank, pull both covers off, look at the cam marks. if off, the rotate the crank until the cams line up. check the crank. 5 degrees and below, change the guides. 6 degrees and above, change the chain and tensioner with the guides. the d/s cam can jump 4 teeth before bending valves. i'd do it all. good luck, chuck.

I would not fret on the chain, the guides are the critical mass object. I have seen plenty of 150k-300k junkyard cars that the upper, driver guide let go. Some even took out the valve cover I have seen. This allows the chain to skip a camshaft sprocket tooth (irrelevant of chain elongation) and bends the valves as the timing is so out.

If the cams are late due to chain elongation, just put in woodruff keys. They will still be late with a new chain, I can assure you of this as the lower sprockets are worn. I have yet to see one M116/7 dual row chain car where the chain failed in the yards. Really. Is it prudent? I guess, but you are not driving a single row chain 380.

The tensioner assembly does not just **** the bed, nor the tensioner rail as that rail is metal with that nylon cover. See above, the guides are the killer.

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I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.[/IMG]

(Some have already opined on this above) but any varying opinions on whether you think I’m ‘taking my car’s life in my hands’ if I drive it 90 miles to my trusted mechanic? Car runs like a sewing machine; no noise at startup. 124.5k??? We wouldn’t be having this discussion with most any other car I can think of, but of course we all know that. If we didn’t love em we’d drive Accords with all their boring utilitarianism!

It will probably be ok...drive it easily and don't shut it off...one start and drive it until you get to the mechanic.

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

ehm, if you want to minimize the timing chain replacement cost you should ask your mechanic if you can provide the parts. That way you could avoid paying his mark-up and buy genuine MB parts online at the best available price.

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Fred Hoelzle