Timing Chain Input Appreciated
 

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.

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.

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.

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.

read this thread-

http://www.peachparts.com/shopforum/tech-help/310618-another-reason-change-your-timing-chain.html

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.

(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.

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.

Thanks again to all. I am going to have the upper guides done this weekend and leaving the chain and the tensioner to the discretion of the mechanic (encouraging him to use the criteria several of you kindly set out). I'll follow up on the findings and how it goes.

Being that you need to remove the p/s pump, alternator, distributor and cam sprockets to replace the upper guides, it ends up being the bulk of the work. I'm lobbying to change out the chain and tensioner too, since in IMO, it's the easiest part of the job and it would make the job complete.

I didn't realize the guides would require all that; you're probably right. I guess aftermarket tensioner is a bad idea? There is a huge difference in cost on that item.

I would insist upon genuine Mercedes parts for all of this repair no matter how good they say the aftermarket parts are if that is what they try to sell you. It's just not worth the risk.
Just my 2 cents worth.

And a side effect, your idle will be much better with a new chain if yours is streeched excessively

Last time I did guides the distributor stayed in place. BUT this could be an M116 vs M117 issue regarding deck heights. I also just replaced the tensioner rail liner. Unsure if MB still offers the liner for that separate currently.

I would rather a 30 year old, 100k+ OEM tensioner be in my vehicle than some aftermarket BS. Oh wait, that is what I did and now I am creeping on 190k. :)

Swag guide rails are good, I have used them in BMW M30s as well as my OM603 and 617. I would run them again. Iwis are the chains I use.

If you are going to buy the parts then add 20% of your cost to his invoice. Why do you think the mechanic should be screwed out of his mark up?
Anziani

Agreed.

Plus how would the tech offer a warranty? :confused: That is right, they will not.

I thought it only fair to share the rest of this saga, to date, as much as it pains me to tell it (and no it is not a need-a-new-upper-engine bad story but it has been a pain....) The advice on here varied in parts so I guess I can say I followed most of the recommendations. I chose a shop who serviced a 300sdl I recently bought according to the records; the guy I used to use retired. They had no problem with me using my own parts so I got an Iwis chain and MB upper guides and tensioner (all of which was about $500). Before they started they called and quoted $600 for labor, with a disclaimer that, given the age, there could be more for the unexpected (frozen bolt, etc). I said fine. They called back not long after and said the labor would actually be $2300. They mis-gauged it. I told them to put it back together as obviously they had no idea what the job done properly would entail. To their credit they didn't charge me. My small town is 90 miles from them so I had it towed to another primarily european car shop in that same area, who told me they could do the whole thing for $1060 plus tax, and I specifically asked if they'd use MB parts and they said yes (they said their warranty program would not let them use my parts). They did the job, seemingly all was ok, I drive it the 90 miles back home, and when I get to my driveway it is smoking like crazy and there is oil pooled around the front of the right valve cover. Oh, before leaving the shop I again confirmed MB parts were used as $133 for a MB tensioner seemed too cheap. He said "Oh I use a guy who has a lot of new old stock (ie that's how I can get MB that cheap)." Anyway, at least part of the oil problem turned out to be insufficiently tightened valve cover bolts but I now think I have some sort of probably more expensive leak in the rear. BUT IMAGINE MY, um, ANGST, while, in the midst of cleaning oil, I see a Febi ensignia on my tensioner!! And that's where I am. I cannot believe I've got a trunk full of MB parts and now I'm wondering if the whole job has been done with aftermarket parts which I tried SO HARD to avoid.

One question I have is whether that tensioner can simply be removed and the MB tensioner put on. Is it as simple as unbolting one and bolting on the other? If they swear the guides and chain are MB, and I could swap out the tensioner, that might get me to where I was hoping to be - but of course how can I trust whatever they say at this point.

ehm, you can have the Febi tensioner replaced with a genuine MB tensioner by someone who knows what they are doing, either you or a tech familiar with the procedure.

Hopefully, you are confronting the shop that performed the work using aftermarket parts while claiming the parts were genuine MB parts. Always best to have a written contract/proposal that both parties sign so there is no misinterpretation about specific details.

Thanks. I spoke with the mechanic this morning who said it came in a MB box, and that the supplier claimed to have been duped. They are going to replace and make sure the replacement is mb.

As a euro parts guy, I would not be shocked to find a febi part in a MB box at all in 2018. Don't shoot the mechanic or parts guy until you're sure they screwed up, which is always possible.

You should also get that kinda stuff in writing before hand imo, when I write up an invoice for mechanical work at the joint I work for, each line item on the itemized invoice is a PN and it has what brand it is. Sloppy ass lazy shops lump stuff together on the bill often times.

Just an update: I think all this has a happy ending. Got the Febi tensioner replaced with MB, all working well there. The oil leak actually turned out to be a cracked oil filter housing which apparently had a lot of JB weld on it. I had the good fortune to find one from a 560SEC with 34k miles (had to wonder what happened for that car to be parted out?!), and all seems to be well - a month after I started down this road! Thanks again for all the valuable input!