Dave - here is the other thread related to my work on the tensioner:

603 Idler Pully Replacement - Fan Belt

Toknow - you are right about the fan/fan clutch/radiator. I would have lost those components also in my incident, but I still had them off for the test run. With all the belt flapping and slapping that went on, the radiator was not damaged.

The power source for the belt system is the crankshaft. The crankshaft pulley directly pulls the A/C pulley, then the power steering pulley, then the water pump pulley, and then the alternator pulley. The remaining "loose" end is held by the belt tensioner system. So, I should think a seized or "hung" accessory should break the belt or slip, not pull the tensioner out.

But obviously something did break it out of the timing chain cover - and I don't know what.

There is one pretty tight area between the crankshaft pulley and the water pump pulley where the belt loops around the tensioner. The "sides" of the loop pass quite close to each other, smooth sides (vs. ribbed side) facing. If the belt should touch and grab there, that might rip the tensioner out. (I'm just stretching reason, looking for a failure mode.)

Ken300D

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1982 300D at 351K miles
1984 300SD at 217K miles
1987 300D at 370K miles

"The power source for the belt system is the crankshaft. The crankshaft pulley directly pulls the A/C pulley, then the power steering pulley, then the water pump pulley, and then the alternator pulley. The remaining "loose" end is held by the belt tensioner system. So, I should think a seized or "hung" accessory should break the belt or slip, not pull the tensioner out"


I am not sure that I can agree with this. The belt is connected and if there is a resistance from one component, the tensioner mechanism will 'take it'. Means it will absorb the forces within its engineered spring/shock. The tensiner can stay at this exhaustive mode for a while until things back to normal. when these forces are more and the tensiner stays to its limits longer, it has no other way but to transfer these forces to its components or its holding base, the bolt. It might depend on which component is more effective on that, before or after the tensioner on the loop. That is what I think, at least for now, and it imight be better to check all the components to prevent similar event.

My plastic fan blade got chewed up, but is mostly intact. I'll probably replace it though. The odd noise sounded like metallic knocking, almost like valve lifters or vacuum pump that didn't have oil supply yet. It was cold out, about 25F, and the noise stopped after about 2 seconds and everything sounded normal after that, so I didn't think anything was seriously wrong. I am quite familiar with the serp belt tensioner failures, and mine was not failing - good bearing, not cocked, not rough, not leaking, 23kmi old, even had a new spring (I heard of some breaking so I replaced it as preventive maintenance).

Carrameow, thanks for the offer! I'm undecided if I want a used one or if I should get a new one. Was your new cover any different in design, perhaps more reinforcing ribs around the tensioner hole? I'd love to see a photo of old vs the latest version. I'll also post the part number cast into my broken timing cover, I don't recall the full 10 digits offhand. Side question - did you remove the head and oil pan to replace the timing cover? Or did you just slide it in & out with those in place?

Someone else asked about a failed component causing this, or my larger alternator. The answer is 'no' on both counts. All my driven accessories are still rolling smoothly, and if they did lock up, they'd just burn up the belt. And the larger alternator is *less* load than the AC compressor, which was definitely not in use at 25F temps... I think it was just a casting failure, and/or perhaps was overtorqued in the past. (?)

Gsxr have you said anything bad about her recently? Every time I got pissed at mine and threaten to sell it something major broke! Think back maybe she is just getting back at you for something.

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1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200

I got in touch with Phil by E-Mail for a replacement timing chain cover.

The part number he specified was 601 015 06 01.

I received it within a week and it was an MB branded part - much as you might expect for such a (hopefully) limited use casting.

At first glance, I do not see any obvious design change - such as heavier metal or reinforcements at the tensioner mount.

I'll be interested to compare the above part number with what comes off the car - for me that may be awhile. I've had my fill of working on vehicles in a frigid garage - and with the "reserve" fleet I have now it can wait to spring if necessary.

The UK Haynes manual for the W124 cars provides a procedure for removing the timing chain cover without pulling the engine. I can paraphrase it and post if desired. This is a pretty good book for the W124 chassis and I got mine on EBay.

My new theory - cat under the hood.

But no evidence of blood or fur.

Ken300D

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1982 300D at 351K miles
1984 300SD at 217K miles
1987 300D at 370K miles

I had to unbolt the Oil pan. I remember the service CD said that and I doubted it, but you really do, especially to slip the new cover back on. If you dont you will damage the head gasket.
You don't have to remove the Head, but you do have to remove the Valve cover. (You only need to remove the Head to change the long Banana Slide Guide for the Chain.)
I dont know why people say you have to remove the engine. You want to remove the boxy part of the oil pan also. By doing so in conjunction with unbolting the oil pan, you can get your hand in there and remove all the Debris from the Cover failure. There will be ample light and clearance to really get in there and flush things out; by tilting the pan this way and that way, even with the center chassis/engine cross Member there, you will get enough angle to clean things up.
There are two bolts hidden in the cylinder head that go downwards and secure the pan, you get those off when you remove the valve cover. Also there are two bolts that mount the IP with square nuts that come off.
I guess you know why I am glad I still have my 85 300D. I love the 87 300D, its in a separate world above my 85 but i am terrified of it now. Its college tuition time Between that and keeping the 91 Volvo turbo, I think i may sell my 87 300D, the Volvo is simpler and more trustworthy.
I'll send you a photo and part # of the oil cover I have 2nite

GSXR, you mentioned all this happened after some 90 mph test runs?

Just something to consider but I have seen where some alternators have seized (vee belt) after shut down and when after restarting did not turn! In one case, I took a pair of channel locks and with a little force was able to get it to turn freely and it operated properly for a while longer and this situation had presented it's self several more times before I replaced the alternator! I atributed this fault to seized bearings due to dried out lube and bearings worn undersize that fetched up thus locking the shaft. Oddly there was no unusual play to detect!

Is it possible that upon your high rpm runs that you cooked the bearings that may have presented momentary locking, and when you started the engine the tensioner pulled back to full spring load, then released, then back to full tensioner spring load again, maybe several times within the 2 seconds you mentioned making a sound similar to what you describe before a possibly seized alternator finally freed but not before it did the damage?

I suppose this could apply to the A/C comp as well but doubt it could apply to the water pump? Just a thought...........

BB

Ken, the part numbers in the EPC don't match the casting numbers (same as with the cylinder heads). When you get time check the new cover, please let us know what the casting number is, stamped on the front; and also what the differences are (when you eventually start working on it). Oh, I have the Haynes manual too, I'll look at that.

Carrameow, that makes sense - head stays in place but oil pan drops down. Hmmm. I know it can be done with the engine in the car but with the very limited room to work on it, I'm thinking it may be easier to just pull the engine and be able to fix it on an engine stand. And you can't sell the car now that it's all fixed up!

BB, nope, the alternator didn't cause this. It's almost new and spins freely and never makes any noise. Any locked accessory (alternator or otherwise) should never cause this kind of failure - period. Mercedes redesigned the timing cover twice, I really suspect there is a change in the area of the tensioner threaded hole...

and the radiator cowl and that gives you plenty of room! I would hate to see you remove the engine!! (ps you must be very energetic or California sunshine is a great thing) Please do me a favor, take off the fan, radiator and cowl and see how much room there is first!!....

GSXR I know u to be a very smart guy, perhaps you want to remove the engine and do other stuff also, or else tweak the engine...there may be other reasons you are taking the engine out, like you want to make it much better than they way u came upon it, which often drives me too..

I would really be interested in how long it take u to do it and I hope u would post a daily log--boy just thinking about taking out that transmission, the driveshaft, the hood, the exhaust is making me tired...

I'll be interested to know what will be required to pull the crankshaft pulley. I think there is a harmonic balancer that unbolts somehow, but the crank pulley must be pulled. With the radiator out I hope there's room for a puller.

Here's my daily log:

- Thought about repairing the timing chain cover. Dismissed thought.

(Now, just repeat this for the next 90 days.)

Ken 300D

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1982 300D at 351K miles
1984 300SD at 217K miles
1987 300D at 370K miles

You need the flywheel lock tool for starters. I don't think it requires a puller, its just held on by massive torque (200 lb-ft, I think?) on the center bolt. I forget exactly. The harder problem will be torquing the bolt to spec afterwards. I assume you have the factory service manuals, right? If not, send me an email.

Carrameow - yeah, there are other things I'd like to do at the same time, and I'm thinking it might be easier to just pull the engine and save my back - no leaning over and crawling under things for hours on end. From what I see, pulling the engine isn't all that hard - BillyBob even told me you can leave the oil cooler attached, it will come out with the engine! While it's out I can install the Sportline steering box a lot easier, too. Probably change the head gasket again as well. And since the head gasket and oil pan are coming off, I could change rings & bearings. At that point, maybe re-sleeve the block too. Heck, just rebuild the whole engie. (Kidding, guys, kidding... )

I know mine is a different animal with the 617, but pulling the engine/trans was certainly the way to go with my most recent little mishap. Only way to get the upper oil pan off anyway on mine, but so much easier and pleasant to work on. Did a few other things like replaced the front trans seal. What really helped this time (3rd) was I bought 2 huge turnbuckles and attached them to the engine tilter. Now I can get the whole unit @45 degrees or more easy. It wasn't half the job I feared it would be. I'll post pics if anyone is interested.

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'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.

Got a chance to look at the numbers cast into the new timing chain cover this morning.

It has the part number cast into it: 601 015 06 01

And then below that, by itself, there is a numeral " 3 ".

Perhaps that indicates the third version?

Again, at first glance I don't see anything different with the tensioner mounting area - but will know more when the old timing cover comes off and I can look at and measure things. It may indeed be thicker in that area now.

Ken300D

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1982 300D at 351K miles
1984 300SD at 217K miles
1987 300D at 370K miles

Dave, are you sure you want to put that much stress on the crankshaft? Does the manual say to do it that way? I know in the massive thread that is stickied in Tech Help, the pros say to use the special wrench to hold the hub when you loosen and tighten the bolt. So no stress goes to the crankshaft.

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Rick Miley
2014 Tesla Model S
2018 Tesla Model 3
2017 Nissan LEAF
Former MB: 99 E300, 86 190E 2.3, 87 300E, 80 240D, 82 204D Euro
Chain Elongation References