Destroyed Aluminum Threads (and how did I?)

Those are regular tap size. STI seems to be not available in 18x1.5, the tap would be larger. Time Serts are fine but yes you will need to make room to use it.
 
Quite a job to remove that cover.

I’m in disbelief that I screwed this up so bad. Completely disgusted.

Had the pulley bolt not sheared off (not sure why that happened in like 1-4 mile of use), it would be in there, installed, no issues that I’d know. And good to go another 200k.

To add insult to injury. The broken screw could be removed with my fingernail backing it out.

Ugh.

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It is not your fault, I am almost positive it happened removing it and could have happened to anyone.
 
It is not your fault, I am almost positive it happened removing it and could have happened to anyone.
Agreed.

Way ahead is murky. I’ve got a right angle drill for jobs like this. You’ve got enough room to do the drilling, the TimeSert and Helicoil bits are short.

But I wouldn’t want the chips from drilling to get on the timing chain or in the pan. Some guys use grease in the flutes of the drill to catch the chips. I wouldn’t be happy with that.

I‘m leaning towards pulling the timing cover. Looks like the oil pan has to come off to accomplish that. Might have to remove the head. What does the Mercedes FSM say about removing that timing cover?
 
The Steel and Aluminum and I am not sure if I am using the proper term [I am sure one of our A&Ps will let us know ] Galvanic corrode together. I looked at your post before and knew that would happen . Time for a Timsert or Helicoil. Aluminum sucks for that. I have found that on some Aluminum you can just use the tap with out drilling for the Helicoil .
 
The Steel and Aluminum and I am not sure if I am using the proper term [I am sure one of our A&Ps will let us know ] Galvanic corrode together. I looked at your post before and knew that would happen . Time for a Timsert or Helicoil. Aluminum sucks for that. I have found that on some Aluminum you can just use the tap with out drilling for the Helicoil .
The threads were fine when I pulled the old one. I looked them over, went through each one, etc.

There was oil on the threads when I pulled the old one. No signs of galvanic corrosion.

The little shards came out when I removed the new one.
 
Agreed.

Way ahead is murky. I’ve got a right angle drill for jobs like this. You’ve got enough room to do the drilling, the TimeSert and Helicoil bits are short.

But I wouldn’t want the chips from drilling to get on the timing chain or in the pan. Some guys use grease in the flutes of the drill to catch the chips. I wouldn’t be happy with that.

I‘m leaning towards pulling the timing cover. Looks like the oil pan has to come off to accomplish that. Might have to remove the head. What does the Mercedes FSM say about removing that timing cover?
FSM prerequisites are posted above. No head or oil pan (fortunately, since then it would be an engine lift too).

I’m inclined to consider the helicoil or time sert. The prices are high. But I can remove the radiator and condenser and get a straight shot.

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I was thinking about the chips going down.

Often one uses grease to catch chips. I’m thinking maybe I can pack the rear of the hole with either electricians duct seal, grease, etc. even a piece of tape. Then drill, cut threads, etc.

My thought is if perhaps the insert is shorter than the overall threaded depth, maybe I can keep the back of the hole closed off, since it is already more than half occluded.

After all that, wipe/clean, vacuum, flush with fresh oil significantly, change the oil immediately, and go from there.

SMH.
 
The sttel and aluminum corrode together. I has been too long of a time mentally to be precise and proper with a definition and I may be wrong with the facts but the will be generally ball park? some what maybe correct hopefully. The steel and aluminum make a battery and the Aluminum being less nobel loses molecules over time and weakens.
 
FSM prerequisites are posted above. No head or oil pan (fortunately, since then it would be an engine lift too).

I’m inclined to consider the helicoil or time sert. The prices are high. But I can remove the radiator and condenser and get a straight shot.

View attachment 120762

I was thinking about the chips going down.

Often one uses grease to catch chips. I’m thinking maybe I can pack the rear of the hole with either electricians duct seal, grease, etc. even a piece of tape. Then drill, cut threads, etc.

My thought is if perhaps the insert is shorter than the overall threaded depth, maybe I can keep the back of the hole closed off, since it is already more than half occluded.

After all that, wipe/clean, vacuum, flush with fresh oil significantly, change the oil immediately, and go from there.

SMH.
That may be the way to go.
 
I’ve ordered directly from TimeSert - directly from the company. They weren’t quite that expensive, though. Might try seeing what the price is when ordering directly.
 
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As said last thread "steel/alu ionic response/carosion". I think that weakened the frnt portion of threds. Not ur fault.
Decision tree: right angle drill (go/no go). No? remove frnt dress/components & drill 'straight' (go/no go). No? new cover.

I use a bar w/legs mounted to fenders @ hood line, engine fingers that go dwn frm it to hold motor weight. Better alternative than the engine crane mentioned. MB hasa solid pan? jack frm below is good alternative too. My choice? New cover.
 
If you're gonna tackle this in place (and I probably would), don't be afraid to modify tooling as needed. For example, the provided bit appears to be a S&D (reduced shank). If you need to lop some off that shank to shorten the OAL, do it. You're just drilling aluminum and you only need enough length for the jaws of your drill chuck.

I'd probably use grease to try to capture chips, too, but what about getting really fancy and trying for a few lbs of positive pressure in the engine? Can you tap in somewhere with a regulated air line and gently pressurize the timing cover?
 
The sttel and aluminum corrode together. I has been too long of a time mentally to be precise and proper with a definition and I may be wrong with the facts but the will be generally ball park? some what maybe correct hopefully. The steel and aluminum make a battery and the Aluminum being less nobel loses molecules over time and weakens.
I understand what you’re saying, am Im not looking to argue with you. But the original one was not seized in there. Once I used a slightly longer breaker bar, it came right out.

My other thread was written in an abundance of caution, really simple as that.

When I pulled the new one, it too didn’t remove with my shorter ratchet. It’s really just a virtue of being torqued to 73ft-lb with loctite.

When I pulled the old one, threads on the male and female parts were all great. They had oil in them. No dust, no debris, no shavings. I ran a soft pick through them and they were all fine and sharp. No corrosion. M

When I pulled the new tensioner the second time, there was a lot of powder and grit in the threads, and a shard came out.

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Obviously the new one didn’t galvanically corrode in a few hours. The aluminum maybe galled. Henkel claims Omnifit 100M and Loctite 243 are functionally the same. I primed it and there was product there. Unless one of these damaged the aluminum, Im not sure there was any chemically relevant issues.

So Im not interested in arguing galvanic corrosion. I need to figure out the resolution for this situation, and how to avoid it in the future.
 
I think the damage was from the tensioner vibrating as it came loose.Thats what caused the powdery looking front threads. The oscillations from being loose mangled the threads.

Why did it get loose? Hard to say. Did the thread lock have time to set ? Was there something that kept the part from being torqued properly? Is the torque wrench correct ? I'd lean on the side of the fastener was not tight enough, and vibrated loose , then being loose, it ate up the threads.

I'm assuming the threads on both pieces were cleaned. But if a shard or some old thread lock was there, perhaps it caused more torque to be needed for the threads to be tight, the wrench clicked off, and the threads themselves were not tight?
 
When dealing with aluminum threaded parts, you don't have to do anything wrong. A little corrosion or the prescribed loctite may be enough to distort the threads.
I'd try a retap first, especially if you can start the tool from the back side of the casting.
 
Is replacing that timing chain cover an option?
Posssibly. And a lot of work, and time that I don’t really have.

That’s the problem for the hobbyist, right? The time/money/patience/quality type trades.

The timing cover as of now doesn’t leak. Removing it would take more time, more chance for other things to go wrong, etc.

My biggest issue is the trade on family time. My AR side would say to replace it and do it 110% right. My realistic side says the years are short with my three kids, and if the trade is a few hours to pull a radiator and time sert/helicoil it, versus what will amount to far more hours and days in the garage to pull the timing cover, that’s bedtimes and weekends lost on a hobby over my kids. I’m not interested in that. The 350SD is one of the rarer S class w126 cars. It’s a nice car…. I’m into it. But between other fish to fry and family/work, I need to control my AR tendency and get a suitable repair for a 200k mile non-DD.

If you're gonna tackle this in place (and I probably would), don't be afraid to modify tooling as needed. For example, the provided bit appears to be a S&D (reduced shank). If you need to lop some off that shank to shorten the OAL, do it. You're just drilling aluminum and you only need enough length for the jaws of your drill chuck.

I'd probably use grease to try to capture chips, too, but what about getting really fancy and trying for a few lbs of positive pressure in the engine? Can you tap in somewhere with a regulated air line and gently pressurize the timing cover?

This is great perspective, thanks very much!
 
I think the damage was from the tensioner vibrating as it came loose.Thats what caused the powdery looking front threads. The oscillations from being loose mangled the threads.

Why did it get loose? Hard to say. Did the thread lock have time to set ? Was there something that kept the part from being torqued properly? Is the torque wrench correct ? I'd lean on the side of the fastener was not tight enough, and vibrated loose , then being loose, it ate up the threads.

I'm assuming the threads on both pieces were cleaned. But if a shard or some old thread lock was there, perhaps it caused more torque to be needed for the threads to be tight, the wrench clicked off, and the threads themselves were not tight?
The tensioner wasn’t loose. The pulley on it was connected with a bolt that sheared. Was that on me? Something else? I don’t really know. I’ve done quite a few pulley replacements without issue. Something else may be misaligned on this one… I’m starting to get that feeling TBH.

The threads were fully cleaned. Brake cleaner, swabbing down, running through them with a soft “pick”, etc. I used loctite primer and the 243. Both require cleanliness. So I had to clean multiple times before doing the install. The new tensioner torqued down fine and was consistent to remove as compared to the original. Backed out easily. It went until I tried to put it back in that I faced the issue.
 
Possibly started it cockeyed? If its really only the first few threads run an 18mm spark plug chaser down it they are that size. If you do get it in do not torque it to 100nm go about 80 nm, it is not an issue.
 
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