What’s wrong with my car now?!?!

[Bicykiller]

1982 300D turbo 164k miles started making a rattling sound at higher rpms. Eventually the sound became much louder and became more constant across all rpms and only would briefly stop with the accelerator in just the right position. At idle it sounds like there is sheet metal or plastic in the engine! Noticed no power changes but running the engine sounds super scary!
I assumed it was the timing chain tensioner and replaced that but that didn’t resolve the issue. Engine idles very rough and very loud and there was a particular smell, I can’t describe, I guess burnt rubber but not as bad.

Here’s video of how it runs:

https://vimeo.com/526647287/bc50023a10

Any ideas what could be causing this or what to check next? I’m about to throw this car in the trash haha!

[tyl604]

Might check the rubber buffers under your air cleaner. Maybe one or two have busted loose and the air cleaner housing is rattling. A longer video might help too.

[Bicykiller]

Originally Posted by tyl604

Might check the rubber buffers under your air cleaner. Maybe one or two have busted loose and the air cleaner housing is rattling. A longer video might help too.

Unfortunately, the rattle and sound is FAR MORE violent and louder than the air housing. I replaced those rubber bits with brand new ones from mercedes source, so those are brand new...

I didn't want to run the engine any longer than necessary.

[barry12345]

Lot of possibilities. Cracked flexplates are not unknown. Might want a working mechanic to have a listen.

Prefferably an older mechanic.

[Rogviler]

Obviously the shaking is the main issue, but don't discount the air cleaner rattling. That thing is like 20 pounds and rattled my whole car before I deleted it. Easy to check, just take it off and see if the rattling is still there. Obviously we're just people on the internet with only your description and video to go by, but don't start with the hardest thing first.

[300d 4 ME]

Wow thats a rumble! How's the oil pressure? Any metal flake in the oil? Could be a flex plate. Crank pulley come lose? Does it smoke now?

Hmm, motor mount maybe? These can go flat and make it feel like the engine is coming out through the hood...

Take a peak around the mounts. See if the engine is sitting on the frame metal-metal. I'm thinking at best this is your issue.

[Bicykiller]

As I research further, I’m leaning more towards flex plate damage perhaps caused by a bad motor mount.
I removed the motor mount to perform an oil cooler line swap, maybe I didn’t tighten it enough?
So maybe a few things combined. I tested it with the air box off and no difference.
Is flex plate work ok for the home mechanic or should I cut my loses and just take it in?

[Usaguy]

Originally Posted by Bicykiller

As I research further, I’m leaning more towards flex plate damage perhaps caused by a bad motor mount.
I removed the motor mount to perform an oil cooler line swap, maybe I didn’t tighten it enough?
So maybe a few things combined. I tested it with the air box off and no difference.
Is flex plate work ok for the home mechanic or should I cut my loses and just take it in?

Before pulling the flexplate/transmission/burning through money why not stick a remote inspection camera in the bellhousing and just take a look at it while rotating the engine by hand? (Those inspection cameras are cheap and have many other uses)

Second thing you can do before firing the parts cannon is to do a compression or leakdown test. Since the engine started to shake and make noise then maybe a piston/valve/prechamber went?

[filp]

Originally Posted by christuna

Before pulling the flexplate/transmission/burning through money why not stick a remote inspection camera in the bellhousing and just take a look at it while rotating the engine by hand? (Those inspection cameras are cheap and have many other uses)

Second thing you can do before firing the parts cannon is to do a compression or leakdown test. Since the engine started to shake and make noise then maybe a piston/valve/prechamber went?

Also you can rent a borescope at autozone for free

[Diesel911]

Have you listened around the engine with a Mechanics Stethoscope or even a large Screw Driver or my favorite a 3-4 foot foot length of boom stick with one end on the part I want to listen to and my Ear on the other end.

Be sure to do that to the Vacuum Pump.

[Bicykiller]

Spent some time this weekend and the harsh sound is 100% emanating from the flex plate area.
Motor mounts are in tact but one was slightly loose ( the opposite side of such I worked)
Can rev up a bit and engine smooths out almost perfectly. Waiting for a camera tomorrow and will pop open the window and see how bad it is!

[gregp1962]

Your symptoms sounds exactly like mine were when my motor mounts were bad. It ran like a dream when I fixed the motor mounts.

[Bicykiller]

Well! That was easy to diagnose! (Not so easy to fix, however) Appreciate all the help up to this point!
See the pics but looks like a few flex plate bolts decided to bail and got their heads sheared off in the process! Cracked flex plate too...

Proceeding to remove the transmission now. Good thing the beer fridge is stocked!

[Usaguy]

I wonder if loose bolts were the cause?

It is sometimes easier to remove the whole engine/tranny from the car to do this job. Unless you have a lift.

[Bicykiller]

Originally Posted by christuna

I wonder if loose bolts were the cause?

It is sometimes easier to remove the whole engine/tranny from the car to do this job. Unless you have a lift.

Definitely loose bolts. The 4 that remained in there were not tight at all. AND not even the right bolts!!! The PO (or whomever) used some generic bolts with random sets of washers/lock washers on each!!! No wonder this failed! INSANE what some people do...
I'm kinda furious actually!
I've been removing the tranny today and it's been pretty smooth actually, should have it freed by tomorrow.
Then I'm gonna slide it back so I can make the repairs and extract the 2 bolt bodies that are stuck in there still.