See post #5 in this thread: http://mbca.cartama.net/showthread.php?t=24112

What are the signs that the engine/car was abused?

Timing chain stretch will give you an idea of how often the oil was changed. Using non-synthetic diesel-rated oil and changing at normal intervals of 5k miles, you should find 2 degrees or less of stretch assuming the engine has 160k miles.

An engine stethoscope would be really usefull to narrow down the location of the noise. There are more than a few external things (like air cleaner bracket broken, or totally collapsed engine mounts) that can make a lot of noise. On the OM60x engines, fossilized o-rings on the oil filter stem can cause the engine to make strange and alarming noises.

If you pull the injectors to look at the pre-chambers and check the condition of the pins, the seal rings are a one-time use item so stock up with new ones before you go that route.

If the noise is injector related, it may remain after the injector(s) is fixed because the carbon deposits in the pre-chambers are still there and will affect combustion noises until they are burned out.

Did cracking the injector lines one at a time point to a specific cylinder?

tap tap tapping. . .
 

I have an '83 300 sd with the same sound. My #1 rod bearing disintegrated. To find out if you share the same problem on a different cylinder, drain the oil and drop the oil pan. If you see chunks of bearing metal, not little slivvers, you have a rod bearing that is gone. You can still have good compression until the rod goes through the side of the engine, making it impossible to rebuild. You are a candidate for an engine swap.

Good luck and best wishes.

Paul

Pull the oil filter element.cut it open see if it has metal fragments,there probably will not be any big chunks because of the screen on the oil pump but if you do have a failed rod bearing there will be plenty of ground up metal.Cheaper and easier than pulling the pan.
Don

Nope, I did all the "easy" stuff. Nothing changed that noise. However, I looked for metal pieces during the first oil change, couldn't find any. That is probably due to the fact that the PO had the oil pan off already and removed them. He then used that blue silicon ***** to seal it. (I guess that answers Maxbumpo's question about the abuse, too).

WTF, now I really don't know what to do. I can't rebuild that engine, no garage, no money, no time.

The engine in my 300SD made the EXACT same noise. I tried everything with no results. the video is on youtube somewhere. I decided to yank the engine and swap it for the one in my dad's wrecked SD. once i had the engine out of my SD i saw a metal stamping on the side of the block that said Ecology auto parts. I guess the previous owner forgot to tell me that:mad:. Anyways that engine is sitting outside now. I wonder if i pull the pan if there will be metal debris in it. I think i will do that tomorrow. I will let you know.

I would pull the lower pan and take a look. If nothing there avails then I would just drive as is and keep an eye out for a good used *cheap* engine on CL or local junkyards. Compression tester is only $40 or so. Engine swap is a three day chore. Plenty of threads on it.

I guess that's exactly what I'm going to do. It would be a shame to throw this car out, the body is almost rust free and everything else works just fine.

Another way to confirm a bad bearing would be getting your engine oil tested. On another list a gentleman named Larry Turner, l02turner_at_comcast.net, http://www.youroil.net/, sells the kits and service as well. He offered a discount to that MB list, ask him for the same, I think that it worked out to about $15 per kit.

This thread has my attention as I have a virtually identical sound on an '85 300D w/ 231K miles that I purchased in Aug. Car runs great, lots of power, appears to be burning some oil though I haven't watched closely enough yet to see how many miles/qt. No smoke. Upon cold startup I can hear the exact same metallic hammer noise that airbus posted on youtube. To me it sounds like it comes from low down in the motor where you can hear it more clearly from the oil pan side than the valve cover side. My worry is also a bad crank or rod bearing. Unfortunately I paid $2700 for my ride (perhaps naively believing everyone who says "these motors just get broken in at 250K") and I'm in the process of a front end rebuild so I'm pouring more into it and hoping I don't have to worry about it.

Maybe on the + side for me is that unlike airbus mine goes away once warm and it doesn't make any noise under load. I guess I'll pretend I don't hear it when cold and I'll just drive until I can't.....then face the motor swap or not question only when I have to make the choice.

Good point about dropping the pan and taking a look-see at the next oil change though.

There certainly is hope. Cheap decent engines can be found if you are not in a hurry. These engines do last a long time if properly cared for. Unfortunately the weakest link is oil supply, particularly the oil cooler lines. These are frequently ignored until they pop under speed and the engine goes bye bye. Another weak link is autolite GP's and ignored maintenance on the prechambers.

What is this ignored prechamber maintenance? What needs to be done to them? And if I pull my injectors out, what am I looking for in the prechamber? Carbon deposits that need to be cleaned out?

Sorry for all the questions... :D

Nothing, they are not wear items. Their only real chances of wear/damage are mechanical impact (From a piston, either the wrong PC shim or piston/rod/bearing failure) and melting (from a bad injector spray pattern).

If you are changing your injectors you should look into the PC with a flashlight and make sure the ball is still suspended in the middle.

If you want to clean out the carbon, do an Italian Tuneup.

You should also verify the bottom is intact. They are 100k maintenance items for inspection.

I can't seem to find that on my copy of the service sheet...

What is your source for this?