Rod knock on 2 seperate engines in the same car. What am I doing wrong?
 

Am I doing something wrong, or do I just have bad luck? Last year my 300 CD developed a rod knock after trying to start it cold. I replaced that engine with a good used one last month, and the same thing happened again. I have put less than a hundred miles on this engine in this car. I tried to start the car this morning, and it would crank,but would not run for more than a second. I tested the glow plugs and relay, and found a bad relay. I replaced it and got it started. To get it started, I gave it a little throttle thinking it would help to keep it running. It started to knock right away. Is there a common problem with oil not staying between the bearing and journals? or did I just get an engine that was on it's last leg anyway?
I figured that the glow plug relay might have been the cause of the first engine failure (trying to start it with a little throttle), but I am thinking there must be another reason. Is there something I can do to prevent this from happening in the future? I now have two OM 617 engines with bad rod bearings, and they are getting harder to find. Anyone have any ideas???

Does the knocking stay with a hot engine?

Very unusual, are you sure it was rod knock and not just a bad case of injector nailing? It can be pretty loud. Or valve noise if they have not had their adjustment in a long long time.

Your running veggie right? Is it a two tank system or single tank? And what is your procedure for dewatering, filtering and heating the oil while running?

The first one was quiet at first, but got worse when warmed up. I only drove it about 20 miles after it started knocking. The second one starts knocking right away.

I was running the first engine on a blend when it blew, and the second engine on the fuel left in the tank with some added Dino D. It started and ran fine the few miles I drove it (except for an oil leak). I have 2 other Benz's that have been running the same blend for THOUSANDS of miles, so I doubt the fuel was the problem.

I don't know about injector nailing, but it sounds like a rod knock to me. It started making noise about the second or third time I tried to start it, and was continuous while running.

Have you set your timing, checked your injectors....
Try running it on just regular diesel fuel.... after checking everything...

Did you happen to swap injectors from the old engine to the new one? A faulty injector can cause knocking from strong nailing that you would swear was a rod...try isolating them by cracking the hard lines one by one while it is running and see if the knock stops. If so, then you have found the problem.

Does it go away if you crack open any of the injector lines?

Woops, I see this is a repeat...:o

Where was the oil leak and how much was it leaking?

The engine was running great when I pulled it from the 82 300D that I drove for at least 25 miles after buying it (trans had a shifting problem). I would assume that the timing and injectors are fine. Yes, I will try running it on regular Diesel before pulling it.

I pulled out the bad engine, and put in the complete engine from a drivable 300D (drove it 25 miles after buying the car).

What about that oil leak?

I think from the rear pan or main seal. I cleaned the entire engine at a local car wash before removing and installing it so I could see if/ where there were leaks if any. I knew about the leak right after the swap, so I checked the oil every time I took it out. The level was within the marks when it started making the knocking noise. I also changed the oil and filter before the swap (with the proper 15-40 oil).