Rod knock on 2 seperate engines in the same car. What am I doing wrong? - PeachParts Mercedes-Benz Forum

ROLLGUY · #1 04-26-2009, 11:50 PM

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???

Simpler=Better · #2 04-26-2009, 11:54 PM

Does the knocking stay with a hot engine?

pawoSD · #3 04-27-2009, 12:12 AM

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.

DeliveryValve · #4 04-27-2009, 12:16 AM

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?

ROLLGUY · #5 04-27-2009, 12:35 AM

Quote:

Originally Posted by Simpler=Better

Does the knocking stay with a hot engine?

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.

ROLLGUY · #6 04-27-2009, 12:42 AM

Quote:

Originally Posted by DeliveryValve

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?

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.

ROLLGUY · #7 04-27-2009, 12:47 AM

Quote:

Originally Posted by pawoSD

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.

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.

leathermang · #8 04-27-2009, 02:04 AM

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

nhdoc · #9 04-27-2009, 08:00 AM

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.

mplafleur · #10 04-27-2009, 08:33 AM

Quote:

Originally Posted by ROLLGUY

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.

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

Woops, I see this is a repeat...

kerry · #11 04-27-2009, 10:07 AM

Quote:

Originally Posted by ROLLGUY

(except for an oil leak).

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

ROLLGUY · #12 04-28-2009, 12:27 AM

Quote:

Originally Posted by leathermang

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

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.

ROLLGUY · #13 04-28-2009, 12:30 AM

Quote:

Originally Posted by nhdoc

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.

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

kerry · #14 04-28-2009, 12:33 AM

What about that oil leak?

ROLLGUY · #15 04-28-2009, 12:36 AM

Quote:

Originally Posted by kerry

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

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).