OK, I bought a 300CD from a fellow forum member who was completely honest about the knock in the engine. Honestly, I bought the car to drive for fun while I am working on the 81 N/A and doing the manual conversion. It will also be a second donor for parts should I ever need anything. It has the black interior, the same as the 81 I am working on.

Well, the car arrives (he drove it here, about 4 hours) and there is a slight knock. The odometer shows just over 200k, the clear fuel filter is clean. It SOUNDS like it is coming from the back of the engine. Of course it COULD be coming from the crank but I'm hoping it's somewhere on the top end. It isn't loud but you can hear it. The PO isn't sure where it is and we agree that it could be a number of things. He was honest about the car right out of the gate. Oh, it doesn't like to idle until it's warm. Once it's warm is seems to run fairly smoothly. Not like my 81 or my yellow 82, but not too bad either.

I have an 82 I am using or parts already so this would be a second CD parts car, if I ever need it. Parts for the CD are rare enough that I wanted to hoard some parts if I ever need them. I'll put liability on it and drive it until then, assuming the engine isn't terminal. I COULD drop my other OM617 in it as well. I was going to put it on an engine stand in the garage.

Side note: The guy shows up with a 450SEL 6.9 Euro on a trailer. He was delivering that one too. His wife was driving my 300CD, he was pulling the 450. It needed to be repainted and some work to be a driver but I would love to have had that car! I've never seen a 6.9 in person. That thing was ridiculous. Mercedes went all out when they built that car. I do love the 116 cars.

Where would a guy start looking for the knock? Any suggestions would be appreciated. I know it could be an injector.

I would start by posting a video of it. I'm sure people are going to tell you to adjust the valves and run some Diesel Purge and all the boilerplate, but "knock" means different things to different people. Once everyone knows what it sounds like it'll be a much better starting point.

-Rog

Start the engine and listen with your head under the hood. Then put your head under the car close to the front wheel front then back. If it's in the crankcase it will be quite obvious. If doesn't seem to be in the crankcase have someone rev it a little to be sure.

I've heard several engines with bad rod journals/bearing bad that didn't knock at idle. Seems to me thought, if it were a rod or main bearing problem it would have manifested itself over a four hour drive.

If it doesn't seem to be in the lower portion, crankcase or oil pan, take a small hose put one end in your ear and move the other around the engine. If it gets louder touch a part of the engine with the hose. You'll know when you locate the sound. Of course the engine should be running when you listen to various parts.

I'm not worth carp on these cars so take this all for what it cost you. I'd loosen the injector hard lines one at a time to see if the noise changes. If it's not an injector it still may give you a starting point when you pull the cam cover.



Try to eliminate one thing at a time. Luck!

__________________
84 300SD
85 380SE
83 528e
95 318ic

The OM617 has to be horribly abused to display a rod knock or any lower end engine damage. It is definitely not common.

There are a number of sources that can sound similar to a mechanical engine knock. They include a mis-squirting injector or failing vacuum pump as the most common.

To refine Clemson's approach, I suggest you buy a mechanic's stethoscope from your closest big-box parts store. They are inexpensive at about $10 and are a valuable diagnostic tool for our stone-age diesels. The technique of loosening one injector pipe at a time can also quickly isolate the sound to a specific cylinder if it is injector related.

A great upgrade that decreases knock, reduces smoke, minimizes engine shake, and improves fuel economy & power is a set of well pressured injectors WITH Monark injector nozzles. I had a knocking noise that sounded like something tapping on the firewall with a wrench and a shimmy to my engine and those inexpensive Monark nozzles upgraded my engine right quick and got her idling "quietly" and motionless. Maybe put foam between your air filter housing and engine too. They tend to tap each other often.

X2 on the injector nozzles. I had never driven a new 617 but I imagine that's how they are supposed to sound and run. It's quite even with the hood up. I pop tested my old injectors and found them popping about 300-400 psi below max limit which was still within specifications but the set I balanced at 1975 psi were like magic.

greazzer can install the Monarchs and get them back to you in just a few days. He is the injector man. I did my own because I'm old, had a hundred bucks to burn on a pop tester, nothing else to do and too much time to do it.

__________________
84 300SD
85 380SE
83 528e
95 318ic

The air cleaner IS making a noise but I held that away from the valve cover so it stopped making noise and the remaining noise sounds like something knocking. This was the only thing I have had time to check since it arrived. I'm going to try the injector line trick and see what happens. We just got a hail storm so I'm covered up at the moment but maybe this weekend.