Hi, having a little trouble maybe with my 300 turbo in my Unimog. I have a fair bit of engine rpm frequency vibration to deal with. It vibrates at idle (which I expect) and less pronounced at high rpm. Through the mid range, however, it sounds to my deaf, ignorant ear that it is nailing. I just had the injectors tested by a very experienced retired MB mech, nothing to indicate any problem. He has listened to it run initially and did the injector line crack test. The aft two injectors didn't really effect idle. He has now suggested checking the prechambers next for cracks. How does this effect nailing? Also, what can anyone suggest to be the cause of this? My thoughts are to do a compression test if the prechambers look ok from the top. The engine is new to me so I don't know what it ran like before my swap, it is also relatively hard mounted in the unimog. I did also replace the crank and bottom end bearings. The conrods never came out, but felt tight. The cyclinder walls were good, never had the head off though. Is the hard mounting the cause of my problem, some crazy resonance developing?
Any ideas? TIA PJL

From what RLeo has described to me the MB people thought they needed pretty soft and well designed engine mounts to keep people happy.
I don't think you can do a reasonable job examining the precombustion chambers without taking them out of the head... everyone seems to fear this process but those that have done it say it was easy. Use the slide hammer version of the tool.... which you can make out of an old injector...... or bolt with the correct matching threads.....

Have you set the injection pump timing ? If yes, which method did you use ?

I had initially set the timing using the drip method described from here, but was pushing blue smoke. Recently I borrowed a snap-on pulse sensing adapter for an inductive timing light. It clamps onto the #1 injector line. I found it to be at 20 degrees(I guess my lack of experience), so I advanced it to 24. Now it puts out black smoke when depressing the throttle, and a little harder to start when cold. Nothing has changed the "nailing". I have also adjusted the valves.
The vibration may be self induced since I customized a 240 flywheel (on a lathe) to match the unimog clutch. I statically balanced the flywheel assy with the crank before reassembly.
I need to iron out these bits so I know how much work I need to put into insulating and other methods of drowning out the engine. It's LOUD in the cab.
TIA PJL

Geez, it's a Mog. It's suppossed to be LOUD in the cab!

If you've done all that, the nailing isn't timing. Pull the injectors and get them pop tested. One will be spitting instead of poofing.

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You might want to recheck that. I think the specification is different for the pulse sensor than for the drip method.

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Rick Miley
2014 Tesla Model S
2018 Tesla Model 3
2017 Nissan LEAF
Former MB: 99 E300, 86 190E 2.3, 87 300E, 80 240D, 82 204D Euro
Chain Elongation References

I do not know what engine you have, but the drip method is all together different and you can not use one if the other method is recommend by MB..
Black smoke and poor cold starting is usually a sign of retarded timing..

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I'm not sure if I've misscommunicated in the posts, I have had the injectors tested and cleaned, as removed, they popped and sprayed near perfectly. The gent cleaned them as a matter of process, but nothing was wrong there. As far as the timing goes, I was led to believe blue smoke was retarded, and white was advanced. Besides I had advanced it 4 degrees during the pulse method. The Haynes manual specifies the drip method with the special MB spiggot, I kind of had to fake the spiggot part. I will probably retard the timing slightly to improve starting. The only thing that I can think of is that the drip method sets start of delivery, and the pulse method, well, senses the pulse which would be after the start of delivery, indicating that the timing is retarded, however, slightly. Can anyone verify my theory?
Anyways, is there any method to determine if the IP is providing adequate, or excessive volume of fuel and pressure? As in my original post, we did a line crack test and the aft two cylinders didn't really change their idle when opened. May not be the case when I reinstall the injectors and bleed it. I would like to check everything possible before reassembly to save on consumeable parts.
I have never heard what was confirmed nailing, but, this sounds like one cylinder isn't firing when in the compression stroke. This is most prominent lower to mid rpm with a load on the engine. The vibration tends to confirm this, as if one cylinder is thumping per rpm. However, it tends to be of a hammer and nail type pitch.

I appreciate you guys racking your brains over this, this forum is stuffed full of experience and knowledge.
PJL