I pull my injectors this morning and took them to the bosh diesel shop. well all my injectors were fine. the spray patterns, and the pop pressure were ok. two of the injectors were at 138 bar, one was at 136, and the rest at 135.

I knew then that the injectors were not causing the nailing problem on the om 606.962. I explain to the mechanic what i am experiencing with the car. I told him how quiet and smooth the engine was when you first started the car in the morning, however after a minute or two the glow plug cycle ended. and the engine started nailing.

He asked me if i had worked on the head of the engine, and I told him that the previous owner had. then he went on telling me about a bulletin that mercedes had put out. something to do with cold cylinders, after some one head work on the head, and cold cylinders causing the noise. he suggested that I power every glow plug individually to determine which cylinder was causing the noise, and after determining witch cylinder was bad he could lower the pop pressure of that particular injector, allowing more fuel, and by allowing more fuel, one would raise the temperature of that cylinder, I disconnected the connector for the glow plugs, jumped each glow plug directly to the battery and didn't had a significant change on the nailing sound?

Are all the cylinders colder than what they should be, or the nailing sound has nothing to do with this?

Why does it run quiet in the morning when is cold and like @#%^ after the glow plug cycle?

Does anyone know of any bulletin about head work on this engine?

And if temperature is the problem, can it be solve with a warmer thermostat?
Thanks.
1999 E300 151000 miles.