For my '87 300SDL, nailing was cured by replacing the cracked #14 head with a new #22 head. The IP, prechambers and injectors were kept with the new head so my conclusion the new head or at least the new head gasket resolved the nailing.

owain, I'm guessing you mean you have a '90 300D. It's not likely an OM602 has a cracked head but a failed head gasket, by way of oil leaking into the #1 cylinder, is unfortunately common.

Wagnerwerks, I'm guessing from another post that you have a 78-85 300SD. It's not likely an OM617 has a cracked head or a failed head gasket.

For both of you, I suggest isolating the nailing by loosening the injector lines one at a time. The nailing injector should quiet when it loses fuel pressure. Swap the nailing injector with another injector in the engine to see if the noise follows the injector or stays with the cylinder. That information will give the forum plenty to chew on.

Some folks, maybe only a few, have cleared nailing by running a bottle or two of LiquiMoly/LubroMoly Diesel Purge. There's a process to this - it's not effective if you dump it into the fuel tank or let the return line continue directly to the fuel tank while purging.

Sixto
87 300D^2