300D injector lower body black coating
 

Removed my injectors to replace nozzles, and soaked them overnight with
degreaser.
The next morning about 75% of the black coating came off.
Maybe it's a powder coating or tool/gun Blueing type of finish.
Thinking to re do them with a gun bluing kit.
Any DYI suggestions?

Gun blue would be most sturdy and better than what the factory used if something different. I have seen injector bodies look different. One group of 3 in my 1984 car were a uniform dark black w/ lettering vs the more pure metal, perhaps blued, of my originals. I recall they said rebuilt, so might have been a coating from a Bosch factory. They also stated the pop pressure for a non-turbo (proved true), so wondered why someone put them in my turbo engine.

[QUOTE=BillGrissom;3704996]Gun blue would be most sturdy and better than what the factory used if something different. I have seen injector bodies look different. One group of 3 in my 1984 car were a uniform dark black w/ lettering vs the more pure metal, perhaps blued, of my originals. I recall they said rebuilt, so might have been a coating from a Bosch factory. They also stated the pop pressure for a non-turbo (proved true), so wondered why someone put them in my turbo engine.


The ones in my 300CD seem blued and these ones in the 300D seem powder coated.
You're right I think Gun Bluing would be the way to go.
Have to find a small DIY kit, maybe a gun store.
Thank you

They can be blued with cold gun blue or hot blued.

The originals were blued like a gun but I believe later they used a black phosphate finish. It is more costly the a simple bottle of gun blue but they sell tool blacking kits or you can look on the internet for a do-it-yourself version (the main chemical is phosphoric acid).
Keeping them to long in the acid eats up the parts somewhat as you saw by leaving the parts in the degreaser.

I just saw a youtube video about welding where they showed how a "black oxide" coating is applied to bare steel. Looks fairly simple. You buy a powder (phosphate?) in a bag and dissolve in hot water. You first degrease the part well in another hot water solution, dip in the oxide solution ~3 min, brushing the surfaces helps, wash in water, and dry. They said the oxide is a chemical conversion which doesn't change dimensions but adds microscopic pores. You then coat w/ oil and it gets absorbed to protect from rust. Seems that is what they do on "impact sockets" and similar tools. From what I know of physics, the black comes from the microscopic pores acting as "black-body cavities". Physicists would use stacked razor blade ends similarly to absorb laser beams.

thanks everyone.
Good info!
Jeff

I picked up a small kit of "Birchwood Casey Permablue" for gun blueing,
followed the instructions.
The lower injectors are nice and black now!

Very peaceful and relaxing to just lay under the car, and do nothing for a while.
Hot day, cold driveway, cold beer.
Anyone with me on that?

Wow!
What a difference!
Installed the Injectors with new Monark nozzles back into the 300D.
0 smoke and increased power!