I would like to know which is the process of painting used on the primary box of a harley davidson. (The flat black)

 

I think it's krinkle black powder coating.

 

I've always heard it's wrinkle/crinkle black powdercoat.

 

As other have said... powder it....

If you are dead set on DIY....
Scotchbrite it... Primer it.... then Paint it....
I would go with a heat resistant paint to be on the safe side...

CC

 

Its wrinkle black powdercoat. But harley makes this paint in a can called textured black I used it when I scraped the bottom of my primary and its not as wrinkled but its close. So you can try that maybe.

 

Are there any companies that specializing in powder-coating Harley powertrain parts? I have a 2008 Nightster that I'd like to convert into a Sportster Custom.

 

Eastwood makes a powder coat kit that does an excellent job. The first one I bought was less that a 100$ and I just upgraded to a dual voltage one for 150. The first one works just as well. I went to the garbage bailer and found an oven for free and use my compressor plug when I need to use the oven as their both 220. It's so easy to use and they carry a powder call HD paint that's semigloss but comes out with some texture. They also have the wrinkle black and about anything or color you want. Just did a pair of junk twin cam rocker covers with the wrinkle black as a test and you have to look close to see where the chrome was peeling. They turned out so awesome I put them on my 2011 Fatboy. Now if I could ever figure out how to post pictures to these posts I'd share the results. I did my cam cover, tranny end cover, and the primary cover with the HD Black. Like the look better than the silver color Pearl came with.