I want to paint my air cleaner cover and horn cover black. They are both chrome at the moment. When I was cleaning, I found rust on the inside of both. I was going to wire brush and sand the inside then paint it just the inside black. But now I want to paint the whole thing black. Will I have to prep the outside to rough it up so the black paint will stick?

 

Yep. Use a red scotchbrite.

 

And use a metal etching primer so the paint bites into the metal. Any autoparts store should have some.

 

Yup, wire brushed mine, sanded, primed and sprayed with silver, welcome to Florida.
Oh ya did it again 18 months later, Ha!

 

Yes, you will definitely need to give it some bite. Chrome is hard to hold paint. If you want to make it look nice and last, take it to a powder coater. They can likely do it for next to nothing, and will last. Plus, you can often arrange a day to drop it off and pick it up the same day.

 

I always hit anything I paint lightly with a sandblaster, paint sticks like crazy after you do that.
I know not everyone has access to a blasting cabinet though.....but if you can use one, it works great.

 

No sandblaster access.

I'll have to check on getting it powder coated. Don't even know where to start looking in this area. How much do those usually cost?