Thank you for this awesome tip!
Now that it's been a few years, have you noticed any negative effects at all?

I really need to do something about my engine case, and I'd rather not paint it bc I'm afraid I'm just gonna mess it up.

 

I spray Simple Green on the under carriage, then soak the remaining bike with a light mixture of Dawn and water. Hose it off and leaf blow the water away best I could. Looks off the assembly line clean. I've never really soaked a bike down like I do my passenger vehicles until I had to run thru a lot of melting snow that left a big mess. I used to just wring a washcloth with Dawn soap and towel dry in the past. I was so impressed with how clean it looked after doing a 'soak' wash that I'm going to use that method from now on.

 

Ive since powder coated the engine covers. That said, I dealt with the grey wrinkle for a few years without issue after doing the scouring pad. Knocking the rough part off the finish was essential for me maintaining a clean Nightster. Keep in mind you dont want to rub the finish completely off. Just enough so that you can smoothly run a cloth across it without it gripping like sandpaper. Fwiw, my engine looked just as bad as yours in the beginning.

Tried all of those things (see post 1) no success with the grey wrinkle engine casings on the Nightster.

 

I use a cheap alloy wheel cleaner foam and a circular motion with a washing up brush on mine .