Guess I should have clarified which problem with the headset this will fix. It won't fix the corrosion problem. Also, if your top headset bearing is worn out and loose this won't fix it.
However, if your headtube is popping because the top bearing and bearing retainer are moving around and the bearing retainer is slipping past the bearing ridges this will be a permanent fix... not a preferred fix, but definitely a permanent fix.
The ACR design came from FSA and Vision Bicycle Components. They might be the same company, not sure. The motivation for the hidden cables, I'm guessing, comes from the need to reduce wind resistance in triathlon bikes. Somehow, someone thought it would look clean on a mountain bike so they used the design there. In my opinion the ACR design doesn't work with mountain bikes because the headset bearings and head tube have to withstand much more force from the fork steerer tube and the ACR design doesn't allow for that. In my case, my front wheel slid directly into a tree and all of my weight and momentum put a huge amount of force on the top headset bearing and I heard a distinct pop. I thought maybe I cracked the frame. After that I started getting regular popping in the headset. When I inspected the headset I could see why it was popping.
The bearings and the head tube and the bearing retainer in the ACR design are kind of like the concave and convex washers of a brake bolt. They are able to slide within each other and only the angle of contact between the surfaces keeps them centered. If the retaining force applied is not straight down the steerer tube the parts will not be able to maintain correct positioning. Since the ACR top bearing retainer only makes contact with about 60% of the bearing surface it is not able to apply consistent force all the way around the bearing and so it tends to slide toward the lack of support. And since the lack of bearing retainer surface is at the front of the head tube where the most force is applied, there is not enough of a metal ridge to keep the bearing and the bearing retainer in place. When the bearing retainer is turned 90 degrees the bearing is held down with more force in the front and there is a metal ridge there to keep the bearing retainer in place. So now there is no movement between the pieces and no popping. The weakness in the bearing retainer is moved so that side forces can disrupt the positioning but the side forces applied to the head tube are insignificant compared to the force from front and rear - no risk there.
I'm including pics of the top bearing retainer. You can see where it had been slipping past the bearing and causing the popping.
There are other solutions from FSA and Ritchie but the FSA solution is not available and the Ritchie solution is cost prohibitive when $50 shipping from the UK is added.
I bought the FSA ACR replacement bearing and it sits lower in the head tube so won't move as much but decided that it was not necessary once I figured out the source of the problem. You can buy the bearing alone from Amazon for $22. It came without the black zinc oxide coating which is partially why I wanted it. I have another solution for the rust issue though.
https://www.amazon.com/dp/B00RW5FQB4?psc=1&ref=ppx_yo2ov_dt_b_product_details
