You said not impossible, and you tried different compounds and abrasives. But you didnt say what worked.

 

I used a bottle brush of the appropriate size on mine...gets inbetween the fins real well.

 

+1 on the baby bottle brush.

 

He is not talking about in between the cylinder fins, he is talking about the machined edges of the fins. The machined edges are not coated and the elements eat into the exposed aluminum, pitting it. You would need to remove aluminum past the the pitting.
I do not recommend sanding because the paper folds around and does not stay perpendicular to the surface, sanding the black coating and making it look worse. Part of the problem is that the fins are stepped as you move up so you have to pretty much do each on individually.
You need some thing sturdy and slightly flexible to scrape the oxidation off. If the oxidation is light you can take a razor blade an scrape it off, very tedious and be careful not to scratch the black. Just keep the blade perpendicular to the machined surface and scrape and try not to gouge or it will look like crap, one reason I like the flexible razor blade and don't recommend a gasket scraper. This worked for me on some of the surfaces but not all, some of the pitting or oxidation is too deep and I am resigned to the spottiness of it.

I am actually looking for some rough cast cylinders and heads to replace the machined ones, I think they look better anyways.

The S100 says on the label "avoid letting it dry on the surface", my once and only time I used S100 it made my black slightly chalky and I will never use it on the engine again and it did nothing for the oxidation on the machined fins.
Just my
CB

 

He said not possible!!! And nothing worked!

 

Steel wool! Works great!

 

I tried the foam backed nail files and different abrasives but just got a dull finish. I think re-machining is the only way to get them back to a bright finish, so nothing I tried got the finish back.
On a new bike you just have to keep after it and not let dirt sit on the fins. My brother just got a S100 kit with his new bike, I think there is a protectant they make that I would try to keep this from hapening.

 

I tried steel wool, did not work on mine.

Mike

 

Steel wool does work, IF you don't let it get too bad before trying to remove the oxidation. It's a very tedious process of doing one fin at a time, but the results are like a brand new cylinder fin.

Once the oxidation (or any pitting) get really bad though, your probably going to need to try something else.
Perhaps a Dremel tool, with an abrasive disc? But you'd have to be very careful and not get into the black portion of the fins.

 

Anyone has more opinion on the oxidation fin???

I'll try steel wool tonight to see if it work!
People told is better wash the engine with soap and water sometime, I see my friends bike older then mine, but doesn't have this problem!