So the easy way (FYI hard way thinking you can do this by hand)
Step 1: Clean the swing arm thoroughly, no dirt, oil or grease should be left on it, i used scotch brute pads and soapy water, use brake clean or acetone as the final clean. CLEAN WITH BRAKE CLEAN OR SOLVENT AFTER EVERY STEP.
Step 2: Remove rough finish, and pitting / porosity - Use a 5" angle grinder with a flap disc 120 grit or even 150 grit if you can find it. If you can only get an 80 grit, wear it out a bit on a piece of steel first. Smooth out as much of the swing arm with this step, CAREFULLY - DO NOT PUT "OOPS" LINES OR CUT MARKS FROM THE EDGE OF THE DISC"
Step 3: There are some hard to reach areas, use a dremel or die grinder with a small flap wheel to smooth these areas out, again the finer grit you can find the better.
Step 4: Now remove the grinding lines from the flap disc. For this use a drill, a cordless drill will NOT work, they don't have the power or the rpm to do this properly so don't waste your time. You will need a sanding disc mandrel (5") for your drill, get the velcro style one, preferably with a layer of foam in it so it can contour to the surface slightly. Use 240 grit sanding discs (wet or dry) to start, you can use water if you like to cut down on dust (I didn't, but wear a dust mask, ALUMINUM DUST IS EXTREMELY BAD FOR YOU). save the worn out 240 discs for later use. The worn out ones remove the lines from the fresh ones, this can save you from buying 20 different grits of discs.
Step 5: Use your dremel with a sanding disc mandrel to get into the hard to reach areas, cut your own discs from the 5" ones you bought. I went with 1 1/4" diameter, use a thin felt polishing disc as a backer for the sanding disc so you can get some pressure on the work piece. Remove the previous grinding lines in the hard to reach areas.
Step 6: Repeat steps 4 & 5 with finer grit discs (I went in this order - Fresh 240 grit, worn 240 grit, 1200 grit, 1500 grit, worn 1500 grit. Polish until you can only see 1500 grit sanding lines, and use the 1500 grit discs until they wear out, they will bring close to a mirror finish on the area you are working.
Step 7: You will need a 4" or 5" cloth buffing wheel and mandrel for drill, and a small cloth buffing wheel for the dremel. You will also need some "Tripoli" polishing compound (I used ENKAY brand). To put compound on the buffing wheel just "polish" the bar of compound a bit, you don't need much on the buffing wheel for this to work properly. You will see on the wheel it basically just stains the cloth a bit, you can figure out if you have enough or not pretty quickly by just trying it out. DON'T USE TOO MUCH OR IT WILL NOT WORK RIGHT AND JUST SMEAR POLISHING COMPOUND ON THE SURFACE. To polish the surface you don't need to use much pressure at all, and you should see pretty much instant results, the sanding lines will go away and you will start to see a mirror finish.
Step 8: Clean the surface well with acetone or brake clean, use a SOFT rag for this.
Step 9: You will need another fresh buffing wheel for the drill, and the dremel (you can't use the previous ones with the finer compound). This time use "White Rouge" polishing compound (again I used ENKAY brand). Apply this EXACTLY the same as in Step 7. This step should really start to show a brilliant mirror finish that would make Harley guys jealous.
Step 10: Apply aluminum wheel polish. I recommend using "Xtreme Polish" ONLY. There is no other polish like it on the market, it is impregnated cotton and it works AMAZING. You apply it by hand, it goes on in a milky liquid. Rub it on there for a while until the surface turns blackish, no need to let it dry. Rub it off with a clean SOFT rag, at first its will look dark and cloudy. Wipe as much as you can off with first rag, whats left on the surface should be dark and dry-ish. Grab another clean SOFT rag, and rub it until you reveal the awesome shine underneath. You should now have a ridiculously bright polished surface, and you will see your face with a huge grin staring back at you in the mirror like finish.
Step 11: Xtreme polish does make a sealer to help protect your polished surface. This would be an optional step. Re-polishing with the wheel polish regularly with help keep the surface looking great.
Hope this helps you get through this project, steps are the same for side rails, or frame hips, or pretty much anything made from aluminum. Every once and awhile a but of hand sanding was needed to blend areas in. If you do these steps diligently, you could polish your swing arm in only a couple hours.
Clay \m/ \m/
Pictures today, if I have time.