Muratic acid will eat the aluminum and not hurt the cylinder. Put some on a qtip and put on the aliminum. Keep applying till its gone. then light hone.
Use muratic acid, it should bubble and smoke alittle. If it doesnt you need some fresh stuff. Then use a ball hone with some oil. Thats always worked for me. Watch out for the smoke it can be kinda intenese at times!
muratic acid and a little heat will help. I use a propane torch and warm the spot I'm working on, and it goes much quicker. Your local hardware store should have some and and dabble it on with a brush. Were rubber dishwashing gloves, AND DON'T GET ANY ON YOUR CLOTHES!