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Newbie, trying to find best way to finish aluminum-LONG POST

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  • Newbie, trying to find best way to finish aluminum-LONG POST

    I did a writeup of a project I have currently undertaken to fix up a motorcycle swingarm made of aluminum. I would like it to finish as closely to the factory finish as possible. So here is my writeup, it's long so be forewarned. I'm pretty much a complete novice at this so any help, explanations, and patience with my ignorance is greatly appreciated.

    Swingarm Work

    Let’s start off with some early pics of the swingarm in the condition it was in.

    We’re just looking on the RH side to start since this is the only side I’ve worked on thus far. Notice the scratches and small scrapes in the middle, far right and between the two circular factory marks. Closeups to follow.

    Above is the damage in the middle of the swingarm.

    Far right

    A little left of the scratches on previous pic

    This pic is the LH side that shows another pic of the factory finish:

    First I should mention that I tried using some of the Aluminum paste from Solder-it that can bond aluminum pieces together or fill in holes and such on aluminum pieces. You are supposed to heat the paste to a point where you see bubbling of the material. This is the flux point which is supposed to infuse the paste with the right chemicals to ready it. Once you see the bubbling, the instructions tell you to apply more heat and the paste will form the aluminum-like solder finish. You can guess that this is more difficult than what the instructions tell you about, so I practiced on a sheet of aluminum foil and tried to find the best way to work with it. If you torched it too fast or hot, you would get a yellow/brown redsidue. If not enough heat was applied, the paste did not form into a solder-like material and was more like a porous stone-like consistency. You could even torch it so hot that I saw was just a burnt black residue, not what you want on an expensive piece of a motorcycle.

    So I was finally ready to apply it to the swingarm. I’m working with pretty small amounts of this paste and on a flat or contoured surface mind you. Well I apply the paste onto the scratches/divots and start to heat. I can see that that the flux material seems to just be spreading out away from the paste as I heat it. There doesn’t seem to be as much smoke as there was when I was practicing and not nearly the effect of overheating. I’m getting the porous material finish. I try applying more heat with the torch but I can see that nothing is happening. I feel the material and it is brittle and there’s a waxy/oily residue, I’ll assume from the flux chemical that was spreading out. I’m able to cleanly wipe the material away and it looks like I haven’t done a thing, back to square one. I try again starting with more heat, but the flux spread can’t be avoided. I do get the aluminum solder-like material to form but this is clearly not melded with the swingarm aluminum, I can wipe it away as before. Screw this, I’m bagging the paste until I can figure out how this thing works. Perhaps a more patient individual might just stop here and re-organize and form a different plan of attack after consulting with others, forums, solder-it support, etc. But a patient man, I’m not. So I proceed…

    Well now that the paste is not working for me, I figured to just sand these blemishes and see how it goes. The pics that follow are from this point on.

    Spot sanding with 40 and 80 grit sandpaper by hand:

    After using the palm sander and going through a succession of finer grits of sandpaper with the sander (100, 180, 320, 400), you can see that it’s not finishing like I had hoped. The damage spots that were sanded and some surrounding areas are shinier and other parts that were avoided still have the factory finish but now all scratched up. I’m assuming this is due to the fact that the anodized layer is protecting the aluminum underneath. Whereas the damaged spots that I hand-sanded had most of the anodized layer taken off so those spots are bare aluminum. See 2 pics below:

    At this point I know I should start back with the courser paper and redo the whole side (F@#!). I figure by sanding down the whole side, at least or hopefully it’ll look the same throughout and then I can figure out how to finish from there. I started with 40 and 80 as before:

    Then worked thorough 100, 180, 320, 400, 600, 800, wet sanded with 1500, then 2000 grits. The pic below is before the finer grits, I think it was after 320 or 400:

    This pic was taken after the final 2000 grit was used. The dark and light haze was from after the wet sanding, the wet sanding powder residue kind of caused it to look this way. The 2000 grit was used dry and this pic was taken after wiping the swingarm off with a damp paper towel. It was getting late, I was hungry and thirsty so I left it like this ‘til next time. I’ll see what else I can do but as it stands now, the scratches are all smoothed out but still have some fine sandpaper swirls.

    I would like to get it looking like what you see in the earlier pics, don't really want the chromed finish which is a bit too shiny for what I want here.

  • #2
    Been there. My motorcycles don't have alum. swingarms, but other parts that started looking pretty rough. What I thought was going to be a sand, buff, and polish right quick turned into a OH, S&*%$, it's got a coating. Then quite a few hours doing the whole part by hand. You look like your about well into it. From first hand experience, I recommend Caswell's alum. polish kit. It comes with everything but a fast drill and a couple of old t-shirts to do what you want. It beats the fire out of hand rubbing. I did a part today that I had sanded to 400 grit, then with the kit, made it look like chrome in 1/3 the time or less than by hand. There is a sticky post on polishing bikes that is very informative. Lotsa luck.


    • #3
      Thanks for the input.

      I ordered the black and brown compounds along with a spiral sewn wheel last week and just waiting for it to come. Will post an update


      • #4
        Project update

        Well, I applied the black and brown compounds with spiral sewn wheels. I started on one small section with the black compound but saw that it was not smoothing out all the imperfections. In fact, some scratches were now even more noticeable as other areas were polishing and becoming shiny. I tried to continue with the black hoping that the scratches would eventually come out, it did not.

        I figured that my original sanding was to blame so I went back to sanding from the start with 120 grit then working up. I hoped that this would get out the deeper scratches that were still visible after polishing.

        After sanding down, I started with black then followed by brown on the spiral sewn. The pictures tell the story, but I still have these visible imperfections

        Would the black compound on a sisal wheel be what I should use to get these out? Then move to the brown with a spiral sewn to obtain a better finish.


        • #5
          What grit did you finish with on the sanding and are you doing it by hand or sander? Looks like some jitterbug swirls. Did you work across the deeper scratches? Sometimes it takes a little bit to get the hang of things.


          • #6
            I finished with 1500. Original sanding was with a sander but with this last time was by hand. Maybe a faster drill and/or larger wheel is what is in order? I was using a 1/2 hp hand drill w/ 3 in. wheel for the polishing.


            • #7
              If you still have some deep scratches, go back to the palm sander with some 150 or 180 grit to get them out. You will really have to look hard because sanding will hide the scratches a bit. After you think you have them out, go to 320 or 400 grit. You should be able to tell how well you did two grit changes prior. Sounds confusing a little. What I mean is you should not have to back up more than 1 or 2 grits if you missed something. The more you do, the better you'll get at knowing what to look for and the finish you need before changing to the next grit.