Make it shiny!

Aluminium parts oxidise overtime and ruin your bike’s looks. But with time and basic tools they can be brought back better than new.

ASTEVE COOPER

luminium parts, like engine casings or fork legs are generally polished and lacquered, painted or even just polished. But over time, stone chips, salt and ultraviolet light break down the coating, allowing the finish to get very second-hand.

Gradually the finish delaminates more of the protective coating to a point where the casting grows a furry grey overcoat. Painted cases can be cleaned back, filled where necessary and then repainted; all in all a fairly straightforward job.

Polished case rectification takes a little more effort. It’s a messy job but we can do it at home. There are several DIY polishing solutions out on the market and it pays to have a look at what’s available. Our friends at Perfect Polishing have supplied a restoration kit for us to use.

BASIC PREPARATION

The kit should do pretty much all we need for an average bike and comes with the all important dust mask etc.

This is a messy and noisy job with bits of mop, alloy and buffing soap getting flung about, so a dust mask, strong gloves and safety specs are the absolute minimum needed to work safely; I also add in a disposable boiler suit and earplugs.

Make sure absolutely nothing like sleeves, cuffs, belt etc can get drawn into the polishing mop. To be able to polish effectively the alloy needs to be free of grit, grease, dirt and protective lacquer. The first three can be easily removed with a brush, some bike cleaner and hot water. The lacquer needs more aggressive techniques and paint stripper is normally very effective in removing this. It’s also possible to blast lacquers and paints off but bear in mind the surface may be slightly rough; it’s okay for paint primer but will take some extra buffing to get back to a smooth surface.

Here I’m using gelled aerosol type stripper which clings to vertical surfaces while it does its job. Another option is to use one of the more aggressive abrasive kits with either satine mops or abrasive polishes. However, remember that whilst these abrasive processes will remove overt damage, they are also marking undamaged alloy. Because we are dealing with abrasive there will be a need to

remove the fine scratches imparted on the alloy by the process.

With the alloy clear of dirt and coatings we can get a good look at the metal underneath and make a reasoned assumption as to how good or bad it is and what steps we need to take. If the alloy is just dull and unmarked it’s viable to start with the coarsest mop (a sisal one in this case) and some polishing soap of the corresponding grade. However, if the alloy is badly marked, scratched or pitted it may be necessary to bring in some strong arm tactics. Huge pockmarks or holes are better treated with one of the alloy welding kits advertised within CBG; with a bit of practice it should be possible to effect good repairs.

This Yamaha XS650 side case had suffered from damp storage and was quite seriously corroded but it has been brought back to a uniform condition with emery cloth, DIY flexible sanding blocks and decreasing grades of wet-and-dry paper. I’m also using a second cut file to carefully shave off any big dings while still preserving the original profile and then redressing as above.

By using progressively finer abrasives (whether by hand or on a mop) it should, with time, be possible to get a surface that will readily polish up to an acceptable level.

Finally, unless you have a workshop area you can dedicate to polishing it’s probably best to do it outside; it’s inevitably a messy process and you don’t want the debris all over your bikes or work area.

ON THE MOPS

Selecting the appropriate tail or pig for the direction of rotation of our drill or grinder, the sisal mop is screwed on. With the mop running we can add some of the buffing soap designed for that specific mop; a quick one or two second application is normally sufficient. Now we can finally bring the alloy (in this case a rare carb cover) into contact with the mop and by applying pressure the dull surface can be removed. More soap is added when the buffing tails off. It’s important to move the work piece around to prevent hollowing; also the angle of attack should be varied so that the alloy is not all polished in the same direction. If this happens you will see parallel tram lines along the surface that will show up on the finished item.

The sisal mop is used until the work piece is uniformly buffed and further polishing doesn’t enhance the sheen. Next we move onto the second, softer, stitched, mop which will remove the coarser mark of the sisal one. Again using the appropriate buffing soap we can repeat the process using similar techniques. The second cut mop is often the one that does a lot of the work but at a slower overall rate than the coarser sisal version. There’s sometimes a tendency to think the effects are tardy and add extra soap. If this happens it’s possible to end up with extremely tenacious, big black, smeared, scuds of soap and metal particles on the polished surface – the

excess soap can be removed by carefully running a clean wire brush over the rotating surface of the mop if necessary.

Don’t be tempted to use abrasives or an old brick to do this as any hard particulates picked up on the mop will then damage the article being polished. Wire brushes are generally unlikely to leave bristles in the mop face.

Finally, we’re onto the soft calico mop and removing the polishing marks left by the stitched mop. Time taken here to cover every facet of the substrate will be rewarded with a gleam that will satisfy most of us. Then we need to rub the surface over with some Vienna lime to remove any residual polishing soap, grease or finger marks and the job’s a good’un as they say.

All that’s left to do is possibly give the readily oxidisable surface a coating of protective wax polish and it’s time to move onto the next job. Sharp-eyed readers will note I’ve not polished out the marks in the top face of the carb cover. As the intended bike has a patina of wear I’ve elected not to go over the top but rather carry out a sympathetic refurbishment.

If there’s a fair amount of polishing to do it makes sense to do it outside and have sufficient mops and buffing soap on hand. Always allow more time than you think the job will take if you’re new to this and aim to finish a certain number of parts with the final calico mop rather than do all the roughing out in one hit. Firstly you can then do something else next time rather than get terminally bored with a bike’s worth of polishing; secondly you get to see some genuine results for one day’s work rather than moving from dull grey to slightly brighter grey.