Painting aluminium components

[Tim L]

On my last build I painted the barrels black. I put a lot of time into the preparation and the engine looked pretty good but after a few weeks lots of small lumps appeared under the paint. Does anyone have any tips on painting the barrels to prevent this happening.
I am also painting wheel rims and hubs, fork legs and the crank cases so any tips and hints would be gratefully accepted.

 

[Scrambled]

Better off getting your aluminium parts polished , paint on aluminium always fails after awhile and polished aluminium looks much better .

 

[Tim L]

I wanted shiny black wheel rims and hubs with stainless steel spokes.
I also wanted the barrels and top end to look better than they do as they have been left in the rain for quite a few years by the PO.

 

[jd750ace]

All aluminum is best chemically etched in prep for paint. Although self etching primers are out there, the etching is not inspectable. In the aircraft business it's always a seperate process. When it comes to cast or forged parts, a vapor degreasing cycle is highly recommended for prep to ensure there are no trapped pockets of chemicals or moisture. Blisters in painted cast goods that are subjected to heat are nearly always caused by micro boiling of chemical or water moisture.

 

[ridgerunner1965]

you mite try powder coating.

old alum bike parts can be really hard to degrease totally because alum has pores the oil can sink really deep in causing probs later.

 

[jd750ace]

Vapor degreasing is done by heating to evaporate any fluids from the pores. It's generally repeated several times if preparatory work is a wet process.