Engine casing corrosion

[komatias]

Hi All,

I am in the process of repainting some engine housings. It seems that the passivating of the aluminium was not done properly while in the BMW factory or wateva. So... I have the casings acid bathed to remove the old paint and all was fine.
They are ready for powder coating but I noticed yesterday that I got some white fluffy salts accumulating on the surfaces where it was more corroded initially. Is there anything I can do that will help prevent this before the powder coating goes on?
Chromateing phosfating or anodising is not easy at the mo because I have already masked the bits.

Any thoughts?

Cheers

George

 

[Shep]

Sand or bead blasting should clean them sufficiently well without causing the masking to lift if you are careful.

Shep

 

[komatias]

so you think that just removing the surface corrosion is enough?

 

[Shep]

Normally raw alluminium needs stablising before coating, ally chrome was a term we used to use alot but i'm not sure of the official name for the process.
This was done before any paint finish was applied.

Shep

 

[komatias]

Yup thats passivating using chromate salts... should have been done at the factory but by the looks of my casings it was not done properly...... bugger... I'll ask the powder coater...

 

[King Rat]

It seems this was a problem with many of the 1150 bikes - my yolks, fork bottoms, cylinders, heads and the manifolds are all peeling their coating - despite not having been left dirty. WD40d from dry and kept coated - I just use half a can on the bike after a wet ride and washing. There were plenty redone under warrenty too - so nothing knew.

Be interested in what your powder man says because mine are going to have to be done at some stage.

Ta.

 

[Stickleback]

so - the 1150 is not without problems then! Rather got the impression that the 1150 was superior in ever respect to the 1200

 

[ianboydsnr]

so - the 1150 is not without problems then! Rather got the impression that the 1150 was superior in ever respect to the 1200

Its a beemer, its all about levels of faults

 

[komatias]

Actually its a F650gs engine but I have seen the same happen to many a 1150+ bikes. I guess they skimped on the passivation of the aloys after a few runs...

 

[falcoron]

prep

Hi All,

I am in the process of repainting some engine housings. It seems that the passivating of the aluminium was not done properly while in the BMW factory or wateva. So... I have the casings acid bathed to remove the old paint and all was fine.
They are ready for powder coating but I noticed yesterday that I got some white fluffy salts accumulating on the surfaces where it was more corroded initially. Is there anything I can do that will help prevent this before the powder coating goes on?
Chromateing phosfating or anodising is not easy at the mo because I have already masked the bits.

Any thoughts?

Cheers

George

If the powder coater is any good he will have a prepaint prepping process, which will probably include a phosphate wash of some sort. He should not coat any sustrate that is unsound. I got my Corroded rear adv rack blasted and pretreated then powder coated with a polyester primer coating for aluminium. this was then painted with standard 2 pack acrylic car paint by myself. The Polyester primer coating is less porous and adheres better to alloys(according to the powder painter) All i can say is this was a great job.
Im a wet paint sprayer so no expert on powder coating but the principle is the same you cant paint over shite and get a good results.
Hope this helps
Ron