Engine case metal aluminum or Silica Magnesium alminum alloy? Weld / Paint Q&A

[DuciD03]

Im curious Is Inner & outer engine case metal pure aluminum or a silica magnesium aluminum alloy?

or different for inner / outer etc? mostly curious about brazing migging or tigging cracked cases so alloy composition is important; along with much cleaning of surface and oil soaked metal.  Anyone had experience or is an aluminum welder? recall seeing some welded outer cases at one point.

Cheers D

[ducpainter]

Very little aluminum is in a pure form...it's too soft to be usable in that state. It's all an alloy. I have no idea what Ducati uses for it's cases and side covers.

[Dirty Duc]

They are cast, and weldable, so probably 319 or 356.
http://www.lbfoundry.com/319-aluminum-sand-casting.html

[ducpainter]

They are cast, and weldable, so probably 319 or 356.
http://www.lbfoundry.com/319-aluminum-sand-casting.html

...but the corrosion resistance isn't great. They could be 242 as it has good strength when hot.

[DuciD03]

... hum not an easy thing to answer; does it make a difference for painting? what primer / paint is used on aluminum alloy cases & heads? With the heat on the heads all AL alloy & paint must be special?

[ducpainter]

Aluminum needs either a chemical treatment, or an epoxy primer, and a paint with a high enough temp rating to withstand the heat.

I've used catalyzed urethane and it's held up. You need to heat cycle it to fully cure it.

[DuciD03]

Aluminum needs either a chemical treatment, or an epoxy primer, and a paint with a high enough temp rating to withstand the heat.

I've used catalyzed urethane and it's held up. You need to heat cycle it to fully cure it.

catalyzed urethane wow that must be pricy ... come to think of it ... you recommended I used a catalyzed urethane clear to protect a tank & wheel rims I wanted to last / look nice. touchy to use; I got some sags runs that I later carefully lightly sanded out before it fully cured; difficult to coat a tank & rims with all the angles ... but super nice finish / quality stuff.

chemical treatment; is that acid etch (primer) to eat through the al oxide; similar to fluxing that is supposed to remove the oxide layer? do you know what Ducati uses to paint engines?

[Howie]

Whatever they use I wouldn't.

[ducpainter]

catalyzed urethane wow that must be pricy ... come to think of it ... you recommended I used a catalyzed urethane clear to protect a tank & wheel rims I wanted to last / look nice. touchy to use; I got some sags runs that I later carefully lightly sanded out before it fully cured; difficult to coat a tank & rims with all the angles ... but super nice finish / quality stuff.

chemical treatment; is that acid etch (primer) to eat through the al oxide; similar to fluxing that is supposed to remove the oxide layer? do you know what Ducati uses to paint engines?

It also has a max temperature of over 300 degrees. I've used it before, and after heat cycling has been durable. It will be gummy the first couple of times it gets hot. Engines don't actually get that hot on the exterior.

Chemical treatment is typically done with a product called Alodine. It's a conversion coating that turns the oxide into a substance that prevents further oxidation or reaction with the chemicals in the paint.

Ducati uses the cheapest engine enamel they can buy in 55 gallon drums.

[DuciD03]

It also has a max temperature of over 300 degrees. I've used it before, and after heat cycling has been durable. It will be gummy the first couple of times it gets hot. Engines don't actually get that hot on the exterior.

Chemical treatment is typically done with a product called Alodine. It's a conversion coating that turns the oxide into a substance that prevents further oxidation or reaction with the chemicals in the paint.

Ducati uses the cheapest engine enamel they can buy in 55 gallon drums.

Thanks for that wealth of info... (modified the title to reflect what's being discussed).

What I'm gearing up to do is fill some holes in side cases I have as spares. Can't use them with holes in them;(so might as well experiment ...) Have also seen some info about welding alum alloy cases gets quite technical, especially if its a structural component; but If your a welder it looks doable; but even experienced welders are challenged to do good welds with cases, with inconsistent results due to the various factors that come into play.

So If using Alumiweld (zink-aluminum low temp Al solder) to fill some holes; does this have to be sealed in (oil bath) & out with a primer the sealing paint so it won't corrode over the long term? The case paint looks like a fine metallic grey with some satin clear? maybe a grey epoxy primer as Ducpainter ID'ed earlier (- must be difficult to work with if your not experienced -). 

A side note; I was cleaning oil off cases last night and noticed kerosene cleaned well; and If U used acetone it made the paint finish soft; so was reacting with the paint.

[ducpainter]

Epoxy primer needs to be topcoated if exposed to light. I wouldn't worry about the inside, but epoxy primer is very solvent resistant if you want to use it.