any ideas how to stop corosion on cases under paint

restored my 390 last year blasted all cases and cleaned off with solvent de greaser,and repainted using pj1 case paint,pulled her out of storage and side cases are starting to blister under paint any ideas how to stop this ? i thought tha sand blasting would of got rid of any corrosion but obviously not blasted them off again and can see small areas like worm marks but give them a good blast was wondering if i could use something to stop this before paint ?or is it the solvent degreaser that has caused some kind of reaction before i painted any info guys would be appreciated as i dont want to do them again cheers.

I Posted this link I found easily with the help of the most popular search website in another thread here recently.
http://www.ehow.com/how_5863187_remove-corrosion-magnesium-aircraft-parts.html

Of course you could contact the paint source you used and see what they say as they seem to claim to be paint for exactly what you used it on.

I think I had asked about what to do inside the cases where the crank goes but no one seemed to respond. It would seem chromic acid is part of the solution by the source above.

fran

thanks frank bit gutted really as i really whent to town blasting and painting the cases and this has happened,not sure how to resolve problem to stop it happeneing again,acid etch primer would that help

yes it definately is the surface underneath ,when blasted i can see small corrosion/worm like marks i blasted last time soaked with contact cleaner and repainted straight away could it be the contact cleaner? but the crank cases are perfect? would a acid etch primer do the trick first or cut out the de greasing method and just paint straight away with pj1 thanks husky t any more input would be appreciated

You can prep as desribed in the article. I haven't done this with my 430 centercases because I couldn't get a good answer on neutalizing the corrosion. I think after prep, filling cavities with 2 part expoxy may be a better choice than JB weld

going to try a acid etch primer after sand blast and not going to use any kind of de greaser and see what happens,then pj1 case paint

yep will keep you informed

I had done some research on this, as I am having the same dilemma. I found a product called "Magnadyne" made by PolyFiber that is used throughout the aircraft industry to treat magnesium surfaces. It is a chromic acid bath that you dip the parts in and then let them dry, similar to the Dow17 or Dow 7 process. Magnadyne has recently been discontinued and I cannot find a similar product. You can make up a solution if you are a chemist, but I am not. I initially soda blasted my engine cases to remove the original paint and corrosion. I am now delayed without this conversion coating product. I have confirmed that the magnesium cases did indeed originally have a conversion coating (Chromic Acid surface treatment) by observing a gold iridescence on the base metal once the paint was removed by blasting. I would not repaint without reapplying this conversion coating, especially if corrosion is present. If anybody can find a similar product to Magnadyne that is readily available then please post as we all have magnesium cases to deal with. I am also unsure of what kind of paint to use on the inside of the cases that will be resistant enough to oils and the 2-stroke crankcase environment. It seems that the original paint was some sort of epoxy? I have heard that Glyptal will work, but this stuff is red in color and would be nice to find something black.