Cleaning aluminium pores

[koolio]

I started with a rough set of cylinders which were blasted clean then wiped down with lots of acetone.

They were unpolished with a keyed surface, next day I coated them with VHT gloss black enamel paint. After letting them rest for a week and oven cooking them, I can literally scratch the paint of with my little finger it's not holding whatsoever.

I'm told the vht paint shouldn't be this weak and that this is due to the oil impregnating the pores of the aluminium which I failed to remove despite all of what I did above.

Wanted to ask what do you guys do to really clean an aluminium engine for example for welding or painting etc. where oil contamination will become most apparent don't want to make this mistake again.

 

[AlphaDogChoppers]

Bake at 400F for a couple hours.

 

[o1marc]

Or longer if they are still smoking after 2hrs.

 

[koolio]

But how does the baking get rid of the oil? Or does it just cause it to leave the pores? Surely cooling will make it return back into the pores?

Should you wipe it down immediately after with acetone?

 

[trek97]

After letting them rest for a week

I dont think I remember reading that step on the can?!?!

Did you primer them?

Baking them is a great idea. I will do that before they go in the Kenmore. next time.

Get em spotless w acetone. then I toss em in dishwasher w cascade. HOT HOT HOT. Then more acetone.

If you do the jugs. Be ready w a towel. as soon as the dishwasher stops yank em out and start rubbing. the cylinders will flash rust instantly.

this last time I did use Metal etcher on a couple of the small covers...next time I will use it on the entire engine.

did you properly cure them according the instructions on the can?

 

[trek97]

I could be wrong. Its been a year now, but I think I got all the priming, painting black, curing, painting red, clear coat and curing again done in one day. you need wait 10 minutes between coats and get em on within an hour. If it goes over an hour you have to wait 7 days between coats.

the reason for this. Is, upwards and after 1 hour, a coat has acquired a "dry skin" on the surface. It is still wet underneath. At this time, Adding a fresh coat over the top, The thinner in the fresh top coat will attack the dry skin, kinda like stripper. causing it to separate from the wet underside, And wrinkle it up. If you recoat within 10 minutes to 1 hour the skin on the previous coat is still fresh (wet, soft) enough to accept the top coat without this happening. kinda like melting (bonding) the two coats together as 1. After 10 minutes the first coat has time enough to become tacky and is less prone to running as you add the second.

The paint is very fragile before its cured. If you do something weird like I did (layering different colors and textures). cure between coats and Let the parts cool down before you add more coats. then your ready to spray and cure again. If you try to tape off flames on the uncured paint...the tape will pull the paint off.

 

[AlphaDogChoppers]

But how does the baking get rid of the oil? Or does it just cause it to leave the pores? Surely cooling will make it return back into the pores?

Should you wipe it down immediately after with acetone?

The oil burns off, hence the smoke that Marc alluded to. The oil will ooze out of the pores, make smoke, and leave carbon residues on the surface which you may have to soda blast off.

 

[o1marc]

As Alpha Dog knows we run into oil problems in powder coating all the time. Some things that are bathed in oil in it's normal life are very hard to get all the oil clean before proceeding with the coating. If powder coating them we would run them through that "outgassing" or in this case a "burn off" cycle at 50-75* above cure temp (450-475*) for an hour or more to be sure all the oil has burned off and then media blast them to remove all residue. At the higher temps the pores will open and release the oil to flow out and burn itself dry so it doesn't flow back into the pores when cooled.

 

[AlphaDogChoppers]

I had a Norton inner primary case recently that was the worst I had ever encountered. Very porous casting. I had to bake it all afternoon. Filled my PC room with smoke. Then I sandblasted it again, and got good results. Had to use aircraft stripper and sandblasting to remove my first failed attempts at powdercoating it.

The owner of the bike wanted me to do the outer primary too. I wanted to polish it because I thought it would look better. He took it to another powdercoater, and was very disappointed with what he got back.

 

[pacomotorstuff]

Last night, I degreased with lacquer thinner and then used Alumiprep 33 prep agent on some rocker covers and machined aluminum fittings (BTW, I prefer lacquer thinner over acetone because it's evaporation rate is slower and with a blend of solvents. a greater chance of dissolving more contaminants).
The Alumiprep instructions specifically say not for (aluminum) castings but sometimes the old shit we work on needs "extreme measures" and they were permanent mould castings, not sand cast anyway and not going on an aircraft fer sure.
Laid on some paint which cures really slowly, so will probably nail it with some heat tomorrow. I'll let you know how the paint adhesion is afterwards.
I've been using Alumiprep 33 for many years, a standard aerospace aluminum rejuvenation agent - contains phosphoric acid among other things. Pretty straightforward if you follow the safety and application instructions.
To really enhance paint adhesion on aluminum, alodine can also be applied afterwards (its a chromated conversion coating) but it might be a little over the top for us guys.
As far as the entrained oils, first a good solvent scrub, then industrial-strength soap and lots of scrubbing as preliminary steps...?
Hope this helps.
Pat

 

[AlphaDogChoppers]

I prefer lacquer thinner over acetone because it's evaporation rate is slower and with a blend of solvents. a greater chance of dissolving more contaminants).

Yes, that blend of solvents include toluene, xylene, and MEK. All highly toxic.
Those are all chemicals that I don't care to be exposed to. Acetone is much safer from a health perspective.

 

[trek97]

So, see nothing to it...simply follow these 521 simple steps and 4 years from now your engine will be ready for the first coat of primer!

 

[koolio]

Thanks guys, alpha and all of you.

I guess what was missing in my cleaned cylinders was the heating part, I had them blasted then acetone and they were spotless, next time I'll cook them up before like you guys said.

Sounds like this isn't a bad idea to do in general even if you are just going to be polishing the alu rather than painting it?

The VHT I used didn't need a primer, plenty of people recommending not using it with primer and having good results without. I did the painting by the book, so within 20 minutes or whatever not longer than an hour, instructions mentioned I didn't need to cure in an oven I did it when I realised paint just wasn't sticking.

I only use phosphoric acid on aluminium that is in very bad/rough condition usually for getting rid of corrosion etc. I make sure to dunk it in a large bucket of water when done.