What paint for cast alloy parts???

[Fazed]

Need some suggestions folks.
Apart from powder coating, what types of paints have you used successfully on cast alloy items... things like brake calipers, engine casings, etc... must be rattle-can based paint.
I have a few items I need to paint (brake calipers being one of them) and I don't want to go down the powdercoating route. I was thinking Etch Primer followed by Enamel???
Trouble is with brake calipers... they contain brake fluid, which royally bu99ers most types of paint

 

[rikrobson]

Halfrauds do a brake calliper paint.

in Black or red i believe.

meant to cope with the extra heat. Brake fluid is meant to stay on the inside on the calliper and not the outside where the paint is so the shouldn't come into contact that often, unless you bleed your brakes the quick way

 

[rtbcomp]

In my experience a good etch primer is fine on ally. If possible have them grit blasted to give a rough surface for the paint to stick to.

 

[Unclefista]

For brake calipers, proper caliper paint is the best (suprisingly).
The 2-pack stuff really "sinks in" and brake fluid doesn't affect it..

 

[piman]

Hello Fazed,

Unless you use silicone brake fluid, that doesn't affect paint at all.

Alec

 

[Fazed]

Thanks people.
Piman... I sometimes astound myself with how dumb I can actually be. Never thought of silicone fluid (DOT 5?). Doh!

 

[piman]

Hello Fazed,

it's not that popular to be honest, and expensive relative to the conventional fluids. However, I believe it's properties are worth the cost and I've used nothing else for a very long time.

Alec

 

[langy]

I paint my calipers with Epoxy primer and 2 pack, been doing it for years now and never had any come off yet. Epoxy is the best thing for bare ally or GRP, Etch is a bit old fashioned these days.

 

[langy]

I personally wouldn't use silicone brake fluid, look up the various stuff on the web.

Thanks people.
Piman... I sometimes astound myself with how dumb I can actually be. Never thought of silicone fluid (DOT 5?). Doh!

 

[piman]

Hello Langy,

I've heard various arguments or supposed drawbacks with it. I have used it for thirty years on a large variety of cars and would use nothing else. Partly because my cars sometimes lie dormant for a while and the non hygroscopic properties of silicone mean it's less likely that there will be brake corrosion.

Alec

 

[langy]

Your call mate, all i will say is Lockheed thereselves are against the use of it, It features on the first inside page on the Lockheed application manual.

I build high performance cars for a living so i'm not prepared to take the chance i'm afraid.

Silicone brake fluid has a higher boiling point (around 700 degrees F.) than the ethylene glycol base fluids, but the major disadvantages is not Hygroscopic.
What this means is since it is not a glycol based, when moisture enters the system it is not absorbed by the fluid. This results in beads of moisture moving through the brake line, collecting in the calipers.
Its not uncommon to have temperatures in excess of 212 degrees F. (the boiling point of water), this collection of moisture will boil causing steam and vapor lock, this in turn will cause system failure. Silicone is also highly compressible due to aeration and foaming under normal braking conditions.

If you are changing from a glycol base fluid to silicone or the other way around. The two types do not mix so your system should be completely purged, disassembled and dried out. When the two fluids are mixed you will get a jelly like substance and it will really mess up your system.

Hope this makes sense.

Hello Langy,

I've heard various arguments or supposed drawbacks with it. I have used it for thirty years on a large variety of cars and would use nothing else. Partly because my cars sometimes lie dormant for a while and the non hygroscopic properties of silicone mean it's less likely that there will be brake corrosion.

Alec

 

[piman]

Hello Langy,

as I said, I'm aware of these reasons for not using silicone. The boiling point of water is as you say 212 degrees F, but that is at atmospheric pressure, what is the boiling point at pressures brake systems operate at, far higher? Why should moisture enter the system anyway, as you agree the fluid is not hygroscopic.
My cars are road cars not competition cars where the maintenance is far more stringent. How many people change brake fluid as they should? I have also heard that you don't get a firm brake pedal, that is not my experience.

Alec

 

[Fazed]

Now, now, kids... let's play nicely

The brake caliper in my o.p. is a small single pot sliding pin affair off a 125cc commuter bike, so I'm not looking for superbike levels of brake performance.

Piman; I couldn't find any silicone fluid locally so went to Halfrauds and picked up a small bottle of Dot 4 'Racing' brake fluid. Now, quite what the 'racing' bit means (apart from adding a couple of quid to the price) is beyond me, as there are no specs listed on the packaging.

Langy; I glass bead blasted the caliper at work (it's handy working nights in a place that has a floor-standing blasting cabinet which is only used with glass bead ) after masking off all the machined surfaces with Blu-Tac (the beads just bounce off Blu-Tac and it's far easier than nobbing around with tape). I then gave it a couple of light coats of Upol Acid Etch primer (good stuff... I use it lots), followed by a few coats of Gloss Black Enamel courtesy of a Halfturds rattle-can. I went with Enamel as I reckon it should be harder wearing than the normal acrylic stuff, which seems to fall off when it rains, let alone when brake fluid gets onto it.
24 hours gassing-off in the airing cupboard and we're getting there.
Whilst rebuilding the caliper with fresh piston / seals / pads etc., I got a few dribbles of 'Racing' brake fluid on the paint but it's remained intact so far.

This is what I started off with:

And now:

Thanks for all your suggestions guys, much appreciated

 

[langy]

The caliper came out nice enough, I mentioned the Epoxy primer as it's so much better than the old fashioned acid etch, it's adhesion is far superior and its also anti corrosive, it's used on aircraft & oil rigs of all things.