Choosing Paints

I'm fond of powder-coating, but it holds in heat, and it melts in the 350° to 400° (Fahrenheit) range. So it is only useful for the outermost engine parts (if at all) and for body and running gear parts. Wait -- I just found out that some new powder-coat formulations can bear the heat of air-cooled cylinders and heads. Now it's a matter of determining how efficient they are at conducting the heat away from the engine into the atmosphere. I am cautiously excited. One problem: I like to prep parts before machine work and I am told by the chrome/ceramic/Nikasil bore people that cylinders must be dipped in a bath that strips EVERYTHING down to the parent aluminum. Ah well.

After some experimentation, I decided to go with high-temp Rustoleum -- they have a truly gorgeous silver, suitable for the new look on cylinders and heads -- and VHT paints. They have a nice black metallic with a light gold cast to it: good for high compression cylinders. Both heat-cure with a hand torch in about three minutes.

Somewhat Later

So I decided to prep some cylinders and heads for the next round of performance parts. I shot the heads with VHT high-temp black, and the barrels with Rustoleum engine enamel. I shot a light coat, waited ten minutes, shot another light coat, then waited half an hour and shot a somewhat heavier coat. Then I waited. I kept everything in the sun as much as possible (>= 10hrs a day). A week of this went by. I then took everything and played a MAPP gas torch over each for about ten minutes -- until all smoking stopped. I waited another day. Then I applied a file to the fin edges. On the barrels (Rustoleum) the paint came off as a powder; the way aluminum responds to filing. Excellent. I turned to the heads. The paint came off in chunks and strips, leading into areas where it was needed, but no longer adhered, Extensive touch up will be necessary. I'm going to cheat -- I'll spray some Rustoleum onto some disposable surface until it puddles, then apply it to the heads with a q-tip. Once I'm happy with all finishes, I'll shoot Rustoleum clear, let it sit for a week, then "heat treat" it.

I'll let braveness overpower discretion and work the parts then -- have the cylinders bored; port match and give multi-angle valve jobs to the heads. Then a final touch up if necessary.

If you have a high quality epoxy paint, you have an excellent heat barrier. It is also very durable as what the "epoxy" in the name refers to is the matrix holding a high percentage of ceramic. If you decide to refinish or change color, stripping off the ceramic is difficult: it's hard. It's also unnecessary. Heat flows essentially unimpeded but slowly across the layers - there is no barrier effect.

Topics

So just degrease and hit the surface enough to rough it up for better adhesion and spray on the new coat. Transitioning layers is not a problem. It is a problem if you use paints of different types. To my knowledge, this only works when both are epoxy, and to play it safe maybe use the same brand with the same temperatures listed on the cans. This also works when both paints are enamal-based. As for stacking an enamal on top of an epoxy - or vice-versa don't do it; there are border effects.

NOTE WELL: Make sure that somewhere on the can it says oil and gas resistant. Otherwise, something is left out of the matrix and the paint (even if it's been cured) will run. I prepped some heads with my top-of-the-line cams. Shortened the guides; matched up the ports; 7 angle valve job; and shimmed the rockers; tedius work. I generated some aluminum dust and rinsed it off with gas. The paint ran off as if it has just been sprayed. I was pissed and offered the customer a price break if I didn't have to start over. He said to strip the heads and we were more-or-less both happy.

A final note: when I use Rustoleum spray paints (even with their "easy spray" cans), I always get some paint on my trigger finger no matter how careful I am. It's an annoyance that only takes a few seconds of scrubbing with a Scotchbrite pad to fix, but it indicates a flaw in the delivery system. And it's one that they appear unwilling to address.

I'm still looking for a paint that conducts heat away better than bare aluminum. Any input (backed up with some technical details) would be greatly appreciated.