My builder (Pete @ Hybrid Engineering) strongly suggests that you do not powder coat cases. The heat can soften the aluminum and your main bearing bores will get loose. The cases were heat treated after casting by Honda. When you heat them over a certain temperature for a extended period it will anneal the aluminum. That can cause a big time failure. But! I have seen a ton of atv and motorcycle engine cases running around that were powder coated. I just choose paint.
Loren
The above is very true!
I cannot count the number of times customers have had the structural integrity of aluminum parts ruined because they had them powered coated. Any time an aluminum part is raised over 300 deg. F the temper of aluminum starts to change.....the higher the temperature above 300 deg F...the faster the temper clocks ticks. Most of the powders coats require over 350 deg F to cure.
I do not recommend Powder Coating any aluminum parts, unless your are building a museum Queen and do not care about the strength, and thermal aspects of your engine parts.
I want my customers engines to get rid of as much of the waste heat as possible without having to depend entirely on the radiator. The cooling system actually consists of all of the external surfaces of the engine cases, cylinder, head, radiator, and hoses.
Paint is a thermal barrier or better know as an insulator. Powder coat paint is a better insulator than conventional paint because it is much thicker. Polishing a surface will have a similar effect as painting a surface. Polishing/painting a surface reduces the amount of heat that can be radiated off hot engines surfaces. The emmisive power of a sandblasted aluminum surface is almost 5 times higher than that of a polished aluminum surface. The emmisive power of a powder coated surface is much less than that of a polished surface. The emmisive power is a number that engineers use to compare the amount of heat that can be radiated from the surface of different materials with different surface textures.
In summary:
The following list will show the type of surface or surface treatment that will radiate the most heat. Number 1 will radiate the most heat and 6 the least amount of heat.
1. Sandblasted or heavily oxidized
2. Machined surface
3. Polished surface
4. Painted
5. Polished Chrome plated surface
6. Powdered coated
Numbers 3 and 4 could trade places depending upon the type of paint and thickness
Do everything you can to help reduce the amount of heat your radiator has to dissipate. Your cylinder and head probably have at least 50 times more surface area than those finned aluminum gadgets that many guys insert into their radiator hose in an attempt to make their engines run cooler.
Polishing and paint makes things look a lot nicer and easier to keep clean. The big question is: Do you want to keep your engine components as cool as possible or build a Museum Queen?
