I've rebuilt several engines over the years and always used spray bombs to paint them. The paint always fades, chips and peels off in places despite what I thought was proper prep. Cleaning oil leaks meant the paint would sometimes get dull from the harsh cleaners. This time I figured that paint sprayed through a gun with hardener/catalyst would shine more and hold up better.
Ironically, the engine doesn't LEAK! There are no spills to clean so far.
