It's very important to get all the grease off any kind of part your going to paint. If not it will turn out bubbly with spots/holes.
Engine degrease, then use a power washer, even a garden hose with a high pressure nozzle will work. It's best to leave the degrease on there for a few minutes, then spray it off. Then apply another coat and scrub the areas that are caked on with grease.
Spray it good with water, let it dry then paint