depends on how delicate the surface is and how caked the dirt/carbon is.
Detergent strength (soft for delicate, bearing, light dirt surfaces/seals -> strong for heavily caked non-bearing metal surfaces)
wd40
washing powder
petrol
brake/carb cleaner
Agitator (soft for delicate, bearing, light dirt surfaces/seals -> aggressive for heavily caked non-bearing metal surfaces)
cloth, shirt, rag
brush in washing powder
scotch pad
wirebrush (manual or wheel)
rust remover wheel