I've been using sprayed-on Dawn dishwashing soap on my greasy engine bits, as well as on any clothing or rags that have gotten grubby in the process of cleaning up motorcycles and other vehicles. No toxic fumes, and it really cuts through most petroleum-based yuck without roaching fabrics or metals. Not good for paint work (it'll take off most waxes), but fine for bare metals, particularly when used with a bit of soft brushing. I figure that if the wildlife rescue folks use Dawn for washing off wildlife caught in crude oil spills, it's OK for this purpose.