cover them with a plastic bag or clingfilm.
get some autoglym engine and machine cleaner. wash the engine when it's cold. the heat dries the cleaner out before it's done it's business. make sure you do it on the road as it'll leave oil and sh!t all over your drive otherwise.
might need to do it twice. work it into the stubborn areas with a old (or someone elses) toothbrush. you'll have a engine like gtijoes in no time
