i mainly use cox engines ,but after thay have been run they get covered in goo, from the fuel .
i thought maybe drop the whole engine in white spirit or something , but thought it best to ask here first ..
thanks chaps ..

Wipe it off with a paper towel and leave it alone. The oil protects it.

maybe clean it with a can of carb cleaner for everyday cars .. then give every part of the engine a shot of after run oil

I,ve found the best thing to use is domestic spray on oven cleaner.
I put my engine in a plastic bowl (or the kitchen sink if the wife isn't home), spray it liberally with oven cleaner and then let it sit there for about 1 hour.
Afer that, i just lightly scrub it with an old toothbrush and then rinse it with cold water. It then looks like a brand new engine.
I have even used this method on the inside of the engine to de-gunk the ball bearings. It works perfectly every time.

I have an old electric crock pot that I keep just for this purpose. ( Don't use it for cooking food after using it for cooking engines ) I take any O rings or other parts I feel may be damaged by this process. Cover the engine or parts with permanent anti freeze and turn on low over night. An old tooth brush is useful for brushing. ( don't brush teeth with this tooth brush either ) Permanent anti freeze is poisonous for humans and other living animals, birds, fish, worms or what ever.
Just as a side note; I read somewhere that in parts of Mexico the fliers use ( I guess the antifreeze is not as available) POTATO JUICE. I laughed at that when I read it, but decided to try it. IT WORKS. Took about a day and a half. Good cleaning -- Bob Bauer
PS -- NOTE: I think oven cleaner is too caustic and harsh to use for cleaning engines, however this is my opinion and others may argue the point. I WON"T

hi there. i'm a modeller from Scotland but registered as a member on your fine site. here's one way to really clean an engine on the outside only(never tried it on the inside). if you have a friend whose into photography,get some developing fluid from him, or buy it yourself apply it to the engine with a brush and watch that residue come off. don't leave it on too long though and wear gloves. the old fingers will go like walnut shells(wrinkled) if exposed too long to this chemical. remember to block any ports to stop fluid going into the engine i.e. , carburettor intake and exhaust port.
regards to you all
Lancasterjoe