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