there are several ways but unless i am doing a rebuild after many years of use i do not bother with the out side of the engine except to just wipe it off and oil it after a days flying sesion.i also run the tank dry on the last flite and land deadstick to keep any fuel left in the engine from rusting bearings.have been doing this for over 30 years and while my engines are not new looking they are not blavk or brown either and they do not look like they have been used for 30 years constantly.