Originally Posted by
spock
I wouldn't recommend WD40 unless you wanna squirt it in there all the time, because as soon as it disappears, rusting comes back stronger. WD40 is an extremely strong solvent.
Actually I wouldn't worry about it at all as long as you keep riding your bike, because regular vibrations usually shake the rust off on the inside because it isn't exposed external elements as much.
I`m sure you heard that stuff about WD40 somewhere but unfortunately none of it is true. There are more urban myths floating around the Internet about WD40 than any other consumer product I`m aware of.
The WD40 website has a complete FAQ plus a lengthy list of recommended uses. It might be worth a visit. Its original claim to fame (and the reason for its development in the first place) was based on its effectiveness as a rust inhibiter when sprayed on the outer skin of military missles. Its not a strong solvent and any properties it has as a degreaser are based on it consisting largely of light mineral oil - which basically dilutes heavier oils and greases with a little elbow grease.
However - that light mineral oil will displace water and permanently adhere to metal - since all metals are porous by nature. If you doubt that then an interesting challenge for you might be to try to paint any metal object that been treated with WD40. As per your post since its a strong solvent - the metal should have been perfectly prepared for painting. Good luck!