Straight motor oil of any weight not a good idea for a bike chain. It is to thick to penetrate the pins, rollers, and bushings, where most chain wear occurs. Much better is to use a mixture of 4 parts odorless mineral spirits, and one part synthetic motor oil. Apply a couple of drops to each roller, wipe the chain with a clean rag and you are done. It is a good idea to do this the day prior to a ride, as the mineral spirits will have evaporated, leaving behind the oil, and allowing the chain to stay cleaner. Never use WD-40, as its lube properties fairly suck for a bike chain.