DrIsotope

It really wouldn't. Motor oil is designed to be operated under pressure in a sealed environment. Oil is kept inside an engine mechanically. Take an exposed chain drive to 5,000rpm, and the centrifugal motion and generated heat would have the chain almost completely clean within minutes. This is precisely why exposed chain drives in industrial applications use grease. Motor oil will work in the short term for as I said before, virtually anything will work in the short term. I don't eschew motor oil as a chain lubricant because I'm some kind of lubricant snob. I don't use it because it's absolutely the wrong material for the application.