Originally Posted by
bhtooefr
...You'll also notice that engine camshafts are universally driven by either a belt, chain, or geartrain, all of which preserve direction of rotation.
Not totally universal. Ducati motorcycles used to use shafts running up the side of each cylinder to turn the (desmo) cams, and there were others.... Of course motor vehicles have a lot of excess horsepower, so a bit of loss in gearing and power transmission isn't as consequential as it is on bicycles.