Some engines are more beautiful than others, take the Vincent Black Shadow as an example; it’s prettier than Salma Hyack in the niff eating strawberries. Back in the day the aesthetic of the engine was an integral part of a motorcycles beauty, there was no need to chrome pipes or paint engine casings other than to make them look pretty, unless you buy a top of the range sportscar, for example, the engine that grumbles under the bonnet is there purely for the sake of it’s function. The thought of tarting it up to catch the eye contains about as much logic as plopping in the bathtub.
It’s safe to say that whilst jolly nice to gawp at a motorcycle engine isn’t known for it’s aero- dynamism so covering it up with a smooth panel in order to increase speed efficiency and cut down on drag of both machine and rider was wholly inevitable.