 Only in the 1960s did Japanese motorcycles introduce the now- familiar horizontally-split clam-shell which has become almost universal.Modern horizontally-split four stroke engines invariably use single oil reservoir (whether wet- or dry-sump; but while this simplifies matters, it is arguable that the previous system of having different types of oil for engine and gearbox is preferable.The BMC Mini was an early example of a car with the "gearbox-in-the-sump"; but this practice of using a single oil reservoir, which has become the norm for motorbikes, is generally undesirable for cars and trucks.