dhermesc........... for many, many years, the manufacturers of air cooled engines SPECIFIED non-detergent oils to protect their product. These engines were all splash-lubed and therefore oil filtration was not possible. Instead, they told the owner/users to change they oil every 10 or 20 hours of use so that the bulk of the contaminants would flushed out of the engine and clean oil would prevail. However, that procedure did not stop varnishes, soot and other contaminants from sticking to the engine block and other components, often building up a coating that would continue to grow in size.
When some well-meaning but highly mis-informed individual comes along and decides to switch over to a detergent based oil, that coating begins to dissolve and quickly contaminate the clean detergent oil with engine killing particulate. That is WHY owners continue to use NON-detergent oils in 2018. Even consecutive oil changes will not remove all of that contamination. The only answer is to tear the engine down and boil all of the parts ( block, oil pan, crankshaft, camshaft, gears etc) to make them perfectly clean. ONLY at that point can one safely use a detergent base oil. Even then, the frequency of the oil changes should be shortened because the detergent oil will keep the particulate in suspension until the drain plug is removed. YOU vastly underestimate how long it would take detergent oil to scrupulously clean an old air cooled, splash-lubed engine. There are many types of oils out there......FOR A REASON. There is place for detergent based oils and there is also a place for NON-detergent based oils.......even in 2018.