Page "Two-stroke engine" Paragraph 35

Most small petrol two-stroke engines cannot be lubricated by oil contained in their crankcase and sump, since the crankcase is already being used to pump fuel-air mixture into the cylinder.

Traditionally, the moving parts ( both rotating crankshaft and sliding piston ) were lubricated by a premixed fuel-oil mixture ( at a ratio between 16: 1 and 100: 1 ).

As late as the 1960s, petrol stations would often have a separate pump to deliver such a premix fuel to motorcycles.

Even then, in many cases, the rider would carry a bottle of their own two-stroke oil.

Taking care to close the fuel-tap first, he or she would meter in a little oil ( using the cap of the bottle ) and then put in the petrol, this action mixing the two liquids.