Most 2-stroke gasoline engines use a set petrol-oil mixture for lubrication.
There are different kinds of oils and petrol-oil mixtures. They must be used according to the manufacturer’s specifications.
For small 2-stroke engines, the oil and fuel are pre-mixed.
A mixture of air, oil and fuel passes through a sealed crankcase on its way to the combustion chamber. That makes the crankcase part of the fuel intake system so it can’t be used as a sump.
As the air, fuel and oil enter the crankcase, the fuel evaporates, leaving behind enough oil to keep parts coated and lubricated.
The crankshaft and connecting rod bearings in 2-stroke engines are ball and roller types. Because the parts of this kind of bearing only roll over each other they only need a minimum of lubrication.
