Crankcase

Two-stroke engines typically use a crankcase-compression design, resulting in the fuel/air mixture passing through the crankcase before entering the cylinder(s).

The fuel/air mixture does not pass through the crankcase, though a small amount of exhaust gasses often enter as "blow-by" from the combustion chamber, particularly in engines with worn rings.

Then as the piston travels downward, the inlet port is uncovered and the compressed fuel/air mixture is pushed from the crankcase into the combustion chamber.

[2] Crankcase-compression designs are often used in small petrol (gasoline) engines for motorcycles, generator sets and garden equipment.

Unlike other types of engines, there is no supply of oil to the crankcase, because it handles the fuel/air mixture.

[5] Oil from the sump may splash onto the crankshaft due to g-forces or bumpy roads, which is referred to as windage.

The spaces between the crosshead piston and the crankshaft, may be largely open for maintenance access.