We made a study on the combustion chamber deposit (CCD) formation pattern on a piston crown surface in a small two-stroke spark ignition engine. Generation of the CCD is influenced by the temperature, pressure, gas flow conditions or retention period of the lubrication oil in the cylinder. Temperature profiles on the crown were estimated with fusible plugs which have known melting points in advance. Lubrication oil flows were observed by generating CCD streaks from many small drilled holes on the piston crown.