The present paper considers the processes of incomplete combustion in in-cylinder crevices with clearances slightly greater than quenching distance. For this, an experimental work has been carried out by using a premixed constant-volume combustion chamber. In the chamber, the propagation of flame through the combustible gas contained in individual crevices with various geometries was investigated by two means: high speed schlieren photography to obtain the idiosyncrasy of the in-crevice flame behavior; and fast-response thin-film thermocouples mounted flush with the crevice wall to measure the flame propagation speed, the instantaneous surface temperature, the instantaneous heat flux through the crevice wall, etc. From the investigation, the origins of unburned hydrocarbons formed in the in-cylinder crevices were surmised. In addition, an improved numerical method is presented for the computation of heat flux through a slab (here, the crevice wall) by using the timed surface temperature measured by the thin-film thermocouple.