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A study of the characteristics of combustion knock in a 1 cyl prechamber diesel engine is reported here. The intensity of the knock showed pronounced cyclic dispersion and an electronic counting technique was developed to measure the intensity distribution. The knock had a major frequency of 2370 Hz and was most apparent at low speeds. Advancing fuel injection timing and also increasing rate of fuel injection increased intensity. Tests with a wide range of fuels showed that cetane number was the only fuel property important to knock. A study of the relationship between knock intensity and the pattern of combustion pressure development showed that the time origin of knock was at or near the position of maximum rate of pressure rise, and that knock intensity could be related to a time function of pressure rise.