Three dimensional air motion in a motored diesel engine has been studied using hot wire anemometer. Three probe orientation technique was adopted to obtain the three components of the velocity at the point of measurement. The probes were calibrated in a high pressure and high temperature wind tunnel. The variables studied are engine speed, valve masking (size and orientation) and compression ratio. While solid body type of motion is observed during the early stages of compression, compound vortex type of flow is found to prevail during the later stages.