The flowfield in a motored axisymmetric reciprocating internal combustion engine is calculated as a function of space and time throughout the complete four stroke cycle, by means of a computational procedure which solves the governing partial differential equations on a mesh which expands and contracts with the motion of the piston, using an implicit, iterative, finite-difference scheme. Numerical results are presented for laminar and turbulent conditions. In the last case, two additional conservation equations, the kinetic energy of turbulence and its dissipation rate, are solved. In both cases, an axisymmetric configuration and a centrally-located valve, which opens and closes instantaneously have been studied. The results corresponding to the laminar case show the formation of a large vortex during the intake stroke. As the fluid is compressed, the intensity of the vortex decays, and its decay persists throughout most of the expansion stroke. The turbulent case results show that the turbulence is clearly generated during the intake stroke due to the shear layers on the sides of the incoming air jet and is then convected and diffused through the cylinder.