A rapid compression-expression machine can simulate intake, compression, expansion and exhaust strokes in single internal combustion engine cycle. The accuracy of the piston position at the end of compression stroke is determined by letting the actuator piston impact against the end plate of the actuator case. At that time, a dwell period presents about 7ms. For removing the period, the design and manufacturing of a size reduced device is tried. A pneumatic cylinder is used as down scaling model of a rapid compression-expression machine. An elimination of the dwell period is tried by incorporating a motion converter in this. At first, chipped teeth gear mechanism is adopted. This mechanism could produce a reciprocating stroke during one stroke of the pneumatic cylinder, but the piston behavior at top dead center was disturbed. Next, we adopted crank mechanism and developed a motion converter newly. As a result, the motion converter using the crank mechanism was confirmed that it was effective for elimination at a piston dwell period of a rapid compression-expansion machine.

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