A crank device and an adjusting device of a combustion engine. The system adjusts the cylinder pressure of the motor in accordance with the required power. Adjustment of the cylinder pressure takes place by changing the compression ration by means of the adjusting device (19). The adjusting device (19) changes an eccentric wheel (3) through an adjusting wheel (4) to a such position that a connecting rod (2) lifts a piston (1) to a desired distance from the combustion chamber head. The adjusting device measures the volume of the air entering the cylinder and adjust the compression ratio to be appropriate. The adjusting device also takes into account the speed of rotation so that the compression pressure increases or decreases to be appropriate.