Air compressor with improved rotating device

In an air compressor including a main frame provided with a cylinder and a motor, the cylinder being fitted with a piston body, the motor capable of driving a rotating device to have the piston body conduct reciprocating motion in the cylinder, the rotating device including a gear body that is assembled with a counterweight provided with a central axle corresponding to the center of the gear body and a crankpin placed at a distance from the central axle, so that the gear body and the counterweight rotates about the central axle, wherein the improvement comprises:

• the counterweight is horizontally divided into two integrally formed halves, including a left half and a right half, with a common line connected between the center of the central axle and the center of the crankpin, the left half having a weight different from the right half, whereby the piston body will gather more rotational momentum from the counterweight at BDC to facilitate upstrokes, so that the piston body can conduct reciprocating motion more smoothly.