2Pcs weelye 12V550-40000RPM drive engine consists of a high-strength plastic plate and a high-quality motor. Please note whether the plum on the gearbox matches your child's electric car.Quick-change wire connectors that require no soldering to install and allow fast install/removal of gearcases!Please pay attention to the motor model. Voltage: DC 12V; Speed: 40000RPM ;Shaft Hole Diameter: 12mm (0.47); Length: 185mm(7.28) Max Width: 92mm(3.62); Motor Diameter: 35mm(1.38) Please check if your car is working properly.(Is the battery in a healthy state, outputting sufficient voltage; is the fuse blown, and is the receiver circuit damaged?) More speed gearboxes are available, please refer to the details page below. The RS550 model is not compatible with the RS390 model gearbox, as the gearbox size is larger and the installation aperture may also be different.