an improved spring wound prime mover capable of use with toys is provided . a plastic resin housing member comprises a pair of housing shells having complementary locking pawls and keeper members to permit a snap together assembly . the housing member further supports a spring member that can be selectively connected to a gear train assembly having a first and second gear ratio . the first gear ratio includes gears with a higher degree of mechanical strength than those engaged in the second gear ratio whereby a durable gear transmission is provided that can run smooth for driving the vehicle .