The undercarriage system of the excavator is a complicated construction, composed of tracks, rollers, and gears, which can be regarded as the “leg” and the “foot” of the machine. It is bearing the whole weight of the machine body, providing the traction on the most rugged terrains, and at the same time ensuring the stability that is demanded for the lifting of the heavy objects. Because this system is occupying a great portion inside the life-long maintenance cost of the machine, therefore, for any owner or operator who is wishing to extend to the maximum degree the normal running time of the machine and to protect his investment, it is being of extreme importance to understand its components and to carry out the proper maintenance.