Proper locomotive maintenance is essential if you want all of your models to last the long haul. A small investment of time and effort can pay off more than you expect.
Many railway track repair firms provide track maintenance services online. You can also search online for experienced railroad contractors. Some train models require lubrication after 100 hours of operation, others recommend it every 6 months.
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For any O-size locomotive, as soon as you see it behaving differently, always check the wheels first. The same is true for the g-scale. They work. HEAVY! Then check some connections and switches.
It's always a good idea to know a lot about your model car so you can fix it yourself. What if the wheels are clean but the locomotive starts and stops on its tracks? Brush wear is a possible cause, as brushes typically experience relatively more or less friction.
In this case, the best thing to do is to replace the brush. Watch for signs such as stopping and stuttering. If these things happen, you almost certainly have a problem with the brush.
Check out the right brush for your locomotive at your local model train shop. Again, you need to use the manual and follow the instructions carefully.