In this article, we’ll look at how to get the best performance from a Lima ringfield motor. Some people at this point will say, “Convert to a CD motor “. We’re not covering that in this article so read on only if you’re interested in the original type of motor.
The ringfield motor is a fairly basic mechanism but it is robust and with a little work, will outlast many of today’s offerings. The usual criticism of the motor is that it’s noisy or sluggish but that’s usually down to the gear train and not the motor itself. The big advantage that this motor has is that it can be maintained and serviced very easily, unlike most modern sealed motors which, when they fail, need to be thrown away.
In this example, I am working on a motor from a Lima diesel class 31 but the principles are the same even if there are slight variations across the range. To keep things simple, the first thing that I am going to do is to de-solder the wires from the motor terminals. This isn’t necessary for regular servicing but for an initial tune up and to make the photography easier, it’s the best way.
With the wires out of the way, the next thing is to remove the motor bogie from the chassis. This is easily done by undoing the two screws holding the bogie frame to the motor frame. With the motor bogie released, we now need to look at the gear train. There is variation from model to model but the main difference is in how the gears are retained. There will either be a spring metal clip or two hexagonal bolts holding the gears in place. Remove the clip or nuts and then the gears, leaving them to one side. On the opposite side of the motor casing is the commutator cover, brushes and springs. Before dismantling, some words of warning : NEVER PICK THE SPRINGS UP BY HAND! No matter how careful you are, you will inevitably compress them, then they will ‘ping’ from between your fingers, never to be seen again! Use a cocktail stick when moving the springs, it’s the safest way!
Undo the two screws which secure the commutator cover and carefully lift the cover off. The two brushes and springs will either remain on the commutator or be stuck in the brass tubes. Wherever they are, move them to a safe place.
The commutator can now be lifted out from the motor casing, the ringfield magnet might come out too, depending on the model. Now we can begin to clean and service the motor.
The commutator will either be copper clad or have a silvered finish but in either case, it’s probably going to be black from the carbon brushes. The first thing to do is to clean the commutator; I use contact cleaner but meths, white spirit or isopropyl alcohol will do the same job. Using a multimeter, I check the resistance values between each commutator segment and its neighbours. They should all be around the 0.7 ohm mark. The next thing to do is to polish the commutator with a liquid abrasive like T-Cut or Brasso applied with a cotton bud or with Duraglit wadding. Finish the commutator off by removing any traces of liquid abrasive with contact cleaner, meths or white spirit.