Some Japanese brass used Pittman-style motors with wishbone springs for brush tensioners. One leg of the wishbone spring was insulated, and the other was bare. All you have to do to insulate the `grounded' brush is slide a bit of insulation stripped from a wire over the bare end of the spring.
Older brass locos with open-frame motors are, typically, juice hogs. They require high-capacity decoders. If in doubt, go for the highest-capacity decoder that will fit.
Chuck (Modeling Central Japan in September, 1964 - with 1960s brass)
You should poke around with an ohmmeter to make sure that you have isolated the motor. Some motors were wired by simply bending one tab over and soldering it to the motor frame to complete the circuit.
The ohmmeter should put to rest any concerns that the motor is not completely isolated. Remotoring is another option to be considered.
Isolating the brushes is all you have to do. If this an open frame motor it is best to determine amp draw before hooking up a decoder. Most of the older open frame motors will draw too much and the decoder will be working at its maximum and when stalled will exceed the max and possibly blow the motor drive circuit.
Pete
I pray every day I break even, Cause I can really use the money!
I started with nothing and still have most of it left!
Very easy to determine. Use the ohm meter function in your multimeter and see if there is any connection between the shaft and either motor lead. There should be no continuity. I have never seen a motor with the shaft connected to a motor brush.
Rich
If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.
In isolating the motor for decoder instalation, is islolating the brushes adaquate, or do I need to isolated the shaft from the metal bearing on the gear end. Isolating the frame is easy, but where the shaft goes into the brass bearing, it is all soldered to the frame. It seems to me that isolating the brushes from the frame would be enough and I could then just solder the decoder to the brushes.