At first: I like the drive of the 103 train from KK Eishindo. It is not a good drive but it is useable to make a very good drive with it. To make this to a good drive, you need a worm, two gears type A with 20 teeth (or 16 teeth, if you have points on your layout) and a gear type B with 26 teeth (or 30 teeth in layouts with points), look drawing:
Without points on your layout you get a reduction 20:1, with points on your layout you get a reduction 16:1, that is more than twice as much as the original drive has!
At first replace the wheel gears with ten teeth through the gears type A with 20 or 16 teeth.
Then drill a 0.6mm hole in the gear box of the 103 train (picture 1).
Then cut the gear box (see red lines in picture 1 and 2).
The holder for the gear type B is now finished (picture 3).
Then glue the holder with the gear on the chassis (picture 4).
Now you just have to put the motor on it and connect it electrically. The result is a drive that drives much slower and quieter than the original one.
As a result of this modification, almost every locomotive with two bogies can be made to drive by shortening the chassis (look picture 5).
Good succeed!